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Micronutrient Deficiency -The Global Situation

This article is adapted from Chapter 3 of the ACC/SCN Second Report on the World Nutrition Situation. Volume I. Global and Regional Results, published October 1992.

Deficiencies in the intake or absorption of vitamin A, iron, and iodine have serious consequences for health and mental and physical function. The clinical manifestations of these nutritional deficiencies - such as xerophthalmia, anaemia, and goitre - have been identified as major problems with increasing public health significance. This article summarizes what is known about trends in micronutrient malnutrition, focussing on these three most prevalent known deficiencies. Estimated prevalences and numbers affected by these three deficiencies are given, by region, in table 1. The distributions by countries are shown in the maps, discussed below.

Vitamin A Deficiency

The most obvious results of vitamin A deficiency are progressive damage to the eye, eventually leading to blindness. The general term for this is “xerophthalmia”, which ranges from the mildest form, night blindness, through reversible signs in the eye, to ulceration and destruction of the cornea, thence blindness. The eye is the most observable tissue damaged by vitamin A deficiency, and progressive damage to other membranes probably occurs, unobserved, in parallel with the eye damage. Increased ill health and mortality have long been associated with vitamin A deficiency, and in recent years intervention trials have established with increasing certainty that providing vitamin A to young children in areas where the deficiency exists, has a significant effect on mortality, of around 25 percent reduction (see article starting on p17). Assessment of vitamin A deficiency is most commonly feasible from clinical signs of eye damage. Dietary surveys and food balance sheet data can also be used to assess the supply of vitamin A in the diet. Vitamin A itself may be preformed in the diet from animal sources, or obtained from carotenes from vegetable sources; the unit, allowing for differential conversion to vitamin A and absorption, is retinol equivalents in mcg.

Table 1. Prevalence of Vitamin A, Iodine and Iron Deficiencies by Region.

Vitamin A Deficiency



Children 0-5 years with xerophthalmia (1991)

All people with goitre (1991)

All women (15-49 years) with low Hb* (around 1988)

WHO Region

No. (millions)


No. (millions)



No. (millions)







Africa (incl. N.)



Eastern Mediterranean







Latin America





Latin America



S.E. Asia (incl. India)





Asia (incl. India & China)



W. Pacific (incl. China)














* Pregnant <11g/dl; non-pregnant <12g.dl.

(Sources: WHO (1992a) & WHO (1990) - quoted in ACC/SCN (1992), tables 3.1 and 3.4 respectively - and WHO (1992b).)

WHO reported that in 1991 nearly 14 million preschool children had eye damage due to vitamin A deficiency (WHO, 1992). Around 10 million of these children are located in Asia. The geographical distribution by WHO regional groupings is given in table 2, and mapped in figure 1. Each year it is estimated that between 250,000 to 500,000 preschool children go blind from vitamin A deficiency. About two-thirds of these children die within months of going blind.

Table 2 Populations at Risk of and Affected by Vitamin A Deficiency, by WHO Region, 1991

(Million pre-school children)

WHO region

Vitamin A deficiency

Total pre-school child population in countries where xerophthalmia exists

Estimated number with xerophthalmia







Southeast Asia






Eastern Mediterranean



Western Pacific






(Source: WHO, (1992a) quoted in: ACC/SCN (1992) Table 3.1, p.40)

The total number of preschool children living in areas where they are at risk of vitamin A deficiency is estimated by WHO at around 190 million. This number increases greatly if other age groups in areas known to be vitamin A deficient are included, such as school age children and women of child-bearing age.

Vitamin A deficiency, defined by eye signs, has been identified as a widespread public health problem in 37 countries worldwide. In countries in which xerophthalmia is endemic, the dietary supply of retinol (mcg/caput/day) estimated from FAO data is often extremely low. Minimum average requirements are around 250 mcg retinol equivalents (RE)/caput/day. As examples, in Mozambique average availability is estimated as 200 mcg RE/caput/day; in Zambia, 290 mcg/caput/day; in Bangladesh, 240 mcg/caput/day. These average supplies are therefore probably below average requirement, making the existence of vitamin A deficiency inevitable in the population. Nonetheless, overall national retinol supply is not always the principal constraint. In 10 of the 37 countries, average supply was above 600 mcg RE/caput/day, and maldistribution of the available supplies is clearly involved. This is particularly the case in those countries - notably in West Africa - that appear to have ample vitamin A because of red palm oil, the production and consumption of which tends to be localized, and not reach deficient areas.

