Iron and zinc supplementation improves indicators of vitamin A status of Mexican preschoolers

Background: The coexistence of multiple micronutrient deficiencies is a wid espread public health problem in many regions of the world. Interactions be tween zinc deficiency and vitamin A metabolism have been reported but no lo ngitudinal studies have evaluated the effect of iron deficiency on vitamin A. Objective: The objective of this study was to investigate the effect of sup plementation with iron, zinc, or both on vitamin A and its metabolically re lated proteins retinol binding protein (RBP) and transthyretin. Design: The study was a longitudinal, double-blind, placebo-controlled tria l in which 219 rural Mexican children aged 18-36 mo were randomly assigned to receive 20 mg Zn/d, 20 me Fe/d, 20 mg Zn/d plus 20 mg Fe/d. or placebo. Results: Six months after supplementation. plasma retinol increased in all supplemented groups. Compared with placebo, zinc supplementation was associ ated with significantly higher plasma retinol and transthyretin but the inc rease in REP was not significant. Iron supplementation significantly increa sed plasma retinol, REP, and transthyretin. Supplementation with zinc plus iron significantly increased plasma retinol but not REP or transthyretin. C hildren deficient in zinc, iron, or vitamin A (as indicated by nutrient pla sma concentration) at the beginning of the study had a significantly greate r increase in retinol than did children with adequate nutrient status. Conclusions: Supplementation with zinc, iron, or both improved indicators o f vitamin A status. The results of this study agree with previous observati ons of a metabolic interaction between zinc and vitamin A and suggest an in teraction between iron and vitamin A metabolism.