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Influence of Vitamin A on Iron Status and Consequences for <strong>Micronutrient</strong> Deficiency Alleviation Programs Table 1. Prevalence of vitamin A deficiency among selected population groups in Indonesia Population Group n Criterion Prevalence (%) Reference National survey:
Vitamin A deficiency has long been known to be the main cause of childhood blindness in developing countries (Sommer 1982). However, even subclinical vitamin A deficiency has broader consequences in terms of childhood morbidity and mortality. Several reports over the past decade have shown that vitamin A deficiency is also associated with increased mortality and an increased severity of infectious diseases (Beaton et al. 1993, Sommer et al. 1986, Sommer et al.1984). The Association Between Iron and Vitamin A The metabolism of iron and vitamin A is associated in that vitamin A status influences iron metabolism (Bloem 1995). In the first half of this century, several studies suggested that a lack of vitamin A in humans and experimental animals may result in anemia (Wagner 1940, Frank 1934, Blackfan and Wolbach 1933, Sure et al. 1929, Koessler et al. 1926, Wolbach and Howe 1925, Findlay and MacKenzie, 1922). More recently, crosssectional studies in children (Wolde-Gabriel et al. 1993, Bloem et al.1989, Mejia et al. 1977) and pregnant women (Suharno et al.1992) showed associations between retinol and indicators of iron status. These cross-sectional studies were followed-up by intervention studies that showed that increased intake of vitamin A may lead to an improvement in iron status (Table 2). The information in Table 2 shows that vitamin A supplementation affected iron status and that iron supplemented in combination with vitamin A had a greater effect than iron supplemented alone. The studies showed that vitamin A influenced circulating iron (hemoglobin and transferrin saturation), but no study showed that vitamin A had an effect on storage iron (indicated by ferritin concentration). Of interest is the conclusion that vitamin A had an effect over 30 <strong>Micronutrient</strong> <strong>Interactions</strong>: <strong>Impact</strong> on Child Health and Nutrition a wide range of average initial retinol concentrations (0.5–1.1 µmol/L serum). Children can be considered to have a low vitamin A status when their retinol concentration is less than 0.7 µmol/L, but vitamin A supplementation also had positive effects when concentrations were higher than 0.7 µmol/L. However, not every study reported improved iron status after vitamin A supplementation. Hemoglobin concentration of anemic lactating women with baseline retinol concentrations of 0.8-0.9 µmol/L did not increase after vitamin A (given as β-carotene) supplementation (de Pee et al. 1995). The exact mechanism of how vitamin A influences iron status still remains unclear. Vitamin A deficiency was suggested to inhibit the reuse of iron stored in liver (Bloem 1995). Studies in rats indicated that marginal vitamin A deficiency led to impaired erythropoiesis but did not impair intestinal absorption of dietary iron (Roodenburg et al. 1994). The mechanism for reuse of stored iron, however, would not explain the effect observed in the study of Suharno et al. (1993), where pregnant women had virtually no liver stores of iron and still experienced an extra effect of vitamin A. Turnham (1993) proposed that vitamin A supplementation would suppress infection and consequently stimulate the production of transferrin and retinol binding protein. However, this proposed mechanism still needs to be proven. It can be concluded that a combined supplementation with vitamin A may have a positive influence on iron status even when the vitamin A status of a population on average does not seem to be deficient. No study reported an influence of iron supplementation on vitamin A status. The positive influence of vitamin A on iron status was reported not only for supplements but also for vitamin A–fortified foods such as sugar (Mejia and Arroyave 1982) and food additives such as monosodium glutamate (Muhilal et al. 1988) consumed by children.
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