Follow-Up Study Shows Zinc May Not Benefit Infants' Mental Development

LONDON--Prenatal supplementation with zinc alone does not seem to benefit infants' mental development, according to a follow-up study printed in the July 27 issue of The Lancet (360, 9329:290-4, 2002) (www.thelancet.com). Researchers, led by Jena D. Hamadani, M.D., from the Institute of Child Health in London, based their current study on previous results published last year that indicated infants one month of age who received 5 mg/d of zinc for five months did not score as well on mental development indexes as infants receiving placebo (Am J Clin Nutr, 74, 3:381-6, 2001).

The current study was a randomized, placebo-controlled trial set up to determine the effects of zinc supplementation during pregnancy on the mental development of the fetus. At baseline, 559 pregnant women in Bangladesh were randomly allocated to receive 31 mg/d of zinc (as zinc acetate from Dhaka-based ACME Ltd.) or placebo from four months' gestation to delivery. The effect of zinc supplementation on pregnancy outcome and on infant growth and morbidity in the first six months was assessed. Researchers then randomly selected a subsample of 168 infants from 383 who completed the six-month study. When babies in this subsample reached 13 months of age, researchers assessed mental development, rated behavior, and measured weight and height.

When researchers controlled for differences between tested and non-tested subjects, infants in the placebo group exhibited superior mental development, as well as better psychomotor development than subjects in the zinc group. Researchers concluded zinc supplementation had no significant effect on behavior or growth. They also noted that the children's nutritional status was poor, and weight-for-age at testing was strongly related to development levels, which accounted for some of the outcomes. Researchers concluded prenatal supplementation with zinc alone did not confer benefit on infants' mental development and such treatment should be considered cautiously.

"There are many factors that contribute to the mental development of children, but as this was a randomized, controlled trial, the factors should be similar in both of the groups," Hamadani said. "However, there were some differences between the groups, and these differences were controlled during the analysis. Still, the two groups were different after controlling the differences. Therefore, we can conclude that these differences are attributed to zinc supplementation."

Contrary to Hamadani's findings, research conducted by researchers at the Universidad de Chile in Santiago demonstrated zinc supplementation of 5 g/d in healthy term infants may have beneficial effects on mental development and motor quality behavior (J Pediatr, 138, 2:229-35, 2001).