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Macronutrients
The treatment of anaemia depends on the cause. Notably, however, about 50, to 40, years ago, human beings appeared to have taken a Great Leap Forward, when human culture apparently changed at a much greater speed. Carotenes are present in good quantities in a wide variety of green and yellow vegetables and fruits, in yellow maize and in yellow root crops, e. The mucosa is rich in mucus-secreting glands, which together with saliva ensure adequate lubrication for the purposes of speech and mastication. Others—citing the tendency of technologically advanced human societies to enslave or wipe out less advanced societies—argue that it may be dangerous to actively call attention to Earth. In many populations, particularly in the industrialized countries of the North and among affluent groups almost everywhere, diets do not depend mainly on locally grown foods.

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Human nutrition

It is often difficult to know what to do when the child is cured, especially if the child is under one year of age. There may be no mother or she may be ill, or she may have insufficient or no breastmilk. Instruction and nutrition education are vital for the person who will be responsible for the child. If the child has been brought by the father, then some female relative should spend a few days in the hospital before the child is discharged.

She should be instructed in feeding with a spoon or cup and told not to feed the child from a bottle unless he or she is under three months of age. The best procedure is usually to provide a thin gruel made from the local staple food plus two teaspoonfuls of DSM or some other protein-rich supplement and two teaspoonfuls of oil per kilogram of body weight per day. Instruction regarding other items in the diet must be given if the child is over six months old.

The mother or guardian should be advised to attend the hospital or clinic at weekly intervals if the family lives near enough within about 10 km or at monthly intervals if the distance is greater. Supplies of a suitable supplement to last for slightly longer than the interval between visits should be given at each visit.

The child can be put on other foods, as mentioned in the discussion of infant feeding in Chapter 6. It is essential that the diet provide adequate energy and protein. Usually kcal and 3 g of protein per kilogram of body weight per day are sufficient for long-term treatment. Thus a kg child should receive about kcal and 30 g of protein daily. It should be noted that a marasmic child during the early part of recovery may be capable of consuming and utilizing to kcal and 4 to 5 g of protein per kilogram of body weight per day.

There is little doubt that a disorder due mainly to energy deficiency does occur in adults; it is more common in communities suffering from chronic protein deficiency. The patient is markedly underweight for his or her height unless grossly oedematous , the muscles are wasted, and subcutaneous fat is reduced. Mental changes are common: It is difficult to attract the patient's attention and equally hard to keep it.

Appetite is reduced, and the patient is very weak. Some degree of oedema is nearly always present, and this may mask the weight loss, wasting and lack of subcutaneous fat. Oedema is most common in the legs, and in male patients also in the scrotum, but any part of the body may be affected.

The face is often puffy. This condition has been termed "famine oedema" because it occurs where there is starvation resulting from famine or other causes. It was commonly reported in famines in Indonesia and Papua New Guinea.

Frequent, loose, offensive stools may be passed. The abdomen is often slightly distended, and on palpation the organs can be very easily felt through the thin abdominal wall. During palpation there is nearly always a gurgling noise from the abdomen, and peristaltic movements can often be detected with the fingertips. It is not uncommon for adult kwashiorkor patients to regard their physical state as a consequence of abdominal upset.

For this reason, strong purgatives, either proprietary or herbal, and peppery enemas are sometimes used by these patients before they reach hospital, which may greatly aggravate the condition. The hair frequently shows changes. The skin is often dry and scaly, and may have a crazy-pavement appearance, especially over the tibia.

Swelling of both parotid glands is frequent. On palpation the glands are found to be firm and rubbery. Anaemia is nearly always present and may be severe. The blood pressure is low. There is usually only a trace of albumin in the urine. Oedema may also be caused by severe anaemia. In adult PEM there is less dyspnoea than in anaemia and usually no cardiomegaly. Other features such as hair changes and parotid swelling are common in adult PEM but not in anaemia.

However, the two conditions are closely related. In contrast to adult kwashiorkor or famine oedema, which is not very prevalent, the adult equivalent of nutritional marasmus is very common. There are five major causes. Any older child or adult whose diet is grossly deficient in energy will develop signs almost exactly like those of nutritional marasmus, and if the condition progresses it may often be fatal.

In the case of famines, the condition may be termed starvation see Chapter Famines and severe food shortages resulting from war, civil disturbance or natural disasters such as droughts, floods and earthquakes may result in nutritional marasmus in children and a similar condition in adults, who suffer from weight loss, wasting, diarrhoea, infectious diseases, etc.

The second major cause of severe wasting or severe PEM in adults is infections, especially chronic, untreated or untreatable infections. The most common of these now is acquired immunodeficiency syndrome AIDS resulting from infection with the human immunodeficiency virus HIV. As the disease progresses there is marked weight loss and severe wasting.

Advanced tuberculosis and many other long-term chronic infections also lead to wasting and weight loss. A number of malabsorption conditions cause PEM in adults and children. These diseases, of which some are hereditary, result in the inability of the body to digest or absorb certain foods or nutrients. Examples are cystic fibrosis, coeliac disease and adult sprue.

Another cause of wasting in people of any age is malignancy or cancer of any organ once it progresses to a stage not treatable by surgical excision. Cachexia is a feature of many advanced cancers. A group of eating disorders cause weight loss leading to the equivalent of PEM.

The most widely described is anorexia nervosa, which occurs much more commonly in females than males, in adolescents or younger adults rather than older persons and in affluent rather than poor societies. Other psychological conditions may also result in poor food intake and lead to PEM. Treatment of adult PEM includes therapy related to the underlying cause of the condition and therapy related to feeding and rehabilitation, when the cause makes that feasible.

Thus infections such as tuberculosis or chronic amoebiasis require specific therapy which when effective will eliminate the cause of the weight loss and wasting. In contrast, curative treatment is not applicable in advanced AIDS or cancer.

Dietary treatment for adult PEM should be based on principles similar to those described for the treatment of severe PEM in children, including those recovering from kwashiorkor or marasmus. Emergency feeding and the rehabilitation of famine victims described in Chapter 24 have relevance to adult PEM. It is much more difficult than controlling, for example, iodine deficiency disorders IDD and vitamin A deficiency, because the underlying and basic causes, as described above, are often numerous and complex, and because there is no single, universal, cheap, sustainable strategy that can be applied everywhere to reduce the prevalence or severity of PEM.

Part V of this book includes various strategies to reduce the prevalence of PEM. Appropriate nutrition policies and programmes are suggested, and separate chapters deal with, for example, improving food security, protection and promotion of good health, and appropriate care practices to ensure good nutrition.

These chapters provide guidance on how to deal with the three underlying causes of malnutrition, namely inadequate food, health and care, which in Chapter 1 were included in the conceptual framework for malnutrition. Other chapters in Part V discuss solutions to particular aspects of the problem, including improving the quality and safety of foods, promoting appropriate diets and healthy lifestyles, procuring food in different ways and incorporating nutrition objectives into development policies and programmes.

Throughout Part V there is an emphasis on improving the quality of life of people, especially by reducing poverty, improving diets and promoting good health. Improving the energy intakes of those at risk of PEM is vital. In the late s and s it was thought that most PEM was caused mainly by inadequate intake of protein.

A great deal of emphasis was placed on protein-rich foods as a major solution to the huge problem of malnutrition in the world. This inappropriate strategy diverted attention from the first need, which is adequate food intake by children. There is now much less emphasis on high-protein weaning foods and on nutrition education efforts to ensure greater consumption of meat, fish and eggs, which are economically out of the reach of many families who have children with PEM.

Protein is an essential nutrient, but PEM is more often associated with deficient food intake than with deficient protein intake. In general, when commonly consumed cereal-based diets meet energy needs, they usually also meet protein needs, especially if the diet also provides modest amounts of legumes and vegetables. Primary attention needs to be given to increasing total food intake and reducing infection. Sensible efforts are needed to protect and promote breastfeeding and sound weaning; to increase the consumption by young children of cereals, legumes and other locally produced weaning foods; to prevent and control infection and parasitic disease; to increase meal frequency for children; and, where appropriate, to encourage higher consumption of oil, fat and other items that reduce bulk and increase the energy density of foods fed to children at risk.

These measures are likely to have more impact if accompanied by growth monitoring, immunization, oral rehydration therapy for diarrhoea, early treatment of common diseases, regular deworming and attention to the underlying causes of PEM such as poverty and inequity. Some of these measures can be implemented as part of primary health care. Nutritional anaemias are extremely prevalent worldwide. Unlike protein-energy malnutrition PEM , vitamin A deficiency and iodine deficiency disorders IDD , these anaemias occur frequently in both developing and industrialized countries.

The most common cause of anaemia is a deficiency of iron, although not necessarily a dietary deficiency of total iron intake. Deficiencies of folates or folic acid , vitamin B 12 and protein may also cause anaemia. Ascorbic acid, vitamin E, copper and pyridoxine are also needed for production of red blood cells erythrocytes. Vitamin A deficiency is also associated with anaemia.

