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close this book4th Report on the World Nutrition Situation - Nutrition throughout the Life Cycle (ACC/SCN, 2000, 138 p.)
close this folderCHAPTER 2: MICRONUTRIENT UPDATE
View the document(introduction...)
View the document2.1 Iron Deficiency Update
View the document2.2 Iodine Deficiency Disorders Update
View the document2.3 Vitamin A Deficiency Update
View the document2.4 Multiple Micronutrient Deficiencies
View the documentSummary

(introduction...)

As the life cycle turns, so the risk of micronutrient deficiencies changes. Causes and consequences of early childhood deficiencies have implications for later life and may be present as risk factors for future generations. Severe iron deficiency anaemia during pregnancy may even place a woman’s life at risk during childbirth. Starting with the foetus, iodine deficiency disorders (IDD) may cause brain damage or stillbirth. Folate deficiency of the pregnant woman may result in neural tube defects during foetal development. Iron deficiency anaemia and vitamin A deficiency in the pregnant woman may also have significant implications for the newborn infant, born with low stores. Vitamin A deficiency (VAD) may increase morbidity and mortality risk and affect vision, while anaemia and iodine deficiency disorders may lead to cognitive deficits. Other nutrients are important at certain times in life, such as calcium and folate in adolescence.

The Third Report described the situation of several micronutrient deficiencies in the developing world. While the focus then was primarily on iron, vitamin A, and iodine deficiencies, brief descriptions of the situation with regard to folic acid, zinc, and calcium were also included. A comprehensive review of the programmes to prevent and control these deficiencies was also provided.1 In this Fourth Report, we provide an update of progress in this area during 1998 and 1999, whether in improved knowledge of the nature, causes, or consequences of the problem or in the approaches adopted to deal with it.

We start by using the limited number of recent available surveys to present an update on the prevalence of anaemia as an indicator of iron deficiency and the magnitude of the population at risk of iodine deficiency. Using vitamin A as an example, we illustrate some of the difficulties in estimating the magnitude of the global problem for these three nutrients. While we recognize that other micronutrient deficiencies, such as zinc, are likely to be problems, we offer no estimates of their magnitude or severity as data simply do not exist. There remains a great need for nationally representative data on the prevalence and trends in these deficiencies to inform and improve policy and programme decisions. For each micronutrient, an update is also provided on strategies for the prevention and control of the deficiency. The final section considers the potential of multiple micronutrient supplementation and fortification and the advances being made to realize it.

Data in this chapter refer to stable populations. The micronutrient status of internally displaced people and refugee populations - including the sporadic outbreaks of more uncommon deficiencies such as scurvy, beriberi, and pellagra - is described in Chapter 5.

2.1 Iron Deficiency Update

Iron is essential for the production of haemoglobin, which helps deliver oxygen from the lungs to body tissues, transport electrons in cells, and synthesize iron enzymes that are required to utilize oxygen for the production of cellular energy.2, 3 Iron balance is determined by the body’s iron stores, iron absorption, and iron loss. At least two-thirds of body iron is functional iron, mostly haemoglobin within circulating red blood cells, with some as myoglobin in muscle cells and parts of iron-containing enzymes. Most of the remaining body iron is storage iron (existing as ferritin and haemosiderin), which serves as a deposit to be mobilized when needed.

The reduction of body iron has three main stages: (1) iron depletion, which refers to a decrease of iron stores, measured by a reduction in serum ferritin concentration; (2) iron deficient erythropoeisis, when storage iron is depleted and there is insufficient iron absorption to counteract normal body losses (at this time, haemoglobin synthesis starts to become impaired and haemoglobin concentrations fall); and (3) iron deficiency anaemia, the most severe degree of iron deficiency, which ensues if the haemoglobin concentration falls below a statistically defined threshold lying at two standard deviations below the median of a healthy population of the same age, sex, and stage of pregnancy.4 For every case of iron deficiency anaemia found in a population, there are thought to be at least two cases of iron deficiency.5 A recent report has questioned the current criteria for diagnosis of anaemia and suggested that these be reviewed and revised to link them explicitly to functional outcomes of public health significance.6

Knowledge continues to grow of the very serious functional consequences of iron deficiency anaemia. A recent analysis of the economic consequences of iron deficiency has estimated the median value of productivity losses due to iron deficiency to be about US$4 per capita, or 0.9% of GDP, for a range of developing countries.7 The dominant effect is the loss associated with cognitive deficits in children. This estimate does not include the burden of maternal death associated with severe anaemia, nor the lowered effectiveness of funds spent on education.

