title: Effects of calcium supplementation and lactation on iron status.
abstract: Calcium has been shown to inhibit iron absorption. The consequences of chronic calcium supplementation on iron status are unclear, however. As part of a randomized calcium-supplementation trial in lactating and nonlactating women in the postpartum period, we determined whether long-term calcium supplementation and lactation status affected iron stores as measured by serum ferritin concentrations. Subjects (95 lactating and 92 nonlactating) were enrolled at approximately 6 mo postpartum and then randomly assigned to receive either 500 mg Ca as calcium carbonate or a placebo twice daily with meals for 6 mo. Lactating women weaned their infants approximately 2 mo after enrollment (ie, approximately 8 mo postpartum). Calcium supplementation had no effect on serum ferritin concentrations. At the end of the study, geometric mean serum ferritin concentrations were 28.4 microg/L in the calcium-supplemented group and 27.5 microg/L in the placebo group (P > 0.5). Lactation status was significantly related to serum ferritin concentrations. At baseline, serum ferritin concentrations were higher in lactating women than in nonlactating women (47.7 compared with 31.5 microg/L, P < 0.001). In lactating women, serum ferritin concentrations decreased by a mean of 17 microg/L after weaning. By 12 mo postpartum, mean serum ferritin concentrations in women who were previously lactating were not significantly higher than those of nonlactating women (30.5 compared with 25.5 microg/L). These findings provide reassurance that long-term calcium supplementation does not impair iron stores. Furthermore, lactation status should be considered when assessing iron nutriture of women and determinants of iron status in populations.
authors.affiliation: Department of Pediatrics, Children's Hospital Medical Center, Cincinnati, OH 45229, USA. heidi.kalkwarf@chmcc.org
authors.forename: H J
authors.initials: HJ
authors.lastname: Kalkwarf
authors.forename: S D
authors.initials: SD
authors.lastname: Harrast
mesh_terms: D000328:Adult; D002136:Calcium, Dietary / Q000008:administration & dosage / Q000494:pharmacology*; D019587:Dietary Supplements; D005260:Female; D005293:Ferritins / Q000097:blood; D006801:Humans; D007501:Iron / Q000008:administration & dosage / Q000378:metabolism*; D007774:Lactation / Q000378:metabolism*; D009752:Nutritional Status; D049590:Postpartum Period
chemical_list: D002136:Calcium, Dietary; D005293:Ferritins; D007501:Iron