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)
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
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