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

Few data exist on longitudinal changes in bone calcium turnover rates across pregnancy and lactation. Our aim was to characterize calcium kinetic variables and predictors of these changes across pregnancy and early lactation in women with low calcium intakes. 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. Rates of bone calcium deposition increased significantly from EP to LP (P = 0.001) and were significantly associated with serum PTH during LP (P < or = 0.01). Rates of bone calcium resorption were also higher during LP and EL than during EP (P < or = 0.01) and were associated with both PTH (P < or = 0.01) and IGF-1 (P < or = 0.05) during LP but not during EL. Net balance in bone calcium turnover was positively associated with dietary calcium during EP (P < or = 0.01), LP (P < or = 0.01), and EL (P < or = 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. 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.