Anaemias can be classified in numerous ways, some based on the cause of the disease and others based on the appearance of the red blood cells. These classifications are fully discussed in medical textbooks. Some anaemias do not have causes related to nutrition but are caused, for example, by congenital abnormalities or inherited characteristics; such anaemias, which include sickle cell disease, aplastic anaemias, thalassaemias and severe haemorrhage, are not covered here.

Based on the characteristics of the blood cells or other features, anaemias may be classified as microcytic having small red blood cells , macrocytic having large red blood cells , haemolytic having many ruptured red blood cells or hypochromic having pale-coloured cells with less haemoglobin. Macrocytic anaemias are often caused by folate or vitamin B 12 deficiencies.

In anaemia the blood has less haemoglobin than normal. Haemoglobin is the pigment in red cells that gives blood its red colour. It is made of protein with iron linked to it. Haemoglobin carries oxygen in the blood to all parts of the body. In anaemia either the amount of haemoglobin in each red cell is low hypochromic anaemia or there is a reduction in the total number of red cells in the body.

The life of each red blood cell is about four months, and the red bone marrow is constantly manufacturing new cells for replacement. This process requires adequate amounts of nutrients, especially iron, other minerals, protein and vitamins, all of which originate in the food consumed.

Iron deficiency is the most prevalent important nutritional problem of humans. It threatens over 60 percent of women and children in most non-industrialized countries, and more than half of these have overt anaemia. In most industrialized countries in North America, Europe and Asia, 12 to 18 percent of women are anaemic.

Although deficiency diseases are usually considered mainly as consequences of a lack of the nutrient in the diet, iron deficiency anaemia occurs frequently in people whose diets contain quantities of iron close to the recommended allowances.

However, some forms of iron are absorbed better than others; certain items in the diet enhance or detract from iron absorption; and iron can be lost because of many conditions, an important one in many tropical countries being hookworm infection, which is very common.

Nutritional anaemias have until recently been relatively neglected and not infrequently remain undiagnosed. There are many reasons for the lack of attention, but the most important are probably that the symptoms and signs are much less obvious than in severe PEM, IDD or xerophthalmia, and that although anaemias do contribute to mortality rates they do not often do so in a dramatic way, and death is usually ascribed to another more conspicuous cause such as childbirth.

However, research now indicates that iron deficiency has very important implications, including poorer learning ability and behavioural abnormalities in children, lower ability to work hard and poor appetite and growth.

To maintain good iron nutritional status each individual needs to have an adequate quantity of iron in the diet. The iron has to be in a form that permits a sufficient amount of it to be absorbed from the intestines.

The absorption of iron may be enhanced or inhibited by other dietary substances. Human beings have the ability both to store and to conserve iron, and it must also be transported properly within the body. The average male adult has 4 to 5 g of iron in his body, most of it in haemoglobin, a little in myoglobin and in enzymes and around 1 g in storage iron, mainly ferritin in the cells, especially in the liver and bone marrow.

Losses of iron from the body must not deplete the supply to less than that needed for manufacture of new red blood cells. To produce new cells the body needs adequate quantities and quality of protein, minerals and vitamins in the diet. Protein is needed both for the framework of the red blood cells and for the manufacture of the haemoglobin to go with it.

Iron is essential for the manufacture of haemoglobin, and if a sufficient amount is not available, the cells produced will be smaller and each cell will contain less haemoglobin than normal. Copper and cobalt are other minerals necessary in small amounts.

Folates and vitamin B 12 are also necessary for the normal manufacture of red blood cells. If either is deficient, large abnormal red blood cells without adequate haemoglobin are produced. Ascorbic acid vitamin C also has a role in blood formation. Providing vitamin A during pregnancy has been shown to improve haemoglobin levels. Of the dietary deficiency causes of nutritional anaemias, iron deficiency is clearly by far the most important. Good dietary sources of iron include foods of animal origin such as liver, red meat and blood products, all containing haem iron, and vegetable sources such as some pulses, dark green leafy vegetables and millet, all containing non-haem iron.

However, the total quantity of iron in the diet is not the only factor that influences the likelihood of developing anaemia. The type of iron in the diet, the individual's requirements for iron, iron losses and other factors often are the determining factors. Iron absorption is influenced by many factors. In general, humans absorb only about 10 percent of the iron in the food they consume. The adult male loses only about 0. On an average monthly basis, the adult pre-menopausal woman loses about twice as much iron as a man.

Similarly, iron is lost during childbirth and lactation. Additional dietary iron is needed by pregnant women and growing children. The availability of iron in foods varies greatly. In general, haem iron from foods of animal origin meat, poultry and fish is well absorbed, but the non-haem iron in vegetable products, including cereals such as wheat, maize and rice, is poorly absorbed. These differences may be modified when a mixture of foods is consumed.

It is well known that phytates and phosphates, which are present in cereal grains, inhibit iron absorption. On the other hand, protein and ascorbic acid vitamin C enhance iron absorption. Recent research has shown that ascorbic acid mixed with table salt and added to cereals increases the absorption of intrinsic iron in the cereals two- to fourfold.

The consumption of vitamin C-rich foods such as fresh fruits and vegetables with a meal may therefore promote iron absorption. Egg yolk impairs the absorption of iron, even though eggs are one of the better sources of dietary iron. Tea consumed with a meal may reduce the iron absorbed from the meal. The normal child at birth has a high haemoglobin level usually at least 18 g per ml , but during the first few weeks many cells are haemolysed. The iron liberated is not lost but is stored in the body, especially in the liver and spleen.

As milk is a poor source of iron, this reserve store is used during the early months of life to help increase the volume of blood, which is necessary as the baby grows. Premature infants have fewer red blood cells at birth than full-term infants, so they are much more prone to anaemia. In addition, iron deficiency in the mother may affect the infant's vital iron store and render the infant more vulnerable to anaemia.

A baby's store of iron plus the small quantity of iron supplied in breastmilk suffice for perhaps six months, but then other iron-containing foods are needed in the diet.

Although it is desirable that breastfeeding should continue well beyond six months, it is also necessary that other foods containing iron be introduced into the diet at this time.

Although most solid diets, both for children and adults, provide the recommended allowances for iron, the iron may be poorly absorbed.

Many people have increased needs because of blood loss from hookworm or bilharzia infections, menstruation, childbirth or wounds. Women have increased needs during pregnancy, when iron is needed for the foetus, and during lactation, for the iron in breastmilk. It is stressed that iron from vegetable products, including cereal grains, is less well absorbed than that from most animal products. Anaemia is common in premature infants; in young children over six months of age on a purely milk diet; in persons infected with certain parasites; and in those who get only marginal quantities of iron, mainly from vegetable foods.

It is more common in women, especially pregnant and lactating women, than in men. In most of the world, both North and South, the greatest attention to iron deficiency anaemia is directed at women during pregnancy, when they have increased needs for iron and often become anaemic. Pregnant women form the one group of the healthy population who are advised to take a medicinal dietary supplement, usually iron and folic acid.

Pregnant and lactating women are a group at especially high risk of developing anaemia. It is only in recent years that the prevalence and importance of iron deficiency apart from anaemia has been widely discussed. Clearly, however, if the causes of iron deficiency are not removed, corrected or alleviated then the deficiency will lead to anaemia, and gradually the anaemia will become more serious.

Increasing evidence suggests that iron deficiency as manifested by low body iron stores, even in the absence of overt anaemia, is associated with poorer learning and decreased cognitive development.

International agencies now claim that iron deficiency anaemia is the most common nutritional disorder in the world, affecting over 1 million people.

In females of child-bearing age in poor countries prevalence rates range from 64 percent in South Asia to 23 percent in South America, with an overall mean of 42 percent Table Prevalence rates are usually considerably higher in pregnant women, with an overall mean of 51 percent. Thus half the pregnant women in these regions, whose inhabitants represent 75 percent of the world's population, have anaemia.

Unlike reported figures for PEM and vitamin A deficiency, which are declining, estimates suggest that anaemia prevalence rates are increasing. In most of the developing regions, and particularly among persons with anaemia or at risk of iron deficiency, much of the iron consumed is non-haem iron from staple foods rice, wheat, maize, root crops or tubers.

In many countries the proportion of dietary iron coming from legumes and vegetables has declined, and rather small quantities of meat, fish and other good sources of haem iron are consumed. In some of the regions with the highest prevalence of anaemia the poor are not improving their dietary intake of iron, and in some areas the per caput supply of dietary iron may even be decreasing year by year.

In many parts of the world where iron deficiency anaemia is prevalent it is due as much to iron losses as to poor iron intakes. Whenever blood is lost from the body, iron is also lost. Thus iron is lost in menstruation and childbirth and also when pathological conditions are present such as bleeding peptic ulcers, wounds and a variety of abnormalities involving blood loss from the intestinal or urinary tract, the skin or various mucous membrane surfaces.

Undoubtedly one of the most prevalent and important causes of blood loss is hookworms, which can be present in very large numbers. The worms suck blood and also damage the intestinal wall, causing blood leakage. Some million people in the world are infested with hookworms. Other intestinal parasites such as Trichuris trichiura may also contribute to anaemia. Schistosomes or bilharzias, which are of several kinds, also cause blood loss either into the genito-urinary tract in the case of Schistosoma haematobium or into the gut.

