Prenatal iron supplements impair zinc absorption in pregnant Peruvian women

Prenatal iron supplements may adversely influence zinc absorption during pr egnancy. To examine the impact of prenatal iron supplements on supplemental zinc absorption, fractional zinc absorption was measured in 47 pregnant Pe ruvian women during the third trimester of pregnancy (33 +/- 1 wk gestation ). Of these 47 women, 30 received daily prenatal supplements from wk 10-24 of pregnancy until delivery. Supplements contained 60 mg of Fe and 250 mu g of folate without [iron group (Fe), n = 16] or with [iron and zinc supplem ented group (Fe + Zn), n = 14] 15 mg of Zn. The remaining 17 women [unsuppl emented control group (C)] received no prenatal supplementation. Zinc conce ntrations were measured in plasma, urine and cord blood and percentage zinc absorption was determined following dosing with oral (Zn-67) and intraveno us (Zn-70) stable zinc isotopes. Percentage zinc absorption was significant ly lower than controls in fasting women receiving iron- containing prenatal supplements (20.5 +/- 6.4 vs. 20.2 +/- 4.6 vs. 47.0 +/- 12.6%, Fe, Fe + Zn and C groups, respectively, P < 0.0001, n = 40). Plasma zinc concentration s were also significantly lower in the Fe group compared to the C group (8. 2 +/- 2.2 vs. 9.2 +/- 2.2 vs. 10.9 +/- 1.8 mu mol/L, Fe, Fe + Zn and C grou ps, respectively, P = 0.002), and cord zinc concentrations were significant ly related to maternal plasma Zn levels (y = 6.383 + 0.555x, r = 0.486, P = 0.002). The inclusion of zinc in prenatal supplements may reduce the poten tial for iron supplements to adversely influence zinc status in populations at risk for deficiency of both these nutrients.