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Strategies for the prevention of vitamin-a deficiency
Barbara A. Underwood
Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
Each year, thousands of young children go blind or develop impaired vision because of vitamin-A deficiency. Frequently the permanently blinding form of hypovitaminosis A is superimposed on acute protein, and sometimes calorie, deficiency, and often on an infectious disease such as measles. Countless thousands more young children and adults may have their health compromised, in ways difficult to prove, by subclinical hypovitaminosis A that results from an inadequate dietary intake of vitamin-A active foods. Hence, vitamin-A deficiency continues to be a public health problem in many parts of the world- the serious, irreversible forms primarily affecting young children, and the more subtly debilitating form affecting older children and adults as well,
This problem can be prevented and controlled in its public health dimensions by appropriate policies and programmes implemented both nationally and at the community level. But there is no one universally applicable strategy for prevention.
Rather, the most effective strategy must be determined from an evaluation of conditions prevailing and contributing to the etiology locally, as well as of the resources available for prevention through local, national, or international channels wherever the problem exists (1).
There are two basic approaches to prevention. The first is to provide directly for an increased dietary intake of vitamin A; the second is to attack those factors in the environment that decrease the availability of the vitamin from foods and/ or increase the requirement. The two approaches are not mutually exclusive, and where possible should be the combined objective of any strategy for prevention and control of hypovitaminosis A. For the purposes of this presentation, the two approaches and examples of programmes that fall into each category will be discussed separately.
Locally available foods. Nutrition and health education of mothers is a fundamental long-range approach toward solving the problems of both an inadequate intake of the vitamin and increased requirement. In most, though not all, localities where hypovitaminosis A occurs, food sources of provitamin A are available but under-utilized in the diets of the "at-risk" groups. ignorance of the fact that green leaves and vegetables are needed in the diet, and about how they can be appropriately incorporated into the foods of young children, is largely responsible for under-utilization. Taboos and cultural or religious proscriptions on the utilization of these foods are seldom the primary constraint to consumption, although acquired association with a "prestige" value may be a factor. For example, a readily available cheap source of leaves sometimes bears the label of "poor man's" or "animal's" food. Educational programmes implemented by community workers, e.g., agricultural extensionists, community development agents, family-planning implementors, health aides, etc., using very simple messages combined with demonstrations and follow-up visits can effectively increase the intake of locally available, inexpensive foods containing vitamin A, These educational approaches should incorporate equally simple instructions on the sanitary preparation and feeding of these foods. Studies have shown that as little as 15 to 20 grams- a handful- of carotene-rich leaves in a child's daily diet can maintain adequate blood levels and prevent xerophthalmia (2).
There are some geographic areas where hypovitaminosis A exists because there is no available source of foods containing vitamin A. This may be due to inappropriate agricultural planning or to the lack of the necessary environmental conditions to produce such foods. Although theoretically this situation could be most efficiently altered by an increased supply of the pre-formed vitamin found in animal products, it is unlikely, for economic reasons, that this approach would improve the intake of those most at risk of deficiency. As an alternative, increased availability of the usually less expensive plant sources of precursor vitamin A (carotenes) is more apt to improve intake when combined with educational programmes to assure utilization by those most in need (3).
Horticultural improvement programmes may take the form of inter-cropping carotene-rich foods with the more traditional staple crops on the farm land; for example, tomatoes or sweet potatoes (the stem tips as well as leaves are edible) intercropped with corn. Community or school gardens with a priority to produce foods for use in local infant- and child-feeding programmes, and backyard garden production for family use, are other possibilities. Some have calculated that as little as one square yard of land could provide sufficient carotene over a six month harvest period to provide the vitamin-A needs of two young children.
There are, of course, situations in which horticultural approaches at any of the three levels of production are not feasible because of the lack of water, fertilizers, or seeds. In such cases, these constraints could be removed by appropriate agricultural subsidy programmes or community development projects. This emphasizes the need for integration of nutrition and health concerns into overall agriculture and development policies and their adaptation to local situations.
For some, particularly the low-income rural and urban dwellers who depend on the market for food, the cost of food sources of vitamin A is prohibitive when weighed against the need for calorie-dense foods. Studies in some areas show that providing incidental income-generating activities for women is the most effective way to improve the diets of young children (4). Women from these economically marginal families are usually occupied in home and child care as well as in assisting husbands in agricultural activities. Often, however, they can find some time to enter into barter activities for minimal monetary return, and they are likely to use this extra money to provide food for their children. Hence, a development policy that includes a strategy for increased income, including that for women, combined with an educational approach to increase awareness of good child-feeding, can improve the vitamin-A intake from locally available food resources.
