Zinc nutriture of women living in a periurban Egyptian village was examined over the last 6 mo of pregnancy and the first 6 mo of lactation as one of several potential determinants of pregnancy outcome and infant development. Estimated bioavailable zinc intake was approximately 2 mg/d from diets high in phytate and fiber. Among numerous variables analyzed by multiple regression, early pregnancy weight (3 mo) and plasma zinc concentrations in the second trimester formed the best predictor model of birth weight, accounting for 39% of the variance. Bioavailable zinc intake during pregnancy was part of a profile of micronutrient intakes related to neonatal habituation behavior, a measure of early information processing. Performance on the Bayley motor test at 6 mo of age was negatively related to maternal intakes of plant zinc, phytate, and fiber, suggesting that zinc bioavailability was involved. Maternal dietary intake explained most of the variance observed in infant motor performance; however, predictive variance was amplified by the psychosocial context.
Vitamin B-6 concentrations in human milk are known to respond rapidly to changes in maternal vitamin B-6 intake. In this study, mothers were supplemented during the first 28 d of lactation with 2 or 27 mg pyridoxine (PN)-HCl/d and a subgroup of breast-fed infants of the 2-mg/d-supplemented mothers were supplemented with 0.4 mg PN-HCl/d. Vitamin B-6 intakes of breast-fed infants reflected the amount of their mother's supplement; intakes were highest for the vitamin-supplemented infants. Vitamin B-6 intake of mothers was a strong indicator of infant vitamin B-6 status. Vitamin intake of infants correlated significantly with five measures of vitamin B-6 status. Plasma pyridoxal-5'-phosphate (PLP) concentrations and birth weight were the strongest predictors of infant growth that were examined. Alkaline phosphatase activity in the mother's milk and infant plasma reflected pyridoxal-PLP ratios in these fluids, suggesting that the enzyme acts in regulating circulating vitamer concentrations.
An increasing trend towards breast-feeding infants beyond 6 mo of age has been observed in this country. The present study was designed to examine the effect of extended lactation on the concentrations of vitamins B6 and C, free and total folacin, calcium, zinc, and magnesium. Forty mothers were studied from 7 months of lactation until they stopped breast-feeding. Subjects were requested to collect milk samples monthly at a morning feeding between 7 AM and 10 AM. Between 7 and 25 mo of lactation, levels of zinc, calcium, vitamin B6, and vitamin C tended to decrease, whereas levels of free and total folacin remained unchanged. Magnesium levels decreased only after 18 mo of lactation. The decrease in concentrations of zinc and calcium paralleled the decrease in feeding frequency. Changes observed in this study on the composition of human milk may reflect physiological changes in the mammary gland during weaning.
Effects of stage of lactation, nutrient intake, and cultural differences on the composition of human milk were examined during the first 6 mo of lactation in American and Egyptian women. In both population groups zinc levels in milk decreased from 1 to 6 months of lactation. American women supplemented with Zn had higher levels of Zn in their milk than did unsupplemented American or Egyptian women. Concentrations of calcium and magnesium were not significantly different in milk of American and Egyptian women except at month 6 of lactation. Ca levels in milk of both population groups increased from 1 to 2-3 mo of lactation and then decreased at 6 mo; Mg concentrations increased from 1 to 3 mo and then reached a plateau. Similarities in the longitudinal decrease observed in Zn levels of milk in Zn supplemented and unsupplemented subjects suggested physiological regulation.
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