Zinc supplementation does not affect growth, morbidity, or motor development of US term breastfed infants at 4-10 mo of age.

Randomized, double-blind, placebo-controlled trial in healthy term breastfed infants in the United States. Forty-one infants were assigned to the zinc group, and 33 were included in the primary anthropometric analyses; the population was generally affluent, with mothers who planned to breastfeed for about 10 months.

The active intervention was 5 mg elemental zinc daily as zinc sulfate, given orally as drops each morning from ages 4 to 10 months. The zinc regimen was compared with placebo drops.

Zinc supplementation did not improve growth, gross motor development, or morbidity in these healthy term breastfed infants. In the zinc group, mean weight gain was 348 +/- 75 g/mo and mean length gain was 1.48 +/- 0.15 cm/mo, but these outcomes did not differ significantly from placebo; attained weight and length at 10 months were also not significantly different. Gross motor development on the AIMS was not significantly different between groups, and incidence or prevalence of diarrhea, otitis media, respiratory illness, fever only, and total illness also did not differ significantly. Plasma zinc was higher and plasma copper was lower at 10 months in the zinc group than in the placebo group (P < 0.05).

Primary analyses were based on a reduced active-arm sample rather than all randomized infants, and the biochemical subset was very small. The intervention period was short and the population was narrow, limiting generalizability beyond healthy, affluent, term breastfed infants. Several outcomes were reported as nonsignificant without full effect-size detail.