Fortification. Vitamin-A fortification of foods or other dietary products, such as condiments and beverages consumed widely by the vulnerable population, can effectively improve the intake of vitamin A at a comparatively low cost. This has been demonstrated by programmes currently under way in several countries (5).
At times a narrow view toward fortification of a single food item on a national scale limited the options considered, because an appropriate single food centrally processed and consumed by children as well as adults could not be identified. Before abandoning this alternative, thought should be given to regionalization in the search for a variety of alternatives, and to the feasibility of a decentralized, community-level fortification programme. Such a programme does complicate the logistics, including those of monitoring, to assure that the quantity supplied is sufficient but not excessive so that there is minimal risk of toxicity from over-consumption.
Direct vitamin supplements. This approach toward augmenting the dietary intake of vitamin A has been tested in several countries. There is no doubt about its effectiveness in reducing the prevalence of xerophthalmia in those who receive periodic, concentrated dosing, but there is uncertainty about how long the interval between closings should be to assure efficacy and affordability (6, 7). There is also the question of whether this approach alone is adequate to prevent keratomalacia when acute protein-energy malnutrition (PEM) occurs concurrently (8). Evidence is amassing that the acute dietary protein deficit must be corrected concomitantly with vitamin-A deficiency to assure the physiological availability of the vitamin to deficient tissues.
It has not yet been proved that mild or moderate PEM critically limits vitamin-A utilization (9). As a public health measure to reduce the prevalence of xerophthalmia and subclinical vitamin A deficiency, periodic dosing with concentrated supplements can be effective, but to prevent keratomalacia, programmes may need to be targeted to the acutely protein-energy malnourished child who is then provided protein as well as the vitamin.
Perhaps the best use of direct vitamin supplementation programmes is to channel them through medical institutions, the health network, and community aides that reach not only the high-risk, acutely ill, but also pregnant and lactating mothers and young children, all of whom have elevated requirements Those making the vitamin supplement available must be trained to recognize the conditions and signs associated with deficiency, and have frequent direct contact with mothers and their children. A prevention strategy would have to include the training of this type of personnel to identify problems and to provide various solutions.
Safeguards are needed, especially in programmes that rely on auxiliary or paramedical personnel for delivery. For these workers, dosages in the range of 25,000 to 50,000 I.U. would be safe and appropriate, as they see the at-risk individuals on a more frequent schedule and can give the supplement more often. The effectiveness of a targeted approach will be determined by the provider's recognizing both the ecologic and physiologic factors generally associated with a high risk of deficiency, and the clincial ocular evidence of a deficiency state.
Improved efficiency of absorption. Efficient fat absorption is important for adequate absorption of pre-formed vitamin A, and especially absorption of carotenes. This assumes that there is sufficient fat in the diet and that it is effectively hydrolysed in the gut to facilitate the formation of watermiscible, mixed lipid micelles that act as solubilizers and carriers of the water-insoluble vitamin. Dietary fat requirements are not known, but some studies suggest that diets containing less than 5 grams daily are associated with a reduced absorption of carotenes (2). The diets of many preschool children are thus low in fat, and furthermore, these children often rely almost exclusively on a limited dietary supply of carotenes to meet their vitamin-A needs. Whereas dietary fat may not be limiting to the absorption of pre-formed vitamin A given either in the diet or as capsule supplements, it may become limiting in diets marginal in carotenes. In these situations, a strategy to improve the consumption of fat by the at-risk children may be appropriate to improve carotene absorption. This would have the added benefit of increasing the caloric density of the diet as well.
Dietary protein also facilitates absorption of carotenoids by assuring sufficient precursors for the synthesis of digestive enzymes and the mucosal carotene, dioxygenase, as well as for maintenance of a healthy mucosal surface.
CONTROL OF INFECTIONS THROUGH PUBLIC HEALTH INTERVENTIONS
Public health interventions offer several advantages because most improve the general quality of life in the community. Those aimed at control of enteric and systemic infections through improved sanitation and immunization will not bring about the immediate, impressive changes in the vitamin-A status of a population offered by a direct increased intake of vitamin A through a supplementation programme. However, public health measures will lead to an incremental improvement, and where possible should be part of any long-range strategy for prevention.
Furthermore, there is some evidence that local or generalized infection may directly or indirectly be one of the factors, along with acute protein deficiency, causing keratomalacia in a vitamin-A-deficient subject.