Malaria, another very important parasitic infection, causes destruction of red blood cells that are parasitized, which can lead to what is termed haemolytic anaemia rather than to iron deficiency anaemia. In programmes to reduce anaemia actions may be needed to control parasitic infections and to reduce blood loss resulting from disease as well as to improve dietary intakes of iron.

Anaemia resulting from folate deficiency is less prevalent than that from iron deficiency or iron loss. It occurs when folate intakes are low and when red cells are haemolysed or destroyed in conditions like malaria.

The anaemia of both folate and vitamin B 12 is macrocytic, with larger than normal red blood cells. Folic acid or folates are present in many foods including foods of animal origin e. Iiver and fish and of vegetable origin e. Vitamin B 12 is present only in foods of animal origin. In most countries vitamin B 12 deficiency is uncommon. Haemoglobin in the red blood cells is necessary to carry oxygen, and many of the symptoms and signs of anaemia result from the reduced capacity of the blood to transport oxygen.

The symptoms and signs are: These symptoms and signs are not confined to iron deficiency anaemia but are similar in most forms of anaemia. Most occur also in some other illnesses and thus are not specific to anaemia. Because none of the symptoms seem severe, dramatic or life threatening, at least in the early stages of anaemia, the disorder tends to be neglected. An experienced health worker can sometimes make a preliminary diagnosis by examining the tongue, the conjunctiva of the lower eyelid and the nailbed, which may all appear paler than normal in anaemia.

The examiner can compare the redness or pinkness below the nail of the patient with the colour beneath his or her own nails. Enlargement of the heart may result and can be detected in advanced severe anaemia. Oedema usually occurs first in the feet and at the ankles. There may also be an increased pulse rate or tachycardia. Occasionally the nails become relatively concave rather than convex and become brittle.

This condition is termed koilonychia. Anaemia is also reported to lead both to abnormalities of the mouth such as glossitis and to pica abnormal consumption of earth, clay or other substances. What is surprising is that many persons with very low haemoglobin levels, especially women in developing countries, appear to function normally.

With chronic anaemia they have adapted to low haemoglobin levels. They may indeed do reduced work, have fatigue and walk more slowly, but they still give the appearance of performing their normal duties even though severely anaemic.

Severe anaemia can progress to heart failure and death. Anaemia, as well as producing the symptoms and signs discussed above, also leads to a reduced ability to do heavy work for long periods; to slower learning and more difficulty in concentration by children in school or elsewhere; and to poorer psychological development. A very important aspect of anaemia in women is that it markedly increases the risk of death of the mother during or after childbirth.

The woman may bleed severely, and she has low haemoglobin reserves. There is also an increased risk for her infant. The diagnosis of anaemia requires a laboratory test. In this respect it differs from the serious manifestations of PEM, vitamin A deficiency and IDD; kwashiorkor, nutritional marasmus, advanced xerophthalmia, goitre and cretinism can all be diagnosed with some degree of certainty by skilled clinical observation.

Consequently, whereas few district hospitals and practically no health centres have laboratories set up to test, for example, levels of serum vitamin A or urinary iodine, most are able to do haemoglobin or haematocrit determinations. These tests require quite cheap apparatus and can be performed by a trained technician, nurse or other health worker.

Determinations of haemoglobin or haematocrit levels are the most widely used in the diagnosis of anaemia. It is now realized that although these tests provide information on the absence, presence or severity of anaemia, they do not provide information on the iron stores of the individual.

In terms of nutritional assessment to guide nutrition planning and interventions, or for research, it may be important to know more about the iron status of an individual than can be gained from haemoglobin and haematocrit determinations. Many methods are used to measure haemoglobin levels.

These range from simple colorimetric tests to more advanced tests which require a proper laboratory. Some new portable colorimeters can be used in the field; they are simple to use and provide reasonably accurate measurements. In the laboratory of even a moderate-sized hospital the so-called cyanmethaemoglobin method is frequently used; it is accurate and can be used to test blood collected by finger prick in the field.

The different methods and their advantages are discussed in various books, of which some are included in the Bibliography. Haematocrit level or packed cell volume PCV , i. Blood also obtained from a finger prick is placed in a capillary tube and centrifuged, usually at 3 rpm.

The centrifuge can be electric run if necessary from a vehicle battery or hand operated. A thin blood film examined under the microscope can be used to judge if the red blood cells are smaller microcytic or larger macrocytic than normal normo cytic. In iron deficiency they are microcytic and in folate or vitamin B 12 deficiency they are macrocytic. Pale cells are termed hypochromic. Cut-off points taken from the World Health Organization WHO suggestions for the diagnosis of anaemia based on haemoglobin and haematocrit determinations are given in Table Certain other laboratory tests are useful in judging iron nutritional status rather than for diagnosing anaemia or its severity.

In recent years it has been increasingly recognized that iron status is important because mild or moderate iron deficiency, prior to the development of anaemia, may adversely influence human behaviour, psychological development and temperature control.

A person whose diet is low in iron or who is losing iron goes through a period when body iron stores which are mainly in the liver are gradually depleted before he or she develops anaemia as judged by low haemoglobin or haematocrit levels see Figure 7. Anaemia is the end stage after iron stores have been depleted. To monitor iron stores it is useful to determine serum ferritin levels, because they are the first to decline.

This is not a simple or cheap test to do, and few small or medium-sized hospitals in developing countries have the ability to do it, but teaching hospitals and nutrition research laboratories sometimes can. Unfortunately serum ferritin levels are influenced by infections, which are common in developing countries. Other determinations that may be done to evaluate iron status and which are described in textbooks include free erythrocyte protoporphyrin FEP and transferrin saturation TS Figure 7.

Suggested criteria for diagnosis of anaemia using haemoglobin Hb and haematocrit PCV determinations. Changes in body iron compartments and laboratory parameters of iron status during development of iron deficiency due to a continuous negative iron balance. The treatment of anaemia depends on the cause. Iron deficiency anaemia is relatively easy and very cheap to treat. There are many different iron preparations on the market; ferrous sulphate is among the cheapest and most effective.

The recommended dose of ferrous sulphate is usually mg providing 60 mg of elemental iron twice daily between meals for adults. Iron tends to make the stools black. Because side-effects can occur, particularly involving the intestinal tract, sometimes people do not take their iron tablets regularly. Slow-release iron capsules have become available and seem to be associated with fewer side-effects. Most capsules contain ferrous sulphate in small pellets, so the iron is slowly released.

Only one capsule or dose needs to be taken each day, but the capsules cost much more than ferrous sulphate tablets. Therefore it is unlikely that slow-release preparations will replace standard ferrous sulphate tablets for use in clinics in developing countries.

New research conducted in China suggests that ferrous sulphate is as effective when given once every week as when given once a day. If further trials confirm this observation, the finding will alter both the treatment of anaemia and the efforts to prevent it using medicinal iron supplements in prenatal clinics. In Indonesia, where vitamin A deficiency is a problem, it has been shown recently that giving vitamin A as well as iron improves the haemoglobin levels of pregnant women more than iron tablets alone.

In all cases the underlying cause of the anaemia should be sought and treated if possible. Iron dextran is the injectable preparation most commonly used. Intravenous injection is preferable. The standing rule is to give a very small test dose initially and to wait for five minutes for any sign of an anaphylactic reaction.

If there is no reaction, then mg can be given from a syringe over a period of five to ten minutes. These injections may be given at intervals over a few days. Alternatively, a total dose infusion can be provided at one time. This procedure must be employed only by doctors experienced in the technique and in calculating dosage levels. It is common during pregnancy to provide folate as well as iron, or combined with iron, as part of the treatment of or prophylaxis against anaemia.

For prevention, where anaemia is prevalent, doses of mg of iron and 5 mg of folate daily are recommended. For treatment of established anaemia, doses of mg of iron and 10 mg of folate are suggested. Successful treatment usually leads to a response in haemoglobin levels within four weeks. Persons with iron deficiency anaemia on very poor diets should be advised to consume more fresh fruits and vegetables at mealtimes.

These foods contain vitamin C, which enhances the absorption of non-haem iron in cereals, root crops and legumes. They also contain folic acid and an array of other vitamins and minerals. If it is feasible and in line with the anaemic patient's budget and culinary habits, he or she could also be advised to consume, even in small quantities, more foods rich in haem iron such as meat, especially liver or kidney. Creating awareness of the nutritional needs of different family members and helping household decision-makers to understand how these needs can best be met from available resources are important steps in preventing iron deficiency.

Iodine deficiency is responsible not only for very widespread endemic goitre and cretinism, but also for retarded physical growth and intellectual development and a variety of other conditions. These conditions together are now termed iodine deficiency disorders IDD. They are particularly important because: In fact, as H.

Labouisse wrote in when he was Executive Director of the United Nations Children's Fund UNICEF , "Iodine deficiency is so easy to prevent that it is a crime to let a single child be born mentally handicapped for this reason" quoted in Hetzel, Nonetheless this crime persists.