Comparing Prevalences and Numbers

Iron deficiency and its anaemia affect more than 3.5 billion people in the developing world.8 While accurate prevalence estimates are difficult to obtain and periodically revised, all public health and nutrition experts agree that this is a huge problem.

To estimate iron deficiency at the global, regional, or national level, anaemia prevalences are used as a proxy indicator. This assumption - namely that iron deficiency is the main cause of anaemia - is likely to hold true in industrialized countries but is less certain in some regions of the developing world where other factors play an important role. These other factors include, for example, malaria and some other parasitic infections, current infectious disease, and other pathologies as well as other nutrient inadequacies that may limit haemoglobin formation. Any estimate of iron deficiency based on anaemia data can thus only be an approximation.

The level of haemoglobin concentration in the blood is used as an indicator to estimate the prevalence of anaemia. Other criteria have been recommended by the Centers for Disease Control and Prevention (CDC) for pregnant women, but these have not yet been adopted and applied on a broad basis. Table 2.1 presents the cut-off points recommended by UNICEF, UNU, and WHO.

Table 2.1: Cut-off points for blood haemoglobin concentration to define anaemia by age group

Age group

g/L

6-59 months

110

5-11 years

115

12-14 years

120

Nonpregnant women

120

Pregnant women

110

Adult males

130

Source: 4.

When global anaemia prevalence is examined for each physiological group, using the WHO Global Database on Anaemia, the most affected groups are pregnant women (48%) and 5 - to 14-year-old children (46%). Preschool children (39%) are also a high-risk group. However, the preschool data should be interpreted cautiously as the prevalence estimates are based on a limited number of surveys, mostly carried out in North and Latin America. Small-scale studies in Africa and Asia have shown higher prevalences for this age group.

Predictably, the prevalence of anaemia in developing countries is three to four times higher than in industrialized countries. The most highly affected population groups in developing countries are pregnant women (56%), school-age children (53%), nonpregnant women (44%), and preschool children (42%). But another group demands attention as well: older adults, half of whom are anaemic (51%).

In industrialized countries, the most-affected groups are pregnant women (18%) and preschool children (17%), followed by nonpregnant women and older adults, both at 12%. The prevalence of anaemia is low for adult males in industrialized countries (5%), but no less than one-third of adult males are anaemic in developing countries (see Figure 2.1). Prevalence estimates are not disaggregated by severity, although such distinctions are increasingly being made in field programmes where the priority is usually to prevent severe anaemia and its high functional costs.


FIGURE 2.1: Prevalence of anaemia by age group in industrialized and developing countries, 1998

Source: 9.

Figure 2.2 presents prevalences by WHO region. (A list of countries in each WHO region appears in Appendix 9.) With regard to preschool children, anaemia prevalence is the highest in Africa and Asia. In Africa the middle part of the continent from the west to the east is the most affected, with anaemia prevalences ranging from 42% to 53%. In Asia the most affected sub-region is South Central Asia. In the Americas the Caribbean is most affected, with a prevalence of 39%, while anaemia prevalences in South and Central America are similar to those observed in the remaining parts of Africa and Asia. Among industrialized countries, anaemia prevalences are lowest in Northern Europe (2%) and around 5% in Western Europe and North America.


FIGURE 2.2: Prevalence of anaemia in children 0-5 years old by WHO region, 1998

Source: 9.

The geographical pattern of anaemia in pregnant women follows that observed for preschool children, with the most affected regions being Africa and Asia (Figure 2.3). In Asia anaemia prevalences are as high as 75% in South Central Asia; in - Africa they range from 47% in Eastern Africa to 56% in Western Africa. In the Americas the prevalence is highest in the Caribbean. In industrialized countries the prevalences range from 14% in Oceania (Australia and New Zealand) to 20% in Eastern Europe.

Finally, although the data for 5 - to 14-year-olds are limited, some estimates can be made. The prevalence of anaemia is highest in South-East Asia (63%) and Africa (52%), followed by the Eastern Mediterranean (45%), the Americas (23%) and the Western Pacific (21%). In industrialized countries, regional prevalences range from 5% in North America to 22% in Europe, including high prevalences in Eastern Europe.

