ArticlesZinc supplementation during pregnancy and effects on mental development and behaviour of infants: a follow-up study
Introduction
Zinc deficiency is widely prevalent in the developing world, where diets contain low levels of animal protein and high fibre and phytate. Zinc supplementation improves growth1 and reduces morbidity2 in zinc-deficient children, and there is some evidence that it improves children's development, but findings are inconsistent.3 Pregnant women are also thought to be at high risk of zinc deficiency because of an increased physiological requirement.4 Some investigators have noted that maternal zinc intake or plasma zinc concentration is positively related to pregnancy outcome, whereas others have failed to show an association.5, 6 Trials during pregnancy have had inconsistent findings about the effects of zinc supplementation on birthweight and length of gestation.7
Does zinc deficiency in pregnancy adversely affect the mental development of offspring? Results of studies in animals have shown that severe zinc deficiency during pregnancy affects brain development8 and behaviour of offspring.9 In an observational study of pregnant women in Egypt, maternal intake of fibre and phytate, which are inhibitors of zinc absorption, was negatively related to infants' motor development.10 Furthermore, maternal intake of foods from animal sources was a significant predictor of the newborn baby's speed of encoding information.11 The investigators suggested that zinc bioavailability might play a part in this relation. Fetal neurobehavioural development improves when zinc is added to iron and folate supplement during pregnancy.12 However, we are unaware of any trial to assess the effect of zinc supplementation in pregnancy on subsequent mental and motor development of offspring.
In 1997, pregnant Bangladeshi women took part in a randomised controlled trial to examine the effect of zinc supplementation from the fourth month of pregnancy to term, on the outcome of pregnancy13 and subsequent growth and morbidity of the infants in the first 6 months of life.14 There was no benefit with regard to birthweight or gestational age at birth, but low birthweight infants whose mothers received zinc supplements had a reduced rate of infections. We took the opportunity presented in that study to examine the effect of prenatal zinc supplementation on development. We postulated that zinc supplementation of pregnant women would benefit the psychomotor and mental development and behaviour of their offspring.
Section snippets
Methods
The study was done in slum areas of Dhaka, which are characterised by high population density, poor housing, multifamily latrines and water sources, poor sewerage and drainage facilities, and irregular rubbish collection. The study was approved by the research and ethical review committees of International Centre for Diarrhocal Disease Research, Bangladesh (ICDDR, B). Prior informed consent was obtained from the parents of the children.
Results
The figure shows the trial profile. Of 240 randomly selected infants, four had died before our study began, one had epilepsy and was excluded, five refused to come for further assessment, and eight were ill and by the time they recovered had exceeded the age required by the selection criteria for testing. Another 54 infants could not be found. We therefore located a total of 168 children from our subset of 240 (zinc=83, placebo=85).
We compared the characteristics at enrolment of the mothers of
Discussion
We have shown that zinc supplementation of pregnant women was associated with lower Bayley scores in their infants than in the placebo group. The difference remained significant when we controlled for differences between tested and non-tested participants, and between treatment groups. The deficit was small, about a third of 1 SD. Children of zinc-treated mothers were also less cooperative during the test and fussier than the placebo group, but this difference disappeared when we controlled for
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