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Title: 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

Author
item O'BRIEN, KIMBERLY - JOHNS HOPKINS UNIVERSITY
item DONANGELO, CARMEN - UNIV FED RIO DE JANEIRO
item VARGAS ZAPATA, CARMINA - UNIV ATLANTICO, COLUMBIA
item Abrams, Steven
item SPENCER, E - CALIFORNIA PACIFIC MED CR
item KING, JANET - CHILD HSP OAKLAND RES INS

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2005
Publication Date: 2/2/2006
Citation: O'Brien, K.O., Donangelo, C.M., Vargas Zapata, C.L., Abrams, S.A., Spencer, E.M., King, J.C. 2006. 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. American Journal of Clinical Nutrition. 83(2):317-323.

Interpretive Summary: Calcium is lost from bones during lactation but recovery occurs afterwards. Most studies of this effect have been done in countries with high calcium intakes. We were interested in what changes occurred in calcium use by the body in countries where the usual calcium intake is low. Working with collaborators at Johns Hopkins University and in Brazil we evaluated calcium use by the body in pregnant and lactating Brazilian women. We found that changes occurred with higher bone loss in the early part of lactation. We also found that increasing calcium intake decreased the bone loss. These findings may be important in developing recommendations to help prevent bone loss during lactation by avoiding very low calcium intakes.

Technical 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 < 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. 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.