Micro­nutrients – Vitamins and Minerals

Vitamins and minerals are called micronutrients. They are needed in much smaller amounts than protein, fat or carbohydrates, but are essential for good nutrition. They help the body to work properly and stay healthy. Some minerals also make up part of the body tissue: calcium and fluoride are found in bones and teeth, and iron is found in the blood.

Vitamins

Vitamins are substances present in very small amounts in foodstuffs, which are necessary for metabolism, normal growth, and the maintenance and repair of body cells. The group is divided into water-soluble and fat-soluble vitamins.

  • Water-soluble vitamins Vitamin C and the B vitamins are water-soluble. These vitamins are quickly absorbed into the blood and body cells. Excess amounts of these vitamins are not stored by the body, but are passed out in the urine. Therefore we need to include food sources of these vitamins in our daily food intake.
  • Fat-soluble vitamins Vitamins A, D, E and K are fat-soluble vitamins. These vitamins are absorbed into the cells of the body very slowly. Excess amounts of these vitamins are stored in the liver to meet later needs.

Vitamin A

Vitamin A deficiency (VAD) is the leading cause of preventable blindness in children, and increases the risk of disease and death from severe infections. In pregnant women, VAD causes night blindness and may increase the risk of maternal mortality[1]. In developing countries, vitamin A deficiency typically begins during infancy, when infants do not receive adequate supplies of colostrum (the thick, yellowish milk produced the first few days after the birth of the baby) or breast milk. Chronic diarrhoea also leads to excessive loss of vitamin A in young children, while vitamin A deficiency in turn increases the risk of diarrhoea.

Food sources of vitamin A

Vitamin A is found naturally only in foods of animal origin, notably breast milk, liver, eggs, milk and many dairy products. However, many dark-coloured fruits and vegetables contain pigments (called carotenes) that the body can convert to vitamin A. Foods rich in carotene include carrot, pumpkin, green leafy vegetables like spinach and watercress, deep yellow and orange sweet potatoes, mangoes when in season and apricots.

Vitamin D

The function of vitamin D in the body is to allow the proper absorption of calcium. Likewise, vitamin D stores in the body are affected by low calcium from the diet. Lack of vitamin D is associated with the disease rickets, characterised by deformity (bowing) of the arms and legs. In adults, especially post-menopausal women, lack of calcium and vitamin D can lead to osteoporosis, a condition which increases the risk of bone fractures in the elderly. A growing body of research shows that vitamin D may be beneficial in preventing heart disease, some cancers, osteoporosis, as well as infectious diseases, such as tuberculosis and even seasonal influenza[2].

Sources of vitamin D

In human beings, vitamin D can either be made in the skin from a cholesterol-like precursor by exposure to sunlight or be obtained preformed from foods. Both forms of vitamin D behave in the same way in the body.

Vitamin D occurs naturally only in very few foods, such as in the fat of certain animal products. Eggs (especially egg yolk), fatty fish and fish-liver oils, and certain types of mushroom are good sources in normal diets. Meat and dairy products contribute small quantities. Cereals, vegetables and fruit contain no vitamin D.

Sun exposure is the main source of vitamin D, but excessive sun exposure is also the main cause of skin cancer, including melanoma. Enjoying the sun safely, while taking care not to burn, can help to provide the benefits of vitamin D without unnecessarily raising the risk of skin cancer.

Covering up the skin increases women’s and children’s risk of vitamin D deficiency. The World Health Organization recommends 5 to 15 minutes of sun exposure of hands, face and arms two to three times a week, which is sufficient to keep vitamin D levels high[3]. Closer to the equator, where UV levels are higher, even shorter periods of exposure may be sufficient.

Vitamin B complex                 

Thiamin, riboflavin, niacin, vitamin B6, folate, pantothenic acid, vitamin B12 and biotin belong to what is sometimes called the vitamin B complex. One of the most important B vitamins is folate.

Folate (vitamin B9, folic acid) is needed to make healthy blood cells. Folate deficiency during pregnancy can lead to birth defects.

Food sources of folate

The richest sources of folate are liver and kidney. Egg yolk, dark green leaves, oranges, brown rice and chickpeas are also good sources. Other vegetables and meats contain smaller amounts.

Vitamin C is needed to increase absorption of iron from food, to make collagen (connective tissue) that binds the body’s cells together, and to serve as an antioxidant[4]. Prolonged vitamin C deficiency can lead to scurvy, which occurs periodically in remote regions of Afghanistan especially during the winter months when fresh vegetables and fruit may not be available. The signs of scurvy are bleeding gums and sore, swollen joints. Scurvy can lead to death.

