Zinc homeostasis during lactation in a population with a low zinc intake

Abstract

Background: There is a major increase in endogenous zinc excretion, specifically via the mammary gland, in early human lactation. Whereas fractional absorption of dietary zinc has been reported to increase in early human lactation, it is not known to what extent adaptive mechanisms may maintain zinc homeostasis, especially when dietary zinc intake is relatively low. Objective: The objective of this study was to quantitate major variables of zinc homeostasis during early lactation in subjects from a population whose habitual dietary zinc intake is low. Design: We studied 18 free-living lactating women from a rural community of northeast China whose infants were exclusively breast-fed. The subjects were studied at ≈ 2 mo of lactation with use of stable isotopes of zinc and metabolic collection techniques. Milk volume was measured with use of a deuterium enrichment method. Results: The mean (±SD) secretion of zinc in milk was 2.01 ± 0.97 mg/d, the intake of zinc was 7.64 ± 1.61 mg/d, and the fractional absorption of zinc was 0.53 ± 0.09, for a total daily zinc absorption of 4.00 ± 0.71 mg/d. Endogenous zinc excretion in urine and feces was 0.30 ± 0.10 and 1.66 ± 0.97 mg/d, respectively. Conclusions: Zinc balance, including zinc secreted in breast milk, was maintained at ≈ 2 mo of lactation in women whose habitual diet was low in zinc. Homeostasis was achieved by high fractional absorption of zinc and intestinal conservation of endogenous fecal zinc.