Endemic goitre and severe cretinism are the exposed part of the IDD iceberg. These are abnormalities that are visible to the populations where they are prevalent, and they can be diagnosed relatively easily by health professionals without the use of laboratory or other tests. The submerged and larger part of the iceberg includes smaller, less visible enlargements of the thyroid gland and an array of other abnormalities. In many areas of Latin America, Asia and Africa iodine deficiency is a cause of mental retardation and of children's failure to develop psychologically to their full potential.

It is also associated with higher rates of foetus loss including spontaneous abortions and stillbirths , deaf-mutism, certain birth defects and neurological abnormalities. For several decades the main measure used to control IDD has been the iodization of salt, and when properly conducted and monitored it has proved extremely effective in many countries.

It is also relatively cheap. Several international meetings, including the International Conference on Nutrition held in Rome in , called for the virtual elimination of IDD by the year This goal is achievable, provided the effort receives international support and real national commitment in each of the many countries where the disorders remain prevalent. The most important cause of endemic goitre and cretinism is dietary deficiency of iodine.

The amount of iodine present in the soil varies from place to place and this influences the quantity of iodine present in the foods grown in different places and in the water. Iodine is leached out of the soil and flows into streams and rivers which often end in the ocean. Many areas where endemic goitre is or has been highly prevalent are plateau or mountain areas or inland plains far from the sea.

A less important cause of IDD is the consumption of certain foods which are said to be goitrogenic or to contain goitrogens. Goitrogens are "antinutrients" which adversely influence proper absorption and utilization of iodine or exhibit antithyroid activity. Foods from the genus Brassica such as cabbage, kale and rape and mustard seeds contain goitrogens, as do certain root crops such as cassava and turnips.

Unlike goitrogenic vegetables, cassava is a staple food in some areas, and in certain parts of Africa, for example Zaire, cassava consumption has been implicated as an important cause of goitre. Areas of the world where iodine deficiency is prevalent. Any enlargement of the thyroid gland is called a goitre. The thyroid is an endocrine gland centrally situated in the lower front part of the neck.

It consists of two lobes joined by an isthmus. In an adult each lobe of the normal thyroid gland is about the size of a large kidney bean.

In areas of the world or communities where only sporadic goitre occurs or where health workers see only an occasional patient with an enlarged thyroid gland, the cause is not likely to be related to the individual's diet. Sporadic goitre may for example be due to a thyroid tumour or thyroid cancer. However, if goitre is common or endemic in a community or district, then the cause is usually nutritional. Endemic goitre is almost certainly caused by iodine deficiency, and where goitre is endemic other iodine deficiency disorders can also be expected to be prevalent.

Where goitre is endemic, often large numbers of people have an enlargement of the thyroid gland, and some have enormous unsightly swellings of the neck.

The condition is usually somewhat more prevalent in females, especially at puberty and during pregnancy, than in males. The enlarged gland may be smooth colloid goitre or lumpy adenomatous or nodular goitre.

The iodine content of foods varies widely, but the amount of iodine present in common staple foods such as cereals or root crops depends more on the iodine content of the soil where the crop is grown than on the food itself.

Because the amount of iodine in foods such as rice, maize, wheat or legumes depends on where they are grown, food composition tables cannot provide good figures for their iodine content.

Foods from the ocean, including shellfish, fish and plant products such as seaweed, are generally rich in iodine. In many populations, particularly in the industrialized countries of the North and among affluent groups almost everywhere, diets do not depend mainly on locally grown foods. As a result many of the foods purchased and consumed may contribute substantially to iodine intakes. For example, persons living in the Rocky Mountains of North America, where goitre used to be endemic, now do not rely much on locally produced foods; they may consume bread made from wheat grown in the North American central plains, rice from Thailand, vegetables from Mexico or California, seafood from the Atlantic coast and so on.

Similarly, affluent segments of society in La Paz, Bolivia consume many foods not grown in the altiplano, and these imported foods will have adequate quantities of iodine. In contrast, the poor in the Bolivian highlands eat mainly locally grown foods and do develop goitre. Many countries of Asia, Africa and Latin America have major iodine deficiency problems, although some countries have made great progress in reducing the prevalence of IDD.

China and India, with their vast populations, still have a high prevalence of IDD. In the Americas, endemic goitre has been largely controlled in the United States and Canada, but many Andean countries including Bolivia, Colombia, Ecuador and Peru still have relatively high endemic goitre and cretinism rates.

During a survey conducted by the author in the s in the Ukinga Highlands of Tanzania, 75 percent of the people examined had goitre. This was the highest prevalence yet reported in Africa. Prevalence rates of over 60 percent have been reported from communities in many African, Asian and Latin American countries. Generally goitre prevalence rates of 5 to But even with rates of 10 to 15 percent the need for action is important.

Where prevalence rates are moderate, urgent action is needed. Where rates are severe, early action is critical see Table Enlargement of the thyroid gland is the most frequently described and most obvious clinical manifestation of iodine deficiency. Where there is a chronic dietary deficiency of iodine the thyroid often begins to enlarge during childhood, and it becomes more markedly enlarged around the time of puberty, particularly in girls.

In many areas where goitre is endemic the majority of people have some evidence of thyroid enlargement. The thyroid gland secretes hormones vital to metabolism and growth. The gland is made mainly of follicles called acini, minute sacs filled with colloid.

Each sac manufactures thyroid hormones, stores them and secretes them into the bloodstream as needed. The main thyroid hormone is thyroxine. The amount of thyroxine secreted is controlled by another endocrine gland, the anterior pituitary, and its hormone, called thyroid stimulating hormone TSH or thyrotrophic hormone. The function of the thyroid gland is somewhat similar to that of the thermostat of the heating system in a house.

It controls the rate of metabolism and influences the Basal metabolic rate BMR , to some extent the heart rate and also growth in children. The normal adult thyroid gland contains about 8 mg of iodine. In simple goitres the total iodine content might be only 1 or 2 mg even though the gland is larger than normal.

Thyroxine contains 64 percent iodine. A lack of dietary iodine makes it increasingly difficult for the thyroid to manufacture enough thyroxine. The gland enlarges to try to compensate and make more thyroxine.

This enlargement is described by pathologists as a hyperplasia of the gland. It is triggered by increased production of TSH by the pituitary gland.

Microscopic examination of a gland undergoing hyperplasia shows ingrowths or invaginations of the lining epithelium into the normal architecture of the colloid-containing acini.

There is an intense multiplication of cells, with an excess of colloid. This compensatory reaction is an attempt to trap more iodine, and it is partly successful. Many people with colloid goitres show no evidence of poor thyroid function. Investigation of goitre prevalence is one of the most important means of assessing whether there is an IDD problem of public health importance.

Examination of well-chosen samples of schoolchildren has often been recommended as the first step; this survey is relatively easy because schoolchildren are collected together in one place and are usually disciplined, so large numbers can be examined over a short time. To get a full picture of the prevalence in the area, however, it is important at some stage to examine a representative sample of community members of all ages and both sexes. The thyroid gland of each person should be examined both visually and by palpation to judge its size.

Visual examination informs the examiner whether a goitre is visible with the head in normal position or with the head tilted back. Palpation is usually done with the examiner sitting or standing facing the person being examined; the examiner's eyes should be level with the person's neck. By placing and rolling the thumbs on either side of the trachea below the Adam's apple or voice box, the examiner can feel the gland and judge its size.

A normal thyroid gland is considerably smaller than the last joint terminal phalanx of the thumb. In fact a normal thyroid lobe is perhaps one-fifth that size. If each lobe is larger than this joint, then there is a goitre. Palpation from behind is recommended by some because the fingertips are then used to determine gland size, and they are more sensitive than the tips of the thumbs.

It is useful to classify the goitre size using an accepted classification system. Use of the system assures reasonable comparisons by different observers and in different regions. The main use of grading goitres is for survey purposes and to allow comparisons of goitre prevalence rates between areas. It is not possible to be completely objective, and there will seldom be complete agreement between two examiners, but there will be a reasonable measure of agreement.

Persons with goitre are more likely than others to have manifestations of poor thyroid function, especially hypothyroidism. A large goitre, and especially one that enlarges behind the upper part of the sternum, may cause pressure on the trachea and oesophagus, which may interfere with breathing, cause an irritative cough or voice changes and occasionally affect swallowing. A mass in the neck that is consistent with an enlarged thyroid that is palpable but not visible when the neck is in normal position.

It moves upwards in the neck as the subject swallows. Nodular alteration s can occur even when the thyroid is not visibly enlarged. A swelling in the neck that is visible when the neck is in normal position and is consistent with an enlarged thyroid when the neck is palpated.

Moderate and large goitres also create an undesirable appearance and possibly difficulty with wearing certain clothes. It has been reported that in some areas where endemic goitre is highly prevalent, goitres may be accepted as the normal condition or as a sign of beauty and people without a goitre may be considered abnormal. However, in the Ukinga Highlands of Tanzania, where prevalence was over 70 percent, the author found that the people were not pleased to have large neck swellings.