Data on adolescents are scarce. In a multicountry study on adolescent nutritional status carried out by the International Center for Research on Women (ICRW), anaemia was found to be the most widespread nutritional problem and highly prevalent in four of the six country studies in which it was assessed. Prevalences ranged from 32 to 55%; there was no significant gender difference.10 Before the ICRW study, little research had been done on anaemia during adolescence. While girls lose more iron through menses, boys may need more per kilogram weight gained, as relatively more muscle is built during male than female adolescent growth.

With regard to older adults, some data are available from the LSHTM study described in section 1.6. In India, the prevalence of anaemia among people over age 60 was found to be high, using WHO criteria: 38% among men (< 130g/L) and 52% among women (< 120g/L). Among women over 70 years, the prevalence rose to 70%. In both men and women, the prevalence of anaemia was highest among those with severe undernutrition (BMI < 16 kg/m2).


FIGURE 2.3: Prevalence of anaemia in pregnant women by WHO region, 1998

Source: 9.

These are only rough estimates of the global prevalence of anaemia, which need to be refined. Few countries have reported data on anaemia prevalences at the national or sub-national level, so some sub-regions, such as Oceania and Eastern Europe, are poorly covered by the database. Trends could not be assessed anywhere, owing to the lack of repeated, comparable national surveys of anaemia. Moreover, different methods for sampling, assessment, and classification often render data difficult to use. One thing is clear, however: anaemia remains a major problem with serious consequences.

Prevention and Control

A recent joint technical workshop concluded that interventions to control iron deficiency are available, affordable, and sustainable.8 Advances have been made in iron fortification of food staples or condiments and in fortification of complementary foods. A recent review has concluded that iron fortification does not significantly increase the prevalence of iron overload in susceptible individuals, nor the rate at which it develops. These concerns should not constrain the development of iron fortification programmes.11 The use of iron/folate supplements to prevent iron deficiency in malaria-endemic regions has also been endorsed by expert groups.

Nonetheless, in contrast to vitamin A and iodine deficiency control, there remains a significant gap between the efficacy (potential effect) and the effectiveness (actual effect under expected conditions) of programmes aimed at controlling iron deficiency anaemia among highly vulnerable sub-groups such as pregnant women and older infants. Oral iron supplementation programmes are blighted by problems ranging from an inadequate supply of supplements (itself often related to the low priority attached to control of iron deficiency) to poor compliance with their consumption. The UNU/UNICEF/WHO/MI technical consultation recommended better monitoring, evaluation, and research to improve effectiveness.

An authoritative meta-analysis of the efficacy of intermittent iron supplementation was completed in 1999.6 The major findings were that (1) both daily and weekly iron supplementation are efficacious, but weekly supplementation is likely to be less effective than daily administration, except in situations where weekly but not daily supervision is feasible; (2) weekly supplementation may be particularly disadvantageous during pregnancy and in situations where the baseline prevalence of anaemia is high; (3) unless ways are found to greatly improve compliance, neither daily nor weekly supplementation is likely to be an effective approach to preventing and controlling anaemia in developing countries, and (4) regardless of the degree of supervision that can be arranged, weekly iron administration instead of daily is not recommended for pregnancy.

This analysis concludes with a call for applied research to develop other strategies for effectively improving utilizable iron intakes (by altered food usage or food fortification where this is feasible) or for greatly improving compliance in daily or weekly direct supplementation programmes.

One other approach gaining momentum is “self-fortification” through plant breeding, which holds great promise for making a significant, low-cost, and sustainable contribution to reducing micronutrient deficiencies. In this approach, plant breeders seek to take advantage of existing consumption behaviours by developing staple food crops that, in some sense, fortify themselves by loading high amounts of minerals and vitamins into their seeds. One promising variety being tested at the International Rice Research Institute (IRRI) has double the iron (after milling) of standard IRRI releases and is also early maturing, high yielding, and disease resistant. Bioavailability tests using human subjects are planned for 2000. Pending the results of these and other agronomic tests, the new variety may be ready for release to farmers in the Philippines in a few years.12

The development of strategies to control iron deficiency is further hampered by uncertainties concerning its etiology in different situations - particularly in Africa where the non-iron deficiency causes of anaemia may be significant. Working criteria to distinguish the different types of anaemia are needed in order to better define the target groups as well as the most appropriate action. A recently developed tool - the life cycle anaemia risk matrix - may help in organizing etiological assessments, with a view to better determining and prioritizing appropriate control strategies.4

Our understanding of the consequences of iron deficiency has advanced significantly, as has our knowledge of what to do, but our understanding of how to implement appropriate interventions effectively on a large scale is still limited. Research in this area remains an absolute priority. Allied to this, more effective advocacy and communication on the national importance of iron deficiency prevention and control are urgently required.

