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

Background: It has been documented that growth patterns differ between breastfed and formula-fed infants. Some investigators have suggested that these differences may be related to differences in zinc nutriture. Objective: The objective of this study was to examine the effect of zinc supplementation on growth, morbidity, and motor development in healthy, term, breastfed infants. Design: We conducted a randomized double-blind intervention comparing zinc supplementation (5 mg/d as zinc sulfate) with placebo in breastfed infants aged 4-10 mo. Growth and indexes of body composition and gross motor development were measured monthly from 3 to 10 mo. Morbidity data were collected weekly. Results: Eighty-five infants were enrolled, and 70 completed the study. The baseline characteristics, attained weight or length at 10 mo, growth velocity, gross motor development, and morbidity did not differ significantly between groups, even after control for potentially confounding variables. Conclusions: The dietary zinc intake of these breastfed infants appeared to be adequate, given that zinc supplementation did not affect growth, development, or risk of infection (although sample size for detection of differences in development or infection was limited). Previously described differences in growth between breastfed and formula-fed infants in such populations do not appear to be due to differences in zinc nutriture.