The supply of vitamin A estimated from FAO's food balance sheets indicates an improving trend for most developing countries in the last 20 years, with the notable exception of Sub-Saharan Africa. Countries in the Middle East and North Africa, Middle America and Caribbean, and South America, achieved levels likely to be substantially above average requirements, by the late 1980s. Vitamin A supply is increasing quite rapidly in South East Asia, to the point where it now exceeds average requirements. Vitamin A deficiency persists in this region, but the increase in supply should give potential for redistribution to begin to eliminate the deficiency. In South Asia overall supplies are particularly low, and not rising very fast. This is in line with the observation of quite extensive deficiency in this region, and the slow rate of improvement indicates particular urgency for dietary modification and promotion of consumption of higher retinol-containing diets.

The vitamin A situation in Africa requires closer examination. First, it is essential to distinguish between those countries where red palm oil is produced - in West Africa - and the other countries. East and Southern Africa have very low availabilities of vitamin A, in Southern Africa probably on average below requirement, so that here vitamin A deficiency is likely to be widespread. Added to this, there are some indications that the overall supply is actually decreasing in East Africa, which would exacerbate the problem. In West Africa and the Sahel the apparently high availability does not preclude the co-existence of deficiency. This is related to the fact that red palm oil is not marketed all that widely in a number of these countries.

Iron Deficiency

Iron deficiency is the commonest nutritional disorder in the world and affects over one billion people, particularly reproductive-aged women and preschool children in tropical and sub-tropical zones; it also has a serious impact on school children and working men. If uncorrected it leads to anaemia, reduced work capacity, diminished learning ability, increased susceptibility to infection and greater risk of death associated with pregnancy and childbirth. It results from consuming diets with insufficient bioavailable iron, reduced dietary iron availability, increased iron requirements to meet reproductive demands, and losses due to parasitic infections; these factors often operate concurrently.

Anaemia is thus a serious outcome of iron deficiency. Since there are multiple causes of anaemia, and since iron deficiency can exist without haemoglobin levels being lowered, there are potentially four different situations, or populations: those anaemic and iron deficient; those iron deficient but not (yet) anaemic; those anaemic not due to iron deficiency; and those iron replete and with normal haemoglobin. Causes of anaemia other than iron deficiency often include malaria, intestinal parasites, other nutrient deficiencies such as folate and vitamin B12, and genetically determined haemoglobinopathies such as thalassemia. It is generally held that at least half of the anaemia worldwide is directly due to dietary iron deficiency. On the other hand, there is emerging evidence that low iron stores, even in the absence of anaemia, are also related to functional disadvantages, in cognitive development, learning and behaviour. The extent of this problem has not been widely determined. However, anaemia prevalences are reasonably well established, and can generally be taken as an indicator of the extent and trends of iron deficiency. Here anaemia is assessed by low haemoglobin, with cutoffs determined by WHO. The overall anaemia prevalence for women in developing countries is estimated at 42 percent, equivalent to just over 370 million women; in pregnant women (with a cut off of 11g/dl haemoglobin) the prevalence is estimated at 51 percent, and in non-pregnant women at 41 percent (cut off 12g/dl). While there is considerable variation in prevalence by region - from around 64 percent in South Asia to 23 percent in South America - it is striking that anaemia is prevalent throughout the developing world. The geographical distribution is shown in figure 2, from WHO data. Nearly half the total number of anaemic women are in South Asia.