Many people had symmetrical small scars in the skin covering the goitre, which was clear evidence that they had sought local medical treatment; in East Africa treatment frequently consists of cuts and scarification of the offending area, sometimes with herbal medicines rubbed into the cuts. Clearly these people hoped their goitres would disappear. If for any reason too little thyroid hormone is produced, the BMR goes down and a condition called hypothyroidism develops, which may lead to the clinical condition called myxoedema.

In the adult this condition is characterized by coarsened features, dry skin and sometimes puffiness of the face.

The person is often somewhat overweight, has a slow pulse and feels sluggish. Testing would reveal a low BMR and low levels of thyroid hormones in the blood. In contrast, an overactive thyroid gland producing more thyroid hormone than necessary produces a condition known as hyperthyroidism or Graves' disease. The adult with this condition tends to be thin and asthenic, to be nervous and to have a rapid pulse rate, particularly during sleep. Tests reveal high thyroid hormone levels and high BMR.

As stated above, persons with endemic goitre often have good compensation and do not have evidence of either hypothyroidism or hyperthyroidism. They are said to be euthyroid, which means that they have normal thyroid function despite thyroid enlargement. However, in endemic areas rates of hypothyroidism are elevated. In many cases the hypothyroidism is mild and not as obvious as classical myxoedema, but thyroid hormone levels are low, and low BMR, lower productivity and slower mental functioning may be chronic.

It is hypothyroidism in children, however, that is of most concern for developing countries, because of the strong evidence that it causes both mental retardation and slowing of physical growth. Mental retardation ranges from very severe, which is easy to recognize, to mild, which may be difficult to diagnose.

In areas with a high prevalence of IDD large numbers of children may fail to reach their intellectual potential because of impaired school performance and lower IQ than in matched groups from areas without iodine deficiency. These children may later, as adults, fail to make as great a contribution to society and to national development as they would have made if they and their mothers had always consumed adequate amounts of iodine.

Endemic cretinism, including deaf-mutism and mental retardation, begins in infancy. Iodine deficiency in a woman during pregnancy can lead to the birth of a cretinous child. The infant may appear normal at birth but is slow to grow and to develop, small in size, mentally dull, slow to learn and retarded in reaching normal development milestones. Many of these children are deaf mutes. As the child gets older he or she may have the typical appearance of a cretin, which includes a thick skin, coarse features, a depressed nose, a large protruding tongue and frequently strabismus the medical term for eyes that look in different directions, cross-eye or squint.

At two years of age the child may still be unable to walk unassisted, and at three years he or she may not be able to talk or understand simple commands. Cretinism may occur in two forms, namely the neurological form and the hypothyroid form. However, many cretins have some manifestations of both. Features of the neurological form include profound mental deficiency; the characteristic appearance; an inability to walk or a shuffling gait; difficulty in controlling exact movements of the hands and feet spasticity ; and sometimes, but not always, an enlarged thyroid gland.

Signs of hypothyroidism may or may not be obvious. In contrast, the hypothyroid cretin by definition has evidence of low levels of thyroid hormone.

The child usually has a slow pulse, a puffy face and thick skin; is very retarded in physical growth, in bone age and in mental development; and has low BMR. In much of Asia and in South America and formerly in Europe neurological cretinism predominates, whereas in eastern Zaire the myxoedematous form is more widespread.

It is not certain if this occurrence is associated with cassava consumption. In both forms of cretinism the neurological damage, the mental retardation and the dwarfing are not reversible by treatment. Worsening of the condition may be halted, but permanent damage has been done during pregnancy. Therefore the importance of prevention must be emphasized; it is imperative to ensure that women of child-bearing age are not iodine deficient. A consequence of iodine deficiency in communities that is perhaps more important than endemic goitre or overt cretinism is the failure of a large number of persons to grow optimally, either physically or mentally, even though they do not have the classical feature of cretinism.

In some, neurological functioning may also be abnormal. Increasing evidence suggests that iodine deficiency is a major cause of children's failure to reach their intellectual potential, even for those who are not cretins or severely mentally retarded.

School performance may be impaired. Iodine deficiency in an area may have adverse effects on domestic animals as well as humans. Iodine-deficient cattle, goats and poultry may exhibit poor growth and reproduction. The most widely used laboratory test of iodine nutritional status is determination of urinary iodine.

Measurement of urinary iodine excretion should ideally be done on hour urine samples. Relatively few laboratories in developing countries have the equipment or trained personnel to do urinary iodine determinations. This is not a test that ordinary district or even regional hospitals can perform. Other laboratory tests that are used are not measures of iodine status, strictly speaking, but of thyroid function.

Serum thyroxine T 4 is measured and if low is evidence of poor thyroid function, which may be related to goitre. An alternative determination which is increasingly recommended is measurement of blood levels of TSH. In most industrialized countries blood is taken from the umbilical cord or heel of all infants born in hospital and sent on filter paper to a special laboratory for determination of thyroxine or TSH.

This test is done because about one in 4 infants born is hypothyroid because the thyroid gland did not develop properly. If the condition is not diagnosed and treated soon after birth there will be serious consequences, including poor brain development.

Congenital hypothyroidism, however, is not related to IDD. As with urinary iodine, few hospitals in most developing countries are equipped to do T 4 and TSH determinations. Another test of thyroid function is measurement of radioactive iodine uptake levels, usually using I to assess the avidity or "hunger" of the subject's thyroid gland for iodine.

In persons with hypothyroidism caused by iodine deficiency, most of the dose of iodine is taken up by the thyroid gland, and less than 10 percent remains. Some practitioners recommend the use of ultrasonography to produce an image of the thyroid gland, which allows more accurate judgement of the size of the gland than is possible by visual examination and palpation.

Ultrasound is being used increasingly in medicine to examine different organs of the body. It is an attractive method because it is non-invasive and does not involve subjection to X-rays. However, in developing countries ultrasonography will seldom be practical for surveys or for assessing IDD problems. The mental abilities of humans are remarkable compared to other apes.

Humans' ability of speech is unique among primates. Humans are able to create new and complex ideas , and to develop technology, which is unprecedented among other organisms on Earth. Although humans appear hairless compared to other primates, with notable hair growth occurring chiefly on the top of the head, underarms and pubic area , the average human has more hair follicles on his or her body than the average chimpanzee. The main distinction is that human hairs are shorter, finer, and less heavily pigmented than the average chimpanzee's, thus making them harder to see.

The dental formula of humans is: Humans have proportionately shorter palates and much smaller teeth than other primates. They are the only primates to have short, relatively flush canine teeth. Humans have characteristically crowded teeth, with gaps from lost teeth usually closing up quickly in young individuals.

Humans are gradually losing their wisdom teeth , with some individuals having them congenitally absent. Like all mammals, humans are a diploid eukaryotic species. Each somatic cell has two sets of 23 chromosomes , each set received from one parent; gametes have only one set of chromosomes, which is a mixture of the two parental sets.

Among the 23 pairs of chromosomes there are 22 pairs of autosomes and one pair of sex chromosomes. Like other mammals, humans have an XY sex-determination system , so that females have the sex chromosomes XX and males have XY. One human genome was sequenced in full in , and currently efforts are being made to achieve a sample of the genetic diversity of the species see International HapMap Project. By present estimates, humans have approximately 22, genes. The nucleotide diversity between humans is about 0.

By comparing the parts of the genome that are not under natural selection and which therefore accumulate mutations at a fairly steady rate, it is possible to reconstruct a genetic tree incorporating the entire human species since the last shared ancestor.

Each time a certain mutation SNP appears in an individual and is passed on to his or her descendants, a haplogroup is formed including all of the descendants of the individual who will also carry that mutation. By comparing mitochondrial DNA , which is inherited only from the mother, geneticists have concluded that the last female common ancestor whose genetic marker is found in all modern humans, the so-called mitochondrial Eve , must have lived around 90, to , years ago.

Human accelerated regions , first described in August , [] [] are a set of 49 segments of the human genome that are conserved throughout vertebrate evolution but are strikingly different in humans.

They are named according to their degree of difference between humans and their nearest animal relative chimpanzees HAR1 showing the largest degree of human-chimpanzee differences.

Found by scanning through genomic databases of multiple species, some of these highly mutated areas may contribute to human-specific traits. The forces of natural selection have continued to operate on human populations, with evidence that certain regions of the genome display directional selection in the past 15, years. As with other mammals, human reproduction takes place as internal fertilization by sexual intercourse.

During this process, the male inserts his erect penis into the female's vagina and ejaculates semen, which contains sperm. The sperm travels through the vagina and cervix into the uterus or Fallopian tubes for fertilization of the ovum. Upon fertilization and implantation , gestation then occurs within the female's uterus. The zygote divides inside the female's uterus to become an embryo , which over a period of 38 weeks 9 months of gestation becomes a fetus.

After this span of time, the fully grown fetus is birthed from the woman's body and breathes independently as an infant for the first time.

At this point, most modern cultures recognize the baby as a person entitled to the full protection of the law, though some jurisdictions extend various levels of personhood earlier to human fetuses while they remain in the uterus. Compared with other species, human childbirth is dangerous. Painful labors lasting 24 hours or more are not uncommon and sometimes lead to the death of the mother, the child or both.

