Bone calcium turnover during pregnancy and lactation in women with low calcium diets is associated with calcium intake and circulating insulin-like growth factor 1 concentrations

Abstract

Background: Few data exist on longitudinal changes in bone calcium turnover rates across pregnancy and lactation. Objective: Our aim was to characterize calcium kinetic variables and predictors of these changes across pregnancy and early lactation in women with low calcium intakes. Design: Stable calcium isotopes were administered to 10 Brazilian women during early pregnancy (EP; weeks 10-12 of gestation), late pregnancy (LP; weeks 34-36 of gestation), and early lactation (EL; 7-8 wk postpartum). Multicompartmental modeling was used to assess the rates of bone calcium turnover in relation to calcium intakes and circulating concentrations of parathyroid hormone (PTH), insulin-like growth factor 1, and 1,25-dihydroxyvitamin D. Results: Rates of bone calcium deposition increased significantly from EP to LP (P = 0.001) and were significantly associated with serum PTH during LP (P ≤ 0.01). Rates of bone calcium resorption were also higher during LP and EL than during EP (P ≤ 0.01) and were associated with both PTH (P ≤ 0.01) and IGF-1 (P ≤ 0.05) during LP but not during EL. Net balance in bone calcium turnover was positively associated with dietary calcium during EP (P ≤ 0.01), LP (P ≤ 0.01), and EL (P ≤ 0.01). The mean (±SD) calcium intake was 463 ± 182 mg/d and, in combination with insulin-like growth factor 1, explained 68-94% of the variability in net bone calcium balance during pregnancy and lactation. Conclusions: Net deficits in bone calcium balance occurred during pregnancy and lactation. Increased dietary calcium intake was associated with improved calcium balance; therefore, greater calcium intakes may minimize bone loss across pregnancy and lactation in women with habitual intakes of <500 mg calcium/d. © 2006 American Society for Nutrition.