Figure 1. Geographical Distribution of Xerophthalmia, 1987

(Source: WHO (1987), reproduced in: ACC/SCN (1992), Figure 3.1, p.41)

Figure 2. Prevalence of Anaemia in Pregnant Women, 1988

(Source: WHO (1992b), reproduced in: ACC/SCN (1992). Figure 3.3, p.44)

In the two regions where survey results extend across the last 15 years, Sub-Saharan Africa and South Asia, there are some indications that the prevalence of anaemia is, if anything, increasing (see figure 3). The main types of iron available in foods are: haem iron which is present in meat and its products and is well-absorbed; and non-haem iron which is present from food of vegetable sources, generally of low bioavailability. Iron is also provided by other animal products, such as milk, with intermediate absorption. Isotopic methods of measuring iron absorption from complete meals have increased the knowledge of how these foods are absorbed by the body. Haem iron from meat is highly bioavailable - around 20 to 30 percent being absorbed; whereas non-haem iron from cereals, pulses, fruits, vegetables, etc. has much lower bioavailability - ranging from 1 to 8 percent. The absorption of non-haem iron is highly variable and depends on the nature of the meal. Vitamin C importantly enhances iron absorption. A large number of substances inhibit the absorption particularly of non-haem iron - for example tea, coffee, egg yolk, and bran. Hence it is difficult to interpret the actual availability of iron from overall dietary data. This depends not only on the dietary pattern itself, but also on food habits concerning composition of meals - for example drinking tea with a meal will inhibit iron absorption more than if tea follows the meal.

Figure 3. Trends in Anaemia, 1977-1987 (Nonpregnant adult women, 15-49 years old)

(Source: ACC/SCN (1992). Figure 4.6, p.54)

The overall iron supply is particularly limiting in Sub-Saharan Africa, South Asia, and South East Asia. In these three regions animal sources are low, the average diet is likely to be of low bioavailability, and for many people the supply probably does not reach even the minimum average requirement. This is in line with these regions having the highest estimated prevalence of anaemia. Results from China are inconsistent, and few anaemia estimates are available. In the other regions, the iron supply, particularly taking into account the higher level of animal iron sources, may on average be just adequate; this gives a potential for improvement with redistribution.

More important, perhaps, is the observation that the overall per caput supply of iron appears to be static or perhaps decreasing in all regions except Near East and North Africa. In South Asia this is at least partly due to a major decrease in the production and availability of pulses (lentils, beans, etc.), which have been squeezed out in many areas by the green revolution emphasis on cereal crops. In Sub-Saharan Africa, the decrease may be partly related to a shift away from millets and sorghums; in South East Asia these plus other factors may apply. The diet quality in terms of iron (e.g. as iron/1000kcals) seems to be deteriorating in all regions except Near East/North Africa.

Putting together the results on trends in anaemia (although these are based on rather scanty results) with the dietary iron supply from food balance sheet data, does give a consistent picture, as summarized in table 3. Dietary iron supply trends are deteriorating in most regions, although the average availability may be relatively good in South America because of higher levels of iron from animal sources. The exception, Near East/North Africa, is the one region where indications are that anaemia prevalences are not rising, or possibly even improving. In South America the prevalence of anaemia is probably fairly stable. However, in the other regions, and in particular in Sub-Saharan Africa and South Asia, there are signs that the prevalence of anaemia may be increasing, and this is consistent with the decline in the dietary supply of iron. For regions other than Sub-Saharan Africa this is the one nutrition problem that seems to be getting worse. These results, which no doubt require further investigation, should raise warning flags and shift attention further towards dealing with iron deficiency. At the same time, control of malaria and intestinal parasites must be stressed.

Average iron consumption based on national figures generally hide the distribution across various locations and socioeconomic groups. Recent research on micronutrients indicate that iron consumption behaves differently from other nutrients. It is more income elastic (perhaps the most of major nutrients), owing to the fact that as income increases consumers will purchase more meat and fish. In the Philippines for example, the highest income quintile consumed three to four times more meat and pulses than households in the lowest income quintile. This means that iron consumption overall is likely to be inadequate for poorer households.

Table 3. Regional Trends in Iron Availability and Anaemia (1970-1990)


Trends in Dietary Iron Supply

Trends in Anaemia (non-pregnant Women)

Sub-Saharan Africa

Down slightly, especially from animal sources


Near East/North Africa

Up, from both animal and vegetable sources

Probably down (est. 30% 1975/80. 28% 1985/90)

South Asia

Down, due to reduced pulse production (?)

