Randomized controlled trial of the effect of zinc supplementation on the mental development of Bangladeshi infants

Background: Zinc deficiency is thought to be common in young children in developing countries and some data suggest that it may detrimentally affect children's development. Objective: Our goal was to assess the effect of zinc supplementation on the developmental levels and behavior of Bangladeshi infants. Design: This was a randomized, double-blind, controlled trial conducted in Dhaka, Bangladesh. Three hundred one infants aged 1 mo were randomly assigned to receive either 5 mg elemental Zn or placebo daily for 5 mo, and subsequent growth and morbidity were observed. For the present study, developmental levels were assessed in a subsample of 212 infants at 7 and 13 mo of age with use of the Bayley Scales of Infant Development, and the infants' behavior during the tests was observed. The children's social backgrounds, weights, and lengths were also recorded. Results: The children's nutritional status was generally poor. The zinc-treated group had slightly lower scores on the mental development index of the Bayley Scales than did the placebo group (β = 3.7, SE = 1.3, P < 0.005). This effect remained significant when nutritional status and social background were controlled for. No other significant differences between groups were noted. Conclusions: The mental development index scores of the zinc-treated group were slightly but significantly lower than those of the placebo group. This finding may have been due to micronutrient imbalance. Caution should be exercised when supplementing undernourished infants with a single micronutrient.