In contrast, pregnancy and natural childbirth remain hazardous ordeals in developing regions of the world, with maternal death rates approximately times greater than in developed countries.

Females continue to develop physically until around the age of 18, whereas male development continues until around age The human life span can be split into a number of stages: The lengths of these stages, however, have varied across cultures and time periods. Humans are one of the few species in which females undergo menopause. It has been proposed that menopause increases a woman's overall reproductive success by allowing her to invest more time and resources in her existing offspring, and in turn their children the grandmother hypothesis , rather than by continuing to bear children into old age.

Evidence-based studies indicate that the life span of an individual depends on two major factors, genetics and lifestyle choices. Humans are omnivorous , capable of consuming a wide variety of plant and animal material.

In some cases, dietary restrictions in humans can lead to deficiency diseases ; however, stable human groups have adapted to many dietary patterns through both genetic specialization and cultural conventions to use nutritionally balanced food sources. Until the development of agriculture approximately 10, years ago, Homo sapiens employed a hunter-gatherer method as their sole means of food collection.

This involved combining stationary food sources such as fruits, grains, tubers, and mushrooms, insect larvae and aquatic mollusks with wild game , which must be hunted and killed in order to be consumed.

This change in diet may also have altered human biology; with the spread of dairy farming providing a new and rich source of food, leading to the evolution of the ability to digest lactose in some adults. The types of food consumed, and the way in which they are prepared, have varied widely by time, location, and culture. In general, humans can survive for two to eight weeks without food, depending on stored body fat. Survival without water is usually limited to three or four days.

About 36 million humans die every year from causes directly or indirectly related to starvation. No two humans—not even monozygotic twins —are genetically identical. Genes and environment influence human biological variation from visible characteristics to physiology to disease susceptibility to mental abilities. The exact influence of genes and environment on certain traits is not well understood. Most current genetic and archaeological evidence supports a recent single origin of modern humans in East Africa, [] with first migrations placed at 60, years ago.

Compared to the great apes , human gene sequences —even among African populations—are remarkably homogeneous. The human body's ability to adapt to different environmental stresses is remarkable, allowing humans to acclimatize to a wide variety of temperatures, humidity , and altitudes.

As a result, humans are a cosmopolitan species found in almost all regions of the world, including tropical rainforests , arid desert , extremely cold arctic regions , and heavily polluted cities.

Most other species are confined to a few geographical areas by their limited adaptability. There is biological variation in the human species—with traits such as blood type , cranial features , eye color , hair color and type, height and build , and skin color varying across the globe. Human body types vary substantially. The typical height of an adult human is between 1. Adult height for each sex in a particular ethnic group approximately follows a normal distribution.

Those aspects of genetic variation that give clues to human evolutionary history, or are relevant to medical research, have received particular attention. For example, the genes that allow adult humans to digest lactose are present in high frequencies in populations that have long histories of cattle domestication, suggesting natural selection having favored that gene in populations that depend on cow milk.

Some hereditary diseases such as sickle cell anemia are frequent in populations where malaria has been endemic throughout history—it is believed that the same gene gives increased resistance to malaria among those who are unaffected carriers of the gene. Similarly, populations that have for a long time inhabited specific climates, such as arctic or tropical regions or high altitudes, tend to have developed specific phenotypes that are beneficial for conserving energy in those environments— short stature and stocky build in cold regions , tall and lanky in hot regions, and with high lung capacities at high altitudes.

Similarly, skin color varies clinally with darker skin around the equator—where the added protection from the sun's ultraviolet radiation is thought to give an evolutionary advantage—and lighter skin tones closer to the poles.

The hue of human skin and hair is determined by the presence of pigments called melanins. Human skin color can range from darkest brown to lightest peach , or even nearly white or colorless in cases of albinism.

Most researchers believe that skin darkening is an adaptation that evolved as protection against ultraviolet solar radiation, which also helps balancing folate , which is destroyed by ultraviolet radiation.

Light skin pigmentation protects against depletion of vitamin D , which requires sunlight to make. Human skin also has a capacity to darken tan in response to exposure to ultraviolet radiation. Within the human species, the greatest degree of genetic variation exists between males and females. While the nucleotide genetic variation of individuals of the same sex across global populations is no greater than 0.

The genetic difference between sexes contributes to anatomical, hormonal, neural, and physiological differences between men and women, although the exact degree and nature of social and environmental influences on sexes are not completely understood. There is a difference between body types, body organs and systems, hormonal levels, sensory systems, and muscle mass between sexes. Women generally have a higher body fat percentage than men. Women have lighter skin than men of the same population; this has been explained by a higher need for vitamin D which is synthesized by sunlight in females during pregnancy and lactation.

As there are chromosomal differences between females and males, some X and Y chromosome related conditions and disorders only affect either men or women. Other conditional differences between males and females are not related to sex chromosomes.

Even after allowing for body weight and volume, the male voice is usually an octave deeper than the female voice. Women have a longer life span in almost every population around the world. They also have higher circulating clotting factors vitamin K , pro thrombin and platelets. These differences lead to faster healing of wounds and higher peripheral pain tolerance. Additionally, they produce more antibodies at a faster rate than males.

Hence they develop fewer infectious diseases and these continue for shorter periods. One proposed explanation is that human sexuality has developed more in common with its close relative the bonobo , which exhibits similar sexual dimorphism, is polygynandrous and uses recreational sex to reinforce social bonds and reduce aggression.

Humans of the same sex are There is extremely little variation between human geographical populations, and most of the variation that does occur is at the personal level within local areas, and not between populations.

Two randomly chosen Koreans may be genetically as different as a Korean and an Italian. Genetic data shows that no matter how population groups are defined, two people from the same population group are about as different from each other as two people from any two different population groups.

Current genetic research has demonstrated that humans on the African continent are the most genetically diverse. The genetic structure of Africans was traced to 14 ancestral population clusters. Human genetic diversity decreases in native populations with migratory distance from Africa and this is thought to be the result of bottlenecks during human migration.

Only part of Africa's population migrated out of the continent, bringing just part of the original African genetic variety with them. African populations harbor genetic alleles that are not found in other places of the world. All the common alleles found in populations outside of Africa are found on the African continent. Geographical distribution of human variation is complex and constantly shifts through time which reflects complicated human evolutionary history.

Most human biological variation is clinally distributed and blends gradually from one area to the next. Groups of people around the world have different frequencies of polymorphic genes. Furthermore, different traits are non-concordant and each have different clinal distribution.

Adaptability varies both from person to person and from population to population. The most efficient adaptive responses are found in geographical populations where the environmental stimuli are the strongest e.

Tibetans are highly adapted to high altitudes. The clinal geographic genetic variation is further complicated by the migration and mixing between human populations which has been occurring since prehistoric times. Human variation is highly non-concordant: Skin and hair color are not correlated to height, weight, or athletic ability. Human species do not share the same patterns of variation through geography. Skin color varies with latitude and certain people are tall or have brown hair.

There is a statistical correlation between particular features in a population, but different features are not expressed or inherited together.

Thus, genes which code for superficial physical traits—such as skin color, hair color, or height—represent a minuscule and insignificant portion of the human genome and do not correlate with genetic affinity.

Dark-skinned populations that are found in Africa, Australia, and South Asia are not closely related to each other. Despite pygmy populations of South East Asia Andamanese having similar physical features with African pygmy populations such as short stature, dark skin, and curly hair, they are not genetically closely related to these populations.

Due to practices of group endogamy , allele frequencies cluster locally around kin groups and lineages, or by national, ethnic, cultural and linguistic boundaries, giving a detailed degree of correlation between genetic clusters and population groups when considering many alleles simultaneously.

Despite this, there are no genetic boundaries around local populations that biologically mark off any discrete groups of humans. Human variation is continuous, with no clear points of demarcation. There are no large clusters of relatively homogeneous people and almost every individual has genetic alleles from several ancestral groups.

The human brain, the focal point of the central nervous system in humans, controls the peripheral nervous system. In addition to controlling "lower," involuntary, or primarily autonomic activities such as respiration and digestion , it is also the locus of "higher" order functioning such as thought , reasoning , and abstraction.

Generally regarded as more capable of these higher order activities, the human brain is believed to be more "intelligent" in general than that of any other known species. While some non-human species are capable of creating structures and using simple tools —mostly through instinct and mimicry—human technology is vastly more complex, and is constantly evolving and improving through time.

Humans are generally diurnal. The average sleep requirement is between seven and nine hours per day for an adult and nine to ten hours per day for a child; elderly people usually sleep for six to seven hours. Having less sleep than this is common among humans, even though sleep deprivation can have negative health effects. A sustained restriction of adult sleep to four hours per day has been shown to correlate with changes in physiology and mental state, including reduced memory, fatigue, aggression, and bodily discomfort.

In dreaming humans experience sensory images and sounds, in a sequence which the dreamer usually perceives more as an apparent participant than as an observer. Dreaming is stimulated by the pons and mostly occurs during the REM phase of sleep.

