Observational studies have been used to examine children with and without zinc-deficient diets. Although observational studies can yield useful information about zinc deficiency, findings may be confounded by poverty and other nutritional deficiencies because they often co-occur with zinc deficiency and are associated with children’s development (25
). Randomized trials are necessary to examine the specificity of zinc deficiency on children’s behavior and development. Several reviews have examined the relationship between zinc nutriture and children’s behavior and development (1
Although zinc supplementation during pregnancy has been associated with several indicators of reproductive success including fetal growth, birth weight, lack of congenital malformations and term delivery, results have been difficult to replicate, which has produced inconsistent findings (26
). One trial of zinc supplementation during pregnancy examined fetal heart rate and activity. Pregnant women who received 15 mg of daily zinc, along with iron and folate supplementation, had fetuses with an increased fetal heart rate and more vigorous fetal activity compared to fetuses of nonsupplemented women (30
). Both measures are indices of fetal well-being that may be related to subsequent development (31
Observational studies in Egypt reported an association between mothers’ diets and their infants’ early behavior and development (32
). Mothers who consumed diets high in animal products had infants who were more attentive shortly after birth, as measured on the Brazelton Neonatal Behavioral Assessment Scale, than infants of mothers who consumed diets low in animal products. At 6 mo, infants whose mothers consumed diets that were primarily plant based, and therefore low in bioavailable zinc, had lower motor scores on the Bayley Scales of Infant Development than infants whose mothers consumed animal-based diets. Motor development was also related to infant diarrhea and psychosocial factors such as household socioeconomic status. These findings demonstrate the multiple impacts of maternal dietary choices and psychosocial risk on children’s early motor functioning.
There are at least six zinc-supplementation trials that have examined the effects of zinc supplementation on activity or development among infants. In India, low-income toddlers who received 10 mg of elemental zinc daily for 6 mo had more vigorous activity during play, compared with control toddlers (34
). In Guatemala, stunted toddlers who received 10 mg of oral zinc daily for 7 mo had more functional activity during play, compared with control toddlers (35
). However, the toddlers did not differ on an observational assessment of motor development. A supplementation trial among very low-birth–weight infants (< 1500 g) from Canada (36
) showed that infants who received formula with a higher concentration of zinc (11 vs 6.7 mg/L) for the first 5 mo of life had better scores in motor development, measured on the Griffiths’ Developmental Assessment, but not in other areas of development. In Brazil, low-birth–weight infants who received 5 mg of zinc for 8 wk were more cooperative during developmental testing but there were no differences in their mental or motor development when measured on the Griffiths’ Assessment (37
). In Chile, low-income infants who received 5 mg of elemental zinc daily for 1 y had higher scores in motor quality (gross and fine-motor movement and control), but there were no differences in the children’s mental or motor scores on the Bayley Scales (38
). In Bangladesh, low-income infants received 5 mg of elemental zinc daily from 4 wk to 6 mo of life (39
). When the evaluations were conducted by administering the Bayley Scales at 7 and 12 mo, there were no differences in motor development at either evaluation time; but at the 12-mo assessment the zinc-supplemented infants had slightly lower cognitive scores compared with control infants (103.1 vs 106.4). Thus, the evidence linking zinc supplementation to early cognitive and motor development is inconclusive. There are suggestions that zinc supplementation may promote activity and perhaps motor development in the most vulnerable infants. Although motor development is thought to promote cognitive development by enabling children to be more independent and to explore their surroundings (40
), the only evidence linking zinc supplementation to cognitive development is counter intuitive.