2.2 Iodine Deficiency Disorders Update

The disorders induced by dietary iodine deficiency (IDD) constitute a major global nutrition concern. The effect of iodine deficiency on the thyroid gland has been known for many decades. Knowledge of the impact of iodine deficiency on mental development has played an important role in mobilizing political leaders, public health officials, nutritionists, and private industry worldwide to launch effective national programmes. Progress towards elimination of IDD through universal salt iodization appears to be one of the most significant successes in the field of non-communicable disease.

Iodine is required for the synthesis of thyroid hormones, which are involved in regulating metabolic activities of all cells throughout the life cycle. In addition, it plays a key role in cell replication. This is particularly relevant for the brain since neural cells multiply mainly in utero and during the first two years of life. IDD comprises all the effects of iodine deficiency. In the foetus these effects lead to increased rates of abortion, still-births, congenital anomalies, cretinism, psychomotor defects, and neonatal mortality. In the child and adolescent, the effects manifest as goitre, hypothyroidism, impaired mental function, retarded mental and physical development, and diminished school performance. In adults, goitre and its complications, hypothyroidism, and impaired mental function persist.13

Median urinary iodine and the prevalence of goitre are the most important indicators for assessing IDD and for describing the severity of IDD as a public health problem. School-age children are the most appropriate target group for IDD surveillance.

Urinary iodine is a marker of very recent dietary iodine intake. The normal population median value of urinary iodine is 100-200 µg/L. Values of 50-99 µg/L suggest mild iodine deficiency, while values of 20-49 and below 20 µg/L suggest moderate and severe iodine deficiency, respectively.14 The benchmark for monitoring progress towards elimination of IDD as a public health problem is 50% of the target group with urinary iodine below 100 µg/L and less than 20% with levels below 50 µg/L.

A goitre is an enlarged thyroid. Thyroid size can be determined clinically by inspection and palpation. Goitre is graded according to size: grade 0 is not palpable or visible; grade 1 is a mass in the neck, consistent with an enlarged thyroid, that is not visible when the neck is in the normal position; and grade 2 is a swelling in the neck that is visible when the neck is in a normal position. Palpation becomes less reliable when average goitre size decreases in a population. Ultra-sonography then provides a more precise and objective method. Ultra-sonography is increasingly used to assess population iodine nutrition, and normative values for thyroid volume measured by ultra-sonography in iodine-replete schoolchildren are needed. The Third Report noted that normative values based on pooled samples of school-children living in Europe had been adopted and were applicable worldwide. This has recently been questioned in light of evidence that some populations of school-age children with adequate median urinary iodine have thyroid volumes much lower than the normative values adopted by WHO. The need for regional scales remains a possibility.15

Finally, elevated serum thyroid stimulating hormone (TSH) in the neonate indicates insufficient supply of thyroid hormone to the developing brain. This is the only indicator that allows prediction of possible impairment of mental development at a population-wide level.

Comparing Prevalences and Numbers

In a joint effort WHO, UNICEF, and ICCIDD recently presented data on the status of IDD at the regional and global levels.16 Of the 191 countries assessed, 130 are affected by IDD (Table 2.2). Of the remaining 61 countries, IDD has been eliminated, or is known not to be present in 20. Data are insufficient for 41 countries, more than half of which are small island states, where IDD is unlikely to be severe. Almost every country in Africa has IDD.