Humans are one of the relatively few species to have sufficient self-awareness to recognize themselves in a mirror. The human brain perceives the external world through the senses , and each individual human is influenced greatly by his or her experiences, leading to subjective views of existence and the passage of time.

Humans are variously said to possess consciousness, self-awareness , and a mind, which correspond roughly to the mental processes of thought. These are said to possess qualities such as self-awareness, sentience , sapience , and the ability to perceive the relationship between oneself and one's environment.

The extent to which the mind constructs or experiences the outer world is a matter of debate, as are the definitions and validity of many of the terms used above. The physical aspects of the mind and brain, and by extension of the nervous system, are studied in the field of neurology , the more behavioral in the field of psychology, and a sometimes loosely defined area between in the field of psychiatry, which treats mental illness and behavioral disorders.

Psychology does not necessarily refer to the brain or nervous system, and can be framed purely in terms of phenomenological or information processing theories of the mind. Increasingly, however, an understanding of brain functions is being included in psychological theory and practice, particularly in areas such as artificial intelligence , neuropsychology , and cognitive neuroscience.

The nature of thought is central to psychology and related fields. Cognitive psychology studies cognition , the mental processes' underlying behavior. It uses information processing as a framework for understanding the mind. Perception, learning, problem solving, memory, attention, language and emotion are all well researched areas as well.

Cognitive psychology is associated with a school of thought known as cognitivism , whose adherents argue for an information processing model of mental function, informed by positivism and experimental psychology.

Techniques and models from cognitive psychology are widely applied and form the mainstay of psychological theories in many areas of both research and applied psychology. Largely focusing on the development of the human mind through the life span, developmental psychology seeks to understand how people come to perceive, understand, and act within the world and how these processes change as they age.

This may focus on intellectual, cognitive, neural, social, or moral development. Psychologists have developed intelligence tests and the concept of intelligence quotient in order to assess the relative intelligence of human beings and study its distribution among population. Some philosophers divide consciousness into phenomenal consciousness, which is experience itself, and access consciousness, which is the processing of the things in experience. The concept of phenomenal consciousness, in modern history, according to some, is closely related to the concept of qualia.

Social psychology links sociology with psychology in their shared study of the nature and causes of human social interaction, with an emphasis on how people think towards each other and how they relate to each other. The behavior and mental processes, both human and non-human, can be described through animal cognition , ethology , evolutionary psychology , and comparative psychology as well. Human ecology is an academic discipline that investigates how humans and human societies interact with both their natural environment and the human social environment.

Motivation is the driving force of desire behind all deliberate actions of humans. Motivation is based on emotion—specifically, on the search for satisfaction positive emotional experiences , and the avoidance of conflict. Positive and negative is defined by the individual brain state, which may be influenced by social norms: Motivation is important because it is involved in the performance of all learned responses.

Within psychology , conflict avoidance and the libido are seen to be primary motivators. Within economics, motivation is often seen to be based on incentives ; these may be financial, moral, or coercive. Religions generally posit divine or demonic influences. Happiness, or the state of being happy, is a human emotional condition. The definition of happiness is a common philosophical topic.

Some people might define it as the best condition that a human can have—a condition of mental and physical health. Others define it as freedom from want and distress ; consciousness of the good order of things; assurance of one's place in the universe or society. Emotion has a significant influence on, or can even be said to control, human behavior, though historically many cultures and philosophers have for various reasons discouraged allowing this influence to go unchecked.

Emotional experiences perceived as pleasant , such as love, admiration , or joy , contrast with those perceived as unpleasant , like hate , envy , or sorrow. There is often a distinction made between refined emotions that are socially learned and survival oriented emotions, which are thought to be innate. Human exploration of emotions as separate from other neurological phenomena is worthy of note, particularly in cultures where emotion is considered separate from physiological state.

In some cultural medical theories emotion is considered so synonymous with certain forms of physical health that no difference is thought to exist. The Stoics believed excessive emotion was harmful, while some Sufi teachers felt certain extreme emotions could yield a conceptual perfection, what is often translated as ecstasy.

In modern scientific thought, certain refined emotions are considered a complex neural trait innate in a variety of domesticated and non-domesticated mammals. These were commonly developed in reaction to superior survival mechanisms and intelligent interaction with each other and the environment; as such, refined emotion is not in all cases as discrete and separate from natural neural function as was once assumed.

However, when humans function in civilized tandem, it has been noted that uninhibited acting on extreme emotion can lead to social disorder and crime. For humans, sexuality has important social functions: Sexual desire or libido , is experienced as a bodily urge, often accompanied by strong emotions such as love, ecstasy and jealousy.

The significance of sexuality in the human species is reflected in a number of physical features among them hidden ovulation , the evolution of external scrotum and among great apes a relatively large penis suggesting sperm competition in humans , the absence of an os penis , permanent secondary sexual characteristics and the forming of pair bonds based on sexual attraction as a common social structure. Contrary to other primates that often advertise estrus through visible signs, human females do not have a distinct or visible signs of ovulation, plus they experience sexual desire outside of their fertile periods.

These adaptations indicate that the meaning of sexuality in humans is similar to that found in the bonobo , and that the complex human sexual behavior has a long evolutionary history. Human choices in acting on sexuality are commonly influenced by cultural norms which vary widely. Restrictions are often determined by religious beliefs or social customs. The pioneering researcher Sigmund Freud believed that humans are born polymorphously perverse , which means that any number of objects could be a source of pleasure.

According to Freud, humans then pass through five stages of psychosexual development and can fixate on any stage because of various traumas during the process. For Alfred Kinsey , another influential sex researcher, people can fall anywhere along a continuous scale of sexual orientation , with only small minorities fully heterosexual or homosexual.

Humans are highly social beings and tend to live in large complex social groups. More than any other creature, humans are capable of using systems of communication for self-expression, the exchange of ideas, and organization , and as such have created complex social structures composed of many cooperating and competing groups. Human groups range from the size of families to nations. Social interactions between humans have established an extremely wide variety [ clarification needed ] of values, social norms, and rituals, which together form the basis of human society.

Culture is defined here as patterns of complex symbolic behavior, i. While many species communicate , language is unique to humans, a defining feature of humanity, and a cultural universal.

Unlike the limited systems of other animals, human language is open—an infinite number of meanings can be produced by combining a limited number of symbols. Human language also has the capacity of displacement , using words to represent things and happenings that are not presently or locally occurring, but reside in the shared imagination of interlocutors.

Language is central to the communication between humans, and to the sense of identity that unites nations, cultures and ethnic groups.

The invention of writing systems at least five thousand years ago allowed the preservation of language on material objects, and was a major technological advancement.

The science of linguistics describes the structure and function of language and the relationship between languages.

There are approximately six thousand different languages currently in use, including sign languages , and many thousands more that are extinct. The sexual division of humans into male, female, and in some societies other genders [] has been marked culturally by a corresponding division of roles, norms, practices , dress, behavior, rights, duties , privileges , status , and power. Cultural differences by gender have often been believed to have arisen naturally out of a division of reproductive labor; the biological fact that women give birth led to their further cultural responsibility for nurturing and caring for children.

Gender roles have varied historically, and challenges to predominant gender norms have recurred in many societies. All human societies organize, recognize and classify types of social relationships based on relations between parents and children consanguinity , and relations through marriage affinity. These kinds of relations are generally called kinship relations. In most societies kinship places mutual responsibilities and expectations of solidarity on the individuals that are so related, and those who recognize each other as kinsmen come to form networks through which other social institutions can be regulated.

Among the many functions of kinship is the ability to form descent groups , groups of people sharing a common line of descent, which can function as political units such as clans. Another function is the way in which kinship unites families through marriage, forming kinship alliances between groups of wife-takers and wife-givers.

Such alliances also often have important political and economical ramifications, and may result in the formation of political organization above the community level. Kinship relations often includes regulations for whom an individual should or shouldn't marry. All societies have rules of incest taboo , according to which marriage between certain kinds of kin relations are prohibited—such rules vary widely between cultures.

Rules and norms for marriage and social behavior among kinsfolk is often reflected in the systems of kinship terminology in the various languages of the world.

In many societies kinship relations can also be formed through forms of co-habitation, adoption, fostering, or companionship, which also tends to create relations of enduring solidarity nurture kinship. Humans often form ethnic groups, such groups tend to be larger than kinship networks and be organized around a common identity defined variously in terms of shared ancestry and history, shared cultural norms and language, or shared biological phenotype.

Such ideologies of shared characteristics are often perpetuated in the form of powerful, compelling narratives that give legitimacy and continuity to the set of shared values. Ethnic groupings often correspond to some level of political organization such as the band , tribe , city state or nation. Although ethnic groups appear and disappear through history, members of ethnic groups often conceptualize their groups as having histories going back into the deep past.

Such ideologies give ethnicity a powerful role in defining social identity and in constructing solidarity between members of an ethno-political unit. This unifying property of ethnicity has been closely tied to the rise of the nation state as the predominant form of political organization in the 19th and 20th centuries.

