Children born to women living in areas where zinc deficiency is common frequently suffer from poor health and developmental delays, but those whose mothers take zinc supplements while pregnant have sharply reduced risks of some illnesses during infancy, according to findings from a randomized trial in urban Bangladesh.1 Through age six months, infants whose mothers took zinc supplements during the last two tri-mesters of pregnancy had significantly lower risks of acute diarrhea, dysentery and impetigo than those whose mothers took placebo tablets. When the sample was divided by size at birth, these effects were seen only in low-birth-weight babies, who typically have high rates of illness and death.
Women living in Dhaka were enrolled in the study at 12-16 weeks' gestation and were randomly assigned to take either daily zinc supplements (30 mg) or a placebo throughout the remainder of their pregnancy; they saw a health care worker each week to receive a fresh supply of tablets. Fieldworkers conducted weekly follow-up visits in the women's homes for up to six months after the birth. During these visits, they asked the women detailed questions about the infants' health, to assess the occurrence of respiratory infections, diarrhea, fever, skin diseases and other illnesses; doctors examined infants who required medical attention. All babies were weighed and measured at monthly visits; blood was taken to measure infants' serum zinc levels at one month and six months of age.
A total of 420 infants were included in the analyses--199 whose mothers had taken zinc supplements and 221 whose mothers had taken placebo tablets. The two groups of mothers were of similarly young age and low socioeconomic status. All infants were breastfed throughout the study, but few were exclusively breastfed for the entire period. Between birth and six months, the infants' growth rates and serum zinc concentrations were similar, regardless of whether their mothers took zinc supplements or placebo.
The researchers used regression techniques to compare the frequency of disease in the two groups of infants, controlling for the mothers' socioeconomic status, parity and serum zinc level at the beginning of the study. Infants whose mothers had taken zinc had significantly lower risks of acute diarrhea (risk ratio, 0.8), dysentery (0.4) and impetigo (0.5) than did those in the placebo group; they also were ill with dysentery or impetigo for significantly fewer days. Zinc supplementation had no association with the frequency of persistent diarrhea, cough or acute lower respiratory infection.
When the analysts looked separately at the data for infants who had been underweight (i.e., less than 2,500 g) at birth and those who had been of normal weight, they found that the effects of zinc supplementation were limited to infants of low birth weight. Among these infants, the risks of acute diarrhea, dysentery and impetigo were reduced by 32-74% if the mother had taken zinc supplements during pregnancy. The association between zinc supplementation and number of days ill with dysentery or impetigo also was significant only for low-birth-weight babies.
The researchers conducted separate analyses using data on low-birth-weight infants born at term and those who were preterm. For full-term low-birth-weight infants, the risks of acute diarrhea, all diarrheal episodes and impetigo were significantly reduced (risk ratios, 0.3-0.6) among those whose mothers had used zinc supplements. No association was found between zinc supplementation and disease among preterm low-birth-weight infants.
Summing up their findings, the researchers note that while babies born to women who take zinc supplements may be small at birth, they "might have a less compromised immune system" than those whose mothers do not take zinc. Therefore, the investigators suggest that low birth weight is "mainly an indicator of risk rather than [a] direct cause of morbidity and mortality," and recommend that future studies assess not only the frequency but the consequences of low birth weight. They conclude that given the apparent contribution of maternal zinc supplementation to reductions in poor health outcomes among low-birth-weight infants, "consideration should be given to the addition of zinc to regular antenatal supplements" in regions where low birth weight is common.--D. Hollander
1. Osendarp SJM et al., Zinc supplementation during pregnancy and effects on growth and morbidity in low birthweight infants: a randomised placebo controlled trial, Lancet, 2001, 357(9262):1080-1085.