TABLE 2.2: Number of countries affected by IDD, 1999

Region

Total number of countries in region

Countries where IDD is a public health problem

Countries where IDD has been eliminateda or is nonexistent

Countries with insufficient datab

Africa

46

44

1

1

Americas

35

19

3

13

South-East Asia (includes India)

10

9

0

1

Eastern Mediterranean

22

17

1

4

Europe

51

32

13

6

Western Pacific (includes China)

27

9

2

16

Total

191

130

20

41

Source: 16.
a IDD elimination is defined as a total goitre rate (TGR) of < 5% in school-age children.
b Data are insufficient to, categorize countries.

When these figures are transformed into numbers affected by goitre or at risk of IDD (that is, living in a geographical region where the total goitre rate in school-age children is > 5%), it is clear that the scale of the global problem is immense (Table 2.3). Globally about 740 million people are affected by goitre, and more than 2 billion (or over 38% of the population living in 130 countries) are estimated to be at risk of IDD. Many countries - including China and India - have come to regard their entire population as at-risk of IDD.

TABLE 2.3: Current magnitude of IDD, 1999

Population affected by goitre

At-risk population

Region

Populationa (million)

Million

% of regional population

Million

% of regional population

Africa

612

124

20

295

48

Americas

788

39

5

196

25

South-East Asia

1,477

172

12

599

41

Eastern Mediterranean

473

152

32

348

74

Europe

869

130

15

275

32

Western Pacific

1,639

124

8

513

31

Total

5,857

740

13

2,225

38

Source: 16.
a Based on UN Population Division 1997 estimates.

Prevention and Control

Despite the magnitude of the IDD problem, great progress has been made in recent years towards its elimination. The main thrust has been establishing and sustaining national salt iodization schemes. Effective partnerships have been forged between relevant UN agencies, national and international NGOs, and the salt industry. Globally, 68% of households in countries with IDD now consume iodized salt (Table 2.4). Iodization rates are highest in the Americas at 90%. Africa has achieved a level of 63%.

TABLE 2.4: Current status of household consumption of iodized salt, 1999

Region

Number of countries with IDD

Number of countries with a given % of households consuming iodized salt

Overall % of households consuming iodized salt



No data

<l0%

10-50%

51-90%

>90%


Africa

44

8

6

8

19

3

63

Americas

19

0

0

3

6

10

90

South-East Asia

9

0

1

2

5

1

70

Eastern Mediterranean

17

5

1

2

6

3

66

Europe

32

10

4

12

4

2

27

Western Pacific

9

0

1

4

3

1

76

Total

130

23

13

31

43

20

68

Source: 16.

Note: These figures reflect household survey data where this is available; otherwise production-level data are used as a proxy. To estimate the overall iodization rate, total population of each country is multiplied by the per cent of households consuming iodized salt. Numbers are then totaled for each region and divided by the total regional population.

Several national programmes in which the salt industry has exercised leadership have shown spectacular success and made enormous strides towards IDD elimination. In China, for example, most provinces now have over 90% coverage with iodized salt. The national median urinary iodine is 314 µg/L, and all provinces except Tibet have a median concentration greater than 100 µg/L. Adjusted for population, the national total goitre rate is estimated as 10.9% by palpation and 9.6% by ultra-sonography, compared with just over 20% in 1995. The keys to China’s success are effectively iodized salt, enforcement of regulations, strong commitment by government at all levels, an intensive educational programme, and monitoring of salt quality and biological impact.17 China’s success clearly demonstrates how rapid increases in rates of effective salt iodization can increase urinary iodine levels and decrease goitre prevalence.

It takes longer, however, to correct the prevalence of goitre than to correct urinary iodine after the implementation of universal salt iodization, according to a recent study of seven African countries.18 Three countries in the sample (DR Congo, Cameroon, and Nigeria) had a particularly long history of severe IDD. The goitrogenic action of iodine deficiency had been aggravated by the long-term consumption of poorly detoxified cyanide-rich cassava. The national implementation of salt iodization ranged from one year (Tanzania and Zimbabwe) to about five years (Kenya). Two to three areas were visited in each country, and goitre prevalence and median urinary iodine levels were determined in school-age children. Median urinary iodine was above 100 µg/L at all sites visited. This is a major public health success, given the remote location of the sites and their long histories of IDD. The prevalence of goitre had decreased in all sites investigated (compared with the period before salt iodization), but goitre rates were still not below the 5% mark, designated as a criterion for the elimination of IDD.

2.3 Vitamin A Deficiency Update

Vitamin A is an essential micronutrient for the normal functioning of the visual system, growth and development, maintenance of epithelial cellular integrity, immune function, and reproduction.

