Effect of zinc supplementation on the morbidity, immune function, and growth of low-birth-weight, full-term infants in northeast Brazil

In Brazil the highest incidence of low birth weight (LBW) occurs in the northeast, and diarrhea and respiratory infections are the main causes of infant mortality and morbidity. We hypothesized that LBW infants may be zinc deficient, and that this might be adversely affecting their immune function, morbidity, and postnatal growth. We therefore examined the effect of zinc supplementation on these outcomes during the first 6 mo of life. LBW full-term infants (mean birth weight 2337 g) were given daily for 8 wk either 5 mg Zn (n = 71), 1 mg Zn (n = 68) or a placebo (n = 66). Morbidity was determined prospectively through daily home visits (except on Sunday) during weeks 0-8, then twice weekly in weeks 9-26. Anthropometric measurements were made at 0, 4, 8, 17, and 26 wk. Immune function was assessed at 8 wk by the phytohemagglutinin skin test. Supplementation (5 mg Zn) was associated with a 28% reduction in diarrhea prevalence over the 6-mo period [after adjustment for confounders (P = 0.043)], and a 33% reduction in the prevalence of cough (NS, adjusted prevalence P = 0.073). All infants had a positive immune response at 8 wk. Although supplementation had no significant effect on weight and length gains from 0 to 26 wk, infants given 5 mg Zn gained more weight than infants given placebo during weeks 17-26 (P = 0.024, analysis of variance). There was no effect on any outcome with 1 mg Zn. We conclude that 5 mg Zn/d is of benefit to LBW, full-term infants who only have a modest weight deficit.