Effect of Zinc Added to Multi-Vitamin Supplementation Containing Low-Dose Vitamin a on Plasma Retinol Level in Children--a Double-Blind Randomized, Controlled Trial (Report‪)‬

INTRODUCTION Vitamin A supplementation has shown a beneficial effect on childhood mortality (1), but its effect on morbidity is not clear. Deficiency of zinc (2) and vitamin A (3) are widespread in developing-country settings, and they often co-exist. Zinc deficiency could affect the bioavailability of vitamin A and, thereby, prevent the beneficial effect of vitamin A in reducing morbidity (4). In animal models, zinc deficiency is associated with reduced retinol levels. In zinc-deficient rats, zinc supplementation, not vitamin A supplementation, increased serum retinol levels (5). Data from human studies evaluating the effect of zinc supplementation on vitamin A status are limited and are inconclusive. Some studies have reported beneficial effects of zinc on plasma vitamin A concentration (6-8), while other studies failed to confirm these findings (9,10).