1 High and increasing

South East Asia

Down slightly, especially vegetable sources from 1980

Probably up (est. 40% 1970-80, 57% 1980-90)

Middle America/Caribbean

Down vegetable sources, but animal sources up

Probably up (est. 20% 1970-80, 30% 1980-90)

South America

Down, but animal sources relatively high

Probably down (est. 24% 1970-80, 20% 1980-90)

(Source: ACC/SCN (1992). Table 3.3, p.47)

Within households, a number of studies show highly disproportionate distribution of iron relative to individual requirements. In the Philippines, adequacy ratios for mothers in three provinces was estimated at 0.65 compared to 1.05 percent for fathers, 0.77 for adolescent girls compared to 0.91 for adolescent boys. While a substantial part of iron adequacy reflects the higher dietary requirements for pregnant mothers and adolescent girls, it is evident that given similar intakes, these sub-groups are likely to suffer most from low availability of iron in the diet due to their different physiological needs. An NNMB 1979 study in India showed that average iron intakes of children 1 to 4 years was 10.2 mg per day, compared to 34.5 mg for adult men, although children have more than half the requirements of adults.

Iodine Deficiency Disorders

Iodine deficiency exists in most regions of the world, resulting from a low intake of iodine in the diet. The consequences of iodine deficiency include goitre, reduced mental function, increased rates of still births and abortions, and infant deaths. Severe mental and neurological impairment known as cretinism occurs in babies with severely iodine deficient mothers. Deficiencies in iodine later in infancy and childhood cause mental retardation, delayed motor development, growth failure and stunting, neuromuscular disorders and speech and hearing defects. Mild deficiency can cause lethargy, and this is reversible when iodine status improves, as is goitre.

The commonest measure of iodine deficiency is from observation of goitre, enlargement of the thyroid gland, usually obtained by specific surveys in iodine deficient regions. Since goitre tends to be localized in such regions, most data are not nationally representative, and thus prevalence estimates are somewhat tentative; trends have not yet been assessed.

WHO* estimates that in 1990 around 1,000 million people lived in iodine deficient environments around the world. These are often regions where the iodine, normally supplied from soil and water, has been leached from the topsoil by rain, flooding, glaciation, and snow. These regions tend therefore to be mountainous and remote, as well as flood plains. In figure 4, areas of iodine deficiency, and the extent of control measures, are shown.

* Very recently these figures were revised, see “News & Views” first article.

The extent of goitre has been estimated (by WHO and ICCIDD) as more than 200 million people, added to which should be around 6 million with overt cretinism. Around half of these are in South East Asia, including India. It is further estimated that some 20 million people worldwide are mentally defective as a result of the deficiency.

Growing international awareness of the problem has led to increased programme and surveillance activities. The problem is largely preventable, and cost-effective methods of eliminating the problem are well known. WHO/UNICEF has declared the goal of eliminating IDD by year 2000, and activities now on-going in collaboration with ICCIDD (International Council for the Control of Iodine Deficiency Disorders).

Control of IDD is mainly through fortification of salt with iodine (salt iodination), and/or periodic distribution of iodized oil, either administered orally or by injection (every three to six months orally, up to two year interval by injection).

Figure 4. Iodine Deficiency Disorders: Areas Affected and Control Programmes, 1991

(Source: WHO (1990), reproduced in: ACC/SCN (1992). Figure 3.6, p.49)

The ICCIDD has summarized the increases in programmes to control IDD. As of 1991, 22 countries were implementing control programmes and another 40 countries were planning to implement action plans. Five years earlier only around six developing countries had IDD programmes in place. Intensified and accurate assessments of the problem, public awareness followed by monitoring and evaluation are essential for reaching the objective of complete elimination of the problem by the end of the century.


WHO (1992a). National Strategies for Overcoming Micronutrient Malnutrition. 45th World Health Assembly Provisional Agenda Item 21; doc A45/17. WHO, Geneva.

WHO (1992b). The Prevalence of Anaemia in Women: A Tabulation of Available Information. Second Edition WHO/MCH/MSM/92.2. WHO, Geneva.

WHO (1990). Infant and Young Child Nutrition, Progress and Evaluation Report. 43rd World Health Assembly document A43/4, agenda item 17, 1 March 1990, page 14.

WHO (1987). The Geographical Distribution of Xerophthalmia in 1987 - Map. Dr E M DeMaeyer. NUT/WHO, Geneva.