Clinical deficiency of vitamin A is defined by the presence of night blindness, Bitot’s spots, corneal xerosis and/or ulcerations, and xerophthalmia-related corneal scars. Subclinical deficiency of vitamin A for preschool-age children is defined as the prevalence of serum retinol values < 0.70 µmol/L minus the prevalence of clinical vitamin A deficiency. Among well-nourished, healthy populations of preschool-age children, and even those still living in poverty but whose vitamin A status is adequate, fewer than 5% have values less than 0.70 µmol/L.19

Vitamin A deficiency occurs when body stores are depleted to the extent that physiological functions are impaired. At first, the integrity of epithelial barriers and the immune system become compromised, followed by impairment of the visual system. Consequently, there is increased severity of some infections and an increased risk of death, especially among children. Improving the vitamin A status of young children reduces mortality rates by about 23%, in populations where there is vitamin A deficiency.20 More severe vitamin A depletion leads to night blindness, which can evolve to irreversible partial or total blindness if the depletion continues.19

Comparing Prevalences and Numbers

Estimates of the prevalence of vitamin A deficiency (VAD) in preschool children derived from two separate approaches are presented in Table 2.5. Despite the discrepancies in these estimates, which ultimately reflect the paucity of real data, it is clear that vitamin A deficiency remains a major public health problem of immense proportions.

Some features of the estimated prevalence are important to note. First, since both sets only estimate the number of young children with VAD, these are underestimates of the true magnitude of the global problem. VAD is a significant problem among school-age children and pregnant women in many countries. Data are not available to assess the magnitude of VAD in these groups. Second, the prevalence of VAD is not uniform across countries and regions. WHO estimates that 60 countries have VAD of public health significance.a The MI/UNICEF/Tulane study estimated that 78 countries are affected. The apparent rise in the number of countries affected is more likely the result of improved databases rather than any real trend in prevalence. We lack the data necessary to assess trends in VAD.

a This estimate is based on the occurrence of clinical eye signs or symptoms or very low serum retinol levels (< 0.35 µmol/L).

Clinical VAD, manifest as eye lesions, is decreasing.1 It is not known whether VAD’s impact on severe illness and mortality is decreasing, but with more national surveys and eventual trend estimates for VAD, it should be possible to make reasonable inferences about likely impact on vitamin A - preventable mortality.

Prevention and Control

The available data suggest that there is both an opportunity and a need to target major vitamin A control programmes to particular countries and to particular groups within affected countries. Unlike iodine, VAD is linked more to the nature of foods available and feeding practices than to geo-chemical or other conditions affecting the whole population of geographic areas. Many studies suggest that, like iron deficiency, VAD has strong socioeconomic associations. Indeed, iron deficiency and VAD often coexist in the same sub-populations.

TABLE 2.5: Estimated number of preschool children affected by clinical and subclinical vitamin A deficiency (VAD)

Estimate

WHO/UNICEFa (million)

MI/UNICEF/Tulaneb (million)

Clinical VAD

2.80

3.30

Subclinical VAD

251

75-140

a 21.
b 22.

The great majority of countries where vitamin A deficiency is known to be a major public health problem have policies supporting the regular supplementation of children, an approach of known effectiveness that can reach the sub-populations affected by VAD. Supplementation coverage has increased significantly in the last few years, spurred on by the linkage of supplementation to immunization. Integrating the administration of vitamin A supplements with immunization services, which contact 80% of the world’s children, has been WHO/UNICEF policy since 1994, although progress has been slow and somewhat limited. In contrast, the addition of vitamin A to polio vaccination campaigns has been quick to catch on and is proving to be one of the most successful implementation strategies for reaching large numbers of at-risk children. National Immunization Days (NIDS) offer a ready-made delivery infrastructure and unparalleled reach - in 1997 alone, more than 450 million children were immunized during polio NIDS. In 1998, 88% of the countries where VAD was a moderate to severe public health problem conducted NIDS, two-thirds of which included vitamin A, benefiting more than 24 million at-risk children. This success was the result of a coordinated strategic effort among UNICEF, WHO, major international donors, NGOs, and academic institutions.23

The main limitation of NIDS is that they provide the opportunity for only one dose of vitamin A per year, whereas vitamin A-deficient children need to receive supplements at least twice a year. A minor setback has been the report that coupling vitamin A administration with immunization, while safe, may not have been as effective as had been hoped, at least in terms of reducing mortality.24 Although dramatic progress has been made with supplementation coverage, the NIDS linkage should not be considered a universal panacea, and new approaches must be pursued.

