Micronutrients - The Basics
Taken from draft guideline material prepared by Fiona Watson, Institute of Child health, London.
Micronutrients are essential for life and are distinct from macronutrients (carbohydrate, protein and fat) in that they are only required in tiny amounts.
Type I and type II nutrients
An alternative method of classifying nutrients as either type I or type II has recently been proposed (Golden, 1995). This classification is based on the way in which the body responds to a nutrient deficiency. A type I response is characterised by specific physical signs of deficiency as a result of a reduced tissue concentration of the nutrient. For example, if the diet is deficient in a type I nutrient such as iron, there is an initial consumption of body stores followed by clinical signs characteristic of iron deficiency. The concentration of iron in the tissues is markedly reduced, but there is no effect on growth or body weight. In contrast, a type II response is characterised by reduced growth rate or weight loss in the absence of specific deficiency signs. For example, if the diet is deficient in a type II nutrient like zinc, growth stops, followed by weight loss. The concentration of zinc in the major tissues remains normal and their are no deficiency signs. Protein and energy (derived from carbohydrates and fat) are classified as type II nutrients.
The type I and II classification is important because it emphasises that poor growth is not caused solely by protein-energy malnutrition but can result from other nutrient deficiencies which may not be recognised and so appropriately treated. Furthermore, it demonstrates the importance of a wide range of nutrients in causing poor growth or weight loss, and therefore the need for a nutritionally balanced diet.
Micronutrient deficiencies
Micronutrient deficiencies are widespread in developing countries and affect approximately 2 billion people worldwide which is equivalent to one-third of the total world population. The most common deficiencies are due to lack of iron (anaemia), vitamin A (xerophthalmia) and iodine (goitre and cretinism). Outbreaks of deficiency disorders, which are rarely seen in normal circumstances, have also occurred in emergencies among populations entirely dependent on food aid. These include deficiencies of vitamin C (scurvy), niacin (pellagra) and thiamin (beri-beri). The general ration provided in emergencies by agencies like WFP and ICRC are frequently lacking in some essential micronutrients, which means that populations always require other foods (or in some cases micronutrient supplements) to complement the ration. Donor agencies can assist populations to maximise their intake of micronutrient-rich foods by adopting a number of different strategies which, in preferred order, include: promoting the production of vegetables and fruit; providing fresh food items in the ration; adding a food to the ration which is rich in a particular vitamin or mineral; providing fortified foods; and supporting the distribution of nutrient supplements.
| Micronutrient Deficiency diseases | |
| Anaemia | Anaemia can be caused by lack of iron, folate or vitamin B12. It is difficult to diagnose accurately from clinical signs which include pallor, tiredness, headaches and breathlessness. |
| Beri-beri | Beri-beri is caused by thiamin deficiency. There are many clinically recognisable syndromes including wet beri-beri, dry beri-beri and infantile beri-beri. |
| Bitot's spots | Dryness accompanied by foamy accumulations on the conjunctiva, that often appear near the outer edge of the iris, and caused by vitamin A deficiency. |
| Cretinism | Severe mental and physical disability which occurs in the offspring of women with severe iodine deficiency in the first trimester of pregnancy. |
| Goitre | Swelling of the thyroid gland in the neck caused by iodine deficiency. |
| Iodine Deficiency Disorders (IDD) | IDDs cover a range of abnormalities including goitre and cretinism. |
| Night blindness | Inability to see well in the dark or in a darkened room. An early sign of vitamin A deficiency. |
| Pellagra | Pellagra is caused by niacin deficiency which affects the skin, gastro-intestinal tract and nervous systems and is sometimes called the 3Ds: dermatitis, diarrhoea and dementia. |
| Rickets | Rickets is caused by Vitamin D deficiency and adversely affects bone development resulting in bowing of the legs when severe. |
