ZINC, CALCIUM AND MAGNESIUM IN HUMAN LACTATION: A COMPARISON OF MINERAL LEVELS IN MILK OF AMERICAN AND EGYPTIAN WOMEN AND GROWTH OF THEIR INFANTS

MIHIRA VEDULA KARRA, Purdue University

Abstract

Egypt is an area where human deficiencies of minerals, zinc in particular, have been observed. This prompted an examination of the adequacy of mineral levels, i.e. zinc, calcium and magnesium in milk of Egyptian women for their infants as contrasted to well-nourished American counterparts. Effects of cross-cultural differences in diet and infant feeding practices, stage of lactation, time of day and supplement intake on mineral composition of breast milk were examined. Mineral levels were similar in milk from American and Egyptian women; zinc levels decreased from 1 to 6 months of lactation while calcium levels increased from 1 to 3 months and then declined. Magnesium concentration of breast milk increased during the early months and then plateaued. Long-term supplementation of American mothers with 25 mg zinc daily from 1 to 6 months of lactation was associated with increased zinc levels in plasma and milk. Short-term oral supplementation of American mothers, at 7-9 months postpartum, with 50 mg zinc daily for a 30 day period, mitigated the rate of decline in the level of zinc in milk when compared to unsupplemented American women. Identical short-term supplementation of Egyptian women did not affect the zinc concentration of their milk. This possibly reflected poor zinc absorption due to the high levels of fiber and phytates in their diets. Variation in maternal intake of calcium and magnesium did not affect levels of these minerals in breast milk. Zinc and magnesium levels in milk of American women exhibited significant diurnal variations with highest concentrations in milk collected in the morning and lowest levels in milk collected in the afternoon. Concentration of all three minerals in milk decreased from the beginning to end of a feeding. Although Egyptian infants weighed less than American infants at all ages, growth rates of all infants were within normal standards. Normal growth concomitant with mineral intakes below the RDA support the conclusion that current RDA's for zinc, calcium and magnesium for infants are set at unnecessarily high levels.

Degree

Ph.D.

Subject Area

Nutrition

COinS