Selection of a Strategy for the Prevention of Hypovitaminosis A
Several possible approaches toward prevention have been mentioned. The strategy selected and the specific programmes that comprise it will depend upon the seriousness and magnitude of the problem, its relationship to other health needs, and the objectives for prevention within national health, food, nutrition, and development goals (1). It is essential that the objectives and goals for a hypovitaminosis-A prevention strategy be agreed upon at the highest levels of national planning. Programme success will depend not only upon the effectiveness of implementation within and by communities, but also on the political commitment to support such programmes with scarce resources for which there are usually many competing needs.
Where clinical signs of xerophthalmia are prevalent at rates near or above the level that WHO suggests is a public health problem (11), the immediate objective might be: (a) to control xerophthalmia and eliminate related blindness as a public health problem, or (b) to improve the vitamin-A status of populations at high risk of developing xerophthalmia. While both objectives require an immediate increased intake of vitamin A, the target population and numbers to be treated vary. For example, the first objective calls for a programme targeted to young children, especially those with clinical PEM and associated acute infections. The second objective would include this same population as well as underprivileged but not acutely ill children;, and pregnant and lactating women.
A third objective for a national programme where clinical signs are less prevalent might be to improve the level of vitamin-A nutrition of the population as a whole. This is an appropriate objective on which to base programmes even where the prevalence of xerophthalmia is not high, but where there is evidence of inadequate vitamin-A intakes. From parallels in animal models, we can assume that there are non visual health consequences of hypovitaminosis A. The decision to initiate an intervention strategy based on this objective, however, is largely a political one. Although a large segment of an underprivileged population might be in a pre-clinical state of hypovitaminosis A as well as deficient in other dietary nutrients, it will be difficult to document to what extent health might be improved by increased vitamin A intake alone.
The long-term goal of a strategy to prevent vitamin-A deficiency is, broadly defined, to provide all people with a diet adequate in the vitamin and other nutrients that interact in vitamin-A metabolism. WHO has compiled a list of 73 countries whose populations are likely to have an inadequate level of vitamin A to a degree worthy of immediate public health attention. Obviously, a general upgrading of the level of development in these countries and a more equitable distribution of the benefits of development, including income, would substantially reduce the magnitude of the problem. We cannot wait for this to occur while the irreversible consequences of acute deficiency of vitamin A accrue. Hypovitaminosis A is amenable to solution through public health programmes that need not await overall development. Where the serious, irreversible forms of visual impairment are prevalent, appropriate intervention programmes should be instituted immediately. Where milder forms exist, and where resources are available, earnest consideration should be given to improving vitamin-A nutrition for the general population as well. A global political commitment is needed for the eradication of hypovitaminosis A as a public health nutrition problem.
1. B.A. Underwood, "Hypovitaminosis A and Its Control," Bull. World Hlth. Org., 56 (1978).
2. S.M. Pereira and A. Begum, "Vitamin A Deficiency in Indian Children," World Rev. Nutr. Dietet., 24: 192 (1976)
3. A. Pirie "The Role of Carotene in Prevention of Xerophthaimia," Baroda J. Nutr., 2:79 (1975).
4. R.B. Tripp, "Economic Strategies and the Nutritional Status of Children in Northern Ghana" (Ph.D. dissertation Department of Anthropology, Columbia University, New York, 1978).
5. G. Arroyave, J.R. Aguilar, M. Flores; and M.A. Guzman, "Evaluation of Sugar Fortification with Vitamin A at the National Level," PAHO Scientif. Publ. 384 11979).
6. S.M. Pereria and A. Begum, "Failure of a Massive Single Oral Dose of Vitamin A to Prevent Deficiency," Arch. Dis Childh., 46:525 (1971).
7. D.P. Sinha and F.B. Bang, "The Effect of Massive Doses of Vitamin A on the Signs of Vitamin A Deficiency in Preschool Children," Amer. J. Clin. Nutr., 29: 1 10 (1976).
8. G. Venkalaswamy, J. Glover, M. Cobby, and A. Pirie, "Retinol-binding Protein in Serum of Xerophthalmic, Malnourished Children Before and After Treatment at a Nutrition Center," Amer. J. Clin. Nutr., 30: 1968 (1977).
9. V, Reddy, M. Mohanram, and N. Raghuramulu, "Serum Retinol-binding Protein and Vitamin A Levels in Malnourished Children," Acta Poedist. Scand., 68: 65 (1979).
10. F. Solon, T.L. Fernandez, M.C. Latham, and B.M. Popkin, "An Evaluation of Strategies to Control Vitamin A Deficiency in the Philippines," Amer. J. Clin. Nutr., 32: 1445 (1979).
11. World Health Organization, "Vitamin A Deficiency and Xerophthalmia: Report of a Joint WHO/USAID Meeting." WHO. Tech. Rep. Series 590 (WHO, Geneva, 1976).
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