| Scurvy | Scurvy is caused by Vitamin C deficiency. Typical signs include swollen and bleeding gums, and slow healing or re-opening of old wounds. |
| Xerophthalmia | Xerophtalmia is caused by Vitamin A deficiency and refers to a range of eye signs including night blindness, Bitot's spots and corneal ulceration. |
| Micronutrient | Vitamin A | Iron | Iodine | Vitamin C | Niacin | Thiamin | |
| Function | Vitamin A is a fat-soluble vitamin required for the normal functioning of the visual system, growth and development, maintenance of epithelial cell integrity, immune function, and reproduction. | Necessary
for - the synthesis of haemoglobin (Hb), which carries oxygen to the body's cells. Is a component of myoglobin (a muscle protein) and many enzymes. |
- an essential
constituent of hormones produced by the thyroid gland in the neck. - In the foetus, iodine is necessary for the development of the nervous system. |
- a water soluble
vitamin, serves a number of essential metabolic functions. - also assists in absorption of non-haem iron and is an important anti-oxidant. |
- water-soluble and plays a central role in the utilisation of food energy | - water soluble
and is required mainly during the metabolism of carbohydrate, fat and alcohol. - necessary for the proper function of the peripheral nervous system and the heart. |
|
| Source | Retinol is chiefly found in dairy products, liver and some fatty fish. Carotenes are found in yellow and red fruits and vegetables, and in green leafy vegetables, especially the green outer leaves. Vitamin A is absent in vegetable oils with the exception of red palm oil and fortified margarines. | Meat,
cereals, vegetables and fruit Haem- iron: from blood non-haem iron: from vegetables |
- sea food* - small amounts in food dependant on soil iodine content |
- Fresh fruit, fruit juices | - meat (offal),
fish, wholemeal cereals and pulses* - plant and animal foods |
- plant seeds
and yeast* - all animal and plant tissues |
|
| Deficiency | xerophthalmia | Anaemia | range of abnormalities including goitre and cretinism in off spring of deficient mother | scurvy | pellagra | beri-beri | |
| Population prevalence rates to indicate a serious situation | Night blindness
1% Bitot's spot 0.5% Corneal xerosis and/or ulceration 0.01% Xerophthalmia-related corneal scars 0.05% |
Criteria: Anaemia |
(Prevalence
%) 30 and above high risks groups: children and pregnant women |
Goitre above 5% | - no international standards to indicate what prevalence of vitamin C deficiency is a serious situation1 | - no international standards to indicate what prevalence of niacin deficiency is a serious situation1 | - no international standards to indicate what prevalence of thiamin deficiency is a serious situation1 |
| At risk groups | - occurs widely in developing countries with the highest prevalence rates in the regions of South East Asia and Africa. Children suffering from measles, diarrhoea, respiratory infections, chickenpox and other severe infections are at increased risk of vitamin A deficiency | At
risk groups are: · Women of child-bearing age · Pregnant and breastfeeding women · Babies exclusively breastfed beyond the age of 6 months · Babies given cow's milk · Weaning-age children Regions where malaria and intestinal parasitic infestation are prevalent. |
- endemic in
many mountainous areas of Europe, Asia, the Americas and Africa where there
is limited access to sea foods. - prevalence increases with age and reaches a peak during adolescence. - affects girls more than boys and women more than men because of increased activity of the thyroid gland during pregnancy. |
- populations
with no access to fruit or vegetables are at risk of deficiency. - including emergency affected populations entirely dependent on inadequate rations. Scurvy risk higher in women (especially pregnant women) than men and increases with age. |
- maize eating
populations, who do not treat the maize to release niacin, - where legumes, such as peanuts, have not been provided in emergency rations pellagra has arisen. - women are at higher risk than men and risk increases with age. |
Populations who consume non-parboiled polished rice as a staple are at risk, particularly where the rice is contaminated with moulds. | |
1A single confirmed case of scurvy, especially in an emergency situation should be investigated and stimulate a re-assessment of dietary adequacy
*= rich sources
Imported from FEX website