Zinc supplementation during pregnancy and effects on mental development and behaviour of infants: a follow-up study

Zinc deficiency is widely prevalent in developing countries. Zinc supplements given to Bangladeshi pregnant women have been shown to reduce infants' infectious disease morbidity. We assessed these infants at age 13 months to establish the effect of antenatal zinc supplementation on infant development and behaviour.

The study originally consisted of 559 pregnant women who were randomly allocated to zinc (30 mg daily) or placebo (cellulose) from 4 months' gestation to delivery. The effect of zinc supplementation on pregnancy outcome and on infant growth and morbidity in the first 6 months was assessed. We then randomly selected a subsample of 168 infants from 383 who completed the study at 6 months. When babies in this subsample reached age 13 months, we assessed mental development with Bayley scales of infant development-II, rated behaviour on a modified version of Wolke's scales, and measured weight and height.

When we controlled for differences between tested and non-tested participants, infants in the placebo group had higher scores on mental development index (regression coefficient=3.3, SE 1.6, 95% CI 0.2-6.5, p=0.04) and psychomotor development index (5.1, 2.4, 0.2-9.9, p=0.04) than those in the zinc-supplemented group. Zinc supplementation had no significant effect on behaviour or growth. The children's nutritional status was poor, and weight-for-age at testing was strongly related to developmental levels, which accounted for some of the treatment effect.

Prenatal supplementation with zinc alone in poor women from Bangladesh does not seem to confer benefit on infants' mental development. Such treatment should be considered with caution.