Food sources of vitamin C

Most fruits, especially citrus fruits like lemon, orange and sweet orange, as well as fruits like strawberries and guava, are sources of vitamin C. Many green leafy vegetables, including garden cress, spinach and gourd/radish leaves, as well as green peppers, tomatoes and lady’s fingers are good sources of vitamin C too. However, vitamin C is easily destroyed by heat; prolonged cooking of vegetables may destroy most of the vitamin C present. Eating fresh fruit and vegetables is important.

Minerals

Minerals are chemical substances found in food, needed by the body in very small amounts for growth and development. Some important minerals are calcium, iron, iodine, fluorine and zinc.

Iron

Iron is essential for transporting oxygen to various sites in the body as needed. Iron deficiency can lead to anaemia. Iron deficiency anaemia can be due to various reasons: low iron content in the diet; the body not absorbing the iron properly; or due to excessive blood loss. For example, hookworm infections, which are common in many countries, result in loss of blood which may cause anaemia. Women with heavy menstrual losses can lose a significant amount of iron and are at considerable risk of iron deficiency.

Women of childbearing age, pregnant women, infants and young children have the greatest need for iron. Signs of iron deficiency anemia include feeling tired and weak, decreased work and school performance, slow mental development during childhood, and increased susceptibility to infection. Iron deficiency among pregnant women can damage the brain development of their fetus and so the newborn may suffer physical growth and mental development problems. Studies indicates that iron deficiency among children during the first 1000 days of life is associated with a loss of 10 scores in IQ ( a measure of mental development) and these children will lag behind in performance in the school.

Food sources of iron

Food sources containing haem iron are the best for increasing or maintaining healthy blood iron levels. Such foods include organ meats, beef, lamb, poultry and fish.

Non-haem iron, from cereals and vegetables, is less well absorbed by the body. Eggs, dairy products, legumes and nuts, and vegetables, such as spinach, all contain iron, but in the non-haem form, which is not well absorbed.

Tea and coffee inhibit the absorption of iron, and should not be taken for two hours before or after a meal with iron containing foods. Iron absorption can be increased by combining foods from different food groups, for example, by adding a little animal source foods, especially meat, to plant foods; and by eating iron-rich foods together with vitamin C-rich foods.

Iodine

Iodine is needed for the proper function of the thyroid gland, and for the normal growth and development of children, including their development. Iodine deficiency is the most common cause of preventable mental retardation in the world. In pregnant women, iodine deficiency can cause birth defects and growth retardation in the foetus, as well as miscarriage and stillbirth. Enlargement of the thyroid gland, called a goitre, is one of the visible signs of iodine deficiency.

Children with iodine deficiency cannot develop their development potentials. The IQ scores will be lower by 10-15 scores and probability of leaving school unfinished is high. This developmental consequences of iodine deficiency is not more a source of concern in public health and therefore universal salt iodization program has been introduced in many countries of the world.

Food sources of iodine

Iodine is widely present in rocks and soils. The quantity in different plants varies according to the soil in which they are grown. Iodine tends to get washed out of the soil, and throughout the ages a considerable quantity has flowed into the sea. Sea fish, seaweed and most vegetables grown near the sea are useful sources of iodine. Drinking-water provides some iodine but very seldom enough to satisfy human requirements. In Afghanistan, salt iodization has been mandatory since 2010. Salt with iodine added is available in shops, and should be used.

Zinc

Zinc is an essential mineral, and plays a role in immune function, protein synthesis and wound healing. Zinc deficiency in children is associated with increased illness and death from diarrhoea. In pregnant women zinc deficiency may result in the foetus not growing well, leading to low birth weight babies.

Food sources of zinc

The richest sources of zinc tend to be protein-rich foods such as meat, seafood and eggs. Other good sources of zinc are beans and nuts, however, as with iron, only relatively small amounts of zinc from plant foods can be absorbed by the body.

Sodium/Salt

Too much sodium is harmful and can lead to high blood pressure (hypertension) in some people, which is associated with strokes and heart disease. Most people obtain the greatest part of their sodium from salt (sodium chloride), which can be added in cooking, added at the table, added in processing (for example, in sausages and in tinned fish canned in brine), or found in foods processed in some manner, such as cheese. However, as mentioned before, iodized salt is an important source of iodine. Only a small amount of salt is needed from food to maintain health. The recommended intake of salt is 5 grams of salt per day (2.5 g sodium).

[1] WHO, 2014. http://www.who.int/nutrition/topics/vad/en/

[2] Harvard School of Public Health Nutrition Source: Vitamin D and Health http://www.hsph.harvard.edu/nutritionsource/vitamin-d/

[3] http://www.who.int/uv/faq/uvhealtfac/en/index1.html#

[4] Substances with disease fighting properties that protect cells from damage by other substances called free radicals. Examples of dietary antioxidants include beta-carotene, lycopene, and vitamins A, C and E.

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