Almost all would agree that food-based approaches (including fortification where feasible) are the logical preferred long-term strategy. There is urgent need to expand fortification efforts where foods reaching the target population groups are processed or where local fortification is feasible. Advances are being made in these areas: fortification of maize is proving successful in Zimbabwe, and the first sugar fortification experience in Sub-Saharan Africa is moving forward in Zambia.23

Approaches based on modified food selection, improved availability of vitamin A-rich foods, and possibly genetic modification of staple foods to enhance vitamin A availability, as with iron, have been slower to develop and more difficult to implement. However, progress is being made. Innovations include the promotion of egg consumption by small children in Indonesia, which has shown promising results.25

The recent finding, however, that the bioconversion of pro-vitamin A in dark green leafy vegetables is less than one-quarter of that previously thought has pointed to one reason why home gardening per se is seldom found to be directly associated with improved vitamin status.26 Home gardening, nonetheless, has other important objectives, such as women’s income generation, and so should be considered a useful complement to a longer-term strategy based on more effective interventions.

Promoting, protecting, and supporting breast-feeding remain essential components of vitamin A control programmes for young children, as does infectious disease control, not only through immunization, but also through complementary hygiene and sanitation interventions.

Finally, there is an urgent need for a good database of nationally representative surveys to help researchers better judge the impact of intervention programmes as well as the magnitude and location of the remaining VAD problem. The inter-agency Global Vitamin A Initiative has recommended as an end-of-2000 goal that all countries with populations affected by vitamin A deficiency or likely to be affected (based on infant and child mortality criteriab) should have a detailed, budgeted plan of action for eliminating vitamin A deficiency as a public health problem.27

b A mortality rate for children under age five of 70 per thousand was proposed by WHO as a possible cut-off for delineating such countries.19

2.4 Multiple Micronutrient Deficiencies

Many population groups in the developing world suffer from multiple nutrient deficiencies. The clustering of iron and vitamin A deficiencies has already been mentioned, but there are many more significant overlaps.

Moreover, deficiencies often interact. Vitamin A supplementation at appropriate levels has been found to improve not only vitamin A status but also iron metabolism in pregnant women and preschool and school-age children.28 It should be considered where iron deficiency is common. A combined iron and vitamin A supplement has been found to be more than 40% more effective in reducing anaemia than an iron supplement alone. Such findings are not specific to supplementation. A vitamin A sugar fortification programme in Guatemala resulted in improved iron status of the population,29 while a trial with vitamin A - fortified MSG in Indonesia increased haemoglobin levels among children.30

Given such frequent overlaps and given the fact that at certain stages of the life cycle - most notably during pregnancy - it may be difficult for dietary needs to be met through diet alone, multiple micro-nutrient supplementation holds clear potential to address multiple nutrient deficiencies in a cost-effective manner. Recent advances have been made in this area since 1998. One publication has addressed key issues concerning the design and implementation of such programmes.31 Also, a joint UNICEF/WHO/UNU workshop was convened in 1999 to consider the composition of a multi-micronutrient supplement to be used in forthcoming trials among pregnant women in developing countries.

Summary

Progress has been made in reducing clinical vitamin A deficiency, but more needs to be done to reduce subclinical vitamin A deficiency, which has significant consequences. The success of salt iodization for controlling iodine deficiency disorders continues to spread; monitoring and sustain-ability are now key concerns. Iron deficiency and its most serious manifestation, anaemia, continue to undermine human potential. Unlike VAD and IDD, there is no clearly effective, widely applicable solution to iron deficiency, though a combination of approaches can make inroads. Operational research remains a major priority, as well as better advocacy for greater attention to combating this invisible scourge.

Overlaps and interactions between micronutrients are likely to be widespread, possibly affecting one in two children with any single deficiency. This fact argues strongly, both operationally and biologically, for multiple micronutrient supplementation and fortification. Such overlaps and interactions undoubtedly occur with regard to micronutrients we know relatively little about.