Society is the system of organizations and institutions arising from interaction between humans. Within a society people can be divided into different groups according to their income, wealth, power , reputation , etc. Recognition of the state's claim to independence by other states, enabling it to enter into international agreements, is often important to the establishment of its statehood.

The "state" can also be defined in terms of domestic conditions, specifically, as conceptualized by Max Weber , "a state is a human community that successfully claims the monopoly of the 'legitimate' use of physical force within a given territory.

Government can be defined as the political means of creating and enforcing laws; typically via a bureaucratic hierarchy. Politics is the process by which decisions are made within groups; this process often involves conflict as well as compromise. Although the term is generally applied to behavior within governments, politics is also observed in all human group interactions, including corporate, academic, and religious institutions.

Many different political systems exist, as do many different ways of understanding them, and many definitions overlap. Examples of governments include monarchy, Communist state , military dictatorship , theocracy , and liberal democracy , the last of which is considered dominant today. All of these issues have a direct relationship with economics. Trade is the voluntary exchange of goods and services, and is a form of economics.

A mechanism that allows trade is called a market. Modern traders instead generally negotiate through a medium of exchange, such as money. As a result, buying can be separated from selling, or earning. Because of specialization and division of labor , most people concentrate on a small aspect of manufacturing or service, trading their labor for products.

Trade exists between regions because different regions have an absolute or comparative advantage in the production of some tradable commodity, or because different regions' size allows for the benefits of mass production. Economics is a social science which studies the production, distribution, trade, and consumption of goods and services. Economics focuses on measurable variables, and is broadly divided into two main branches: Aspects receiving particular attention in economics are resource allocation , production, distribution, trade, and competition.

Economic logic is increasingly applied to any problem that involves choice under scarcity or determining economic value. War is a state of organized armed conflict between states or non-state actors. War is characterized by the use of lethal violence against others—whether between combatants or upon non-combatants —to achieve military goals through force. Lesser, often spontaneous conflicts, such as brawls, riots , revolts , and melees , are not considered to be warfare.

Revolutions can be nonviolent or an organized and armed revolution which denotes a state of war. During the 20th century, it is estimated that between and million people died as a result of war. A war between internal elements of a state is a civil war. There have been a wide variety of rapidly advancing tactics throughout the history of war, ranging from conventional war to asymmetric warfare to total war and unconventional warfare.

Techniques include hand to hand combat , the use of ranged weapons , naval warfare , and, more recently, air support. Military intelligence has often played a key role in determining victory and defeat. Propaganda, which often includes information, slanted opinion and disinformation, plays a key role both in maintaining unity within a warring group and in sowing discord among opponents.

In modern warfare , soldiers and combat vehicles are used to control the land, warships the sea, and aircraft the sky. These fields have also overlapped in the forms of marines , paratroopers , aircraft carriers , and surface-to-air missiles , among others. Satellites in low Earth orbit have made outer space a factor in warfare as well through their use for detailed intelligence gathering; however, no known aggressive actions have been taken from space.

Stone tools were used by proto-humans at least 2. Since then, humans have made major advances, developing complex technology to create tools to aid their lives and allowing for other advancements in culture. Major leaps in technology include the discovery of agriculture—what is known as the Neolithic Revolution , and the invention of automated machines in the Industrial Revolution. Archaeology attempts to tell the story of past or lost cultures in part by close examination of the artifacts they produced.

Early humans left stone tools , pottery , and jewelry that are particular to various regions and times. Throughout history, humans have altered their appearance by wearing clothing [] and adornments , by trimming or shaving hair or by means of body modifications.

Body modification is the deliberate altering of the human body for any non-medical reason, such as aesthetics, sexual enhancement, a rite of passage, religious reasons, to display group membership or affiliation, to create body art , shock value, or self-expression. Philosophy is a discipline or field of study involving the investigation, analysis, and development of ideas at a general, abstract, or fundamental level. It is the discipline searching for a general understanding of reality, reasoning and values.

Major fields of philosophy include logic , metaphysics , epistemology , philosophy of mind , and axiology which includes ethics and aesthetics. Philosophy covers a very wide range of approaches, and is used to refer to a worldview , to a perspective on an issue, or to the positions argued for by a particular philosopher or school of philosophy.

Religion is generally defined as a belief system concerning the supernatural , sacred or divine , and practices, values , institutions and rituals associated with such belief. Some religions also have a moral code. The evolution and the history of the first religions have recently become areas of active scientific investigation. Some of the chief questions and issues religions are concerned with include life after death commonly involving belief in an afterlife , the origin of life , the nature of the universe religious cosmology and its ultimate fate eschatology , and what is moral or immoral.

A common source for answers to these questions are beliefs in transcendent divine beings such as deities or a singular God, although not all religions are theistic. Spirituality, belief or involvement in matters of the soul or spirit , is one of the many different approaches humans take in trying to answer fundamental questions about humankind's place in the universe, the meaning of life , and the ideal way to live one's life.

Though these topics have also been addressed by philosophy, and to some extent by science, spirituality is unique in that it focuses on mystical or supernatural concepts such as karma and God. Although the exact level of religiosity can be hard to measure, [] a majority of humans professes some variety of religious or spiritual belief, although many in some countries a majority are irreligious. This includes humans who have no religious beliefs or do not identify with any religion.

Humanism is a philosophy which seeks to include all of humanity and all issues common to humans; it is usually non-religious. Most religions and spiritual beliefs are clearly distinct from science on both a philosophical and methodological level; the two are not generally considered mutually exclusive and a majority of humans hold a mix of both scientific and religious views.

The distinction between philosophy and religion, on the other hand, is at times less clear, and the two are linked in such fields as the philosophy of religion and theology. Humans have been producing art works at least since the days of Cro-Magnon.

Art may be defined as a form of cultural expression and the usage of narratives of liberation and exploration i. This distinction may be applied to objects or performances, current or historical, and its prestige extends to those who made, found, exhibit, or own them.

In the modern use of the word, art is commonly understood to be the process or result of making material works that, from concept to creation, adhere to the "creative impulse" of human beings. Music is a natural intuitive phenomenon based on the three distinct and interrelated organization structures of rhythm, harmony, and melody. Listening to music is perhaps the most common and universal form of entertainment, while learning and understanding it are popular disciplines. Literature, the body of written—and possibly oral—works, especially creative ones, includes prose, poetry and drama, both fiction and non-fiction.

Literature includes such genres as epic , legend, myth, ballad, and folklore. Another unique aspect of human culture and thought is the development of complex methods for acquiring knowledge through observation, quantification, and verification.

All of science can be divided into three major branches, the formal sciences e. From Wikipedia, the free encyclopedia. This article is about humans as a species. For other uses, see Human disambiguation. For the concept of human races, see Race human classification. Man word and Names for the human species. Life timeline and Nature timeline. Homo and Homo sapiens. Anthropology , Human evolution , and Timeline of human evolution.

Archaic human admixture with modern humans , Early human migrations , Multiregional origin of modern humans , Prehistoric autopsy , and Recent African origin of modern humans.

Neolithic Revolution and Cradle of civilization. History of the world. Human migration , Demography , and World population. Basic anatomical features of female and male humans. These models have had body hair and male facial hair removed and head hair trimmed. The female model is wearing red nail polish on her toenails and a ring.

Vitruvian Man , Leonardo da Vinci 's image is often used as an implied symbol of the essential symmetry of the human body, and by extension, of the universe as a whole. Human physical appearance , Anatomically modern human , and Sex differences in humans.

Boy and girl before puberty. Adolescent male and female. Adult man and woman. Elderly man and woman. Childbirth , Life expectancy , and Human development biology. Venus of Willendorf statuette from the Upper Palaeolithic period. Two starved boys during the Russian famine of — Human brain and Mind. Love and Human sexuality. This section needs additional citations for verification.

Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. July Learn how and when to remove this template message. Culture , Society , and Human behavior. Gender role and Gender.

Origins of society , Society , Government , Politics , and State polity. Clothing , Body modification , and Haircut. Philosophy and Human self-reflection. Art , Music , and Literature. This section does not cite any sources.

Please help improve this section by adding citations to reliable sources. March Learn how and when to remove this template message. Human portal Mammals portal. Mammal Species of the World: A Taxonomic and Geographic Reference 3rd ed.

Johns Hopkins University Press. Archived from the original on 7 December Retrieved 14 January Animal Diversity Web UMich. Archived from the original on 5 October Retrieved 25 September Annual Review of Earth and Planetary Sciences. Archived from the original on 26 January Annual Review of Anthropology. In Michael Ruse; Joseph Travis. The First Four Billion Years. Poe A History of Communications: Media and Society from the Evolution of Speech to the Internet.

Cambridge University Press, Ancient History Encyclopedia Limited. Total population both sexes combined by major area, region and country, annually for Medium fertility variant, —". World Population Prospects, the Revision. Archived from the original on 28 July Retrieved 2 October Responsible Science and the Lectotype of Homo sapiens Linnaeus, ". Proceedings of the Academy of Natural Sciences. Archived from the original on 27 September Archived from the original on 25 July Retrieved 25 July Archived from the original on 27 April Retrieved 1 May Archived PDF from the original on 22 May

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