Changes in bone mineral density and markers of bone remodeling during lactation and postweaning in women consuming high amounts of calcium.

A randomized clinical intervention trial to determine effects of lactation and 1 g of calcium (Ca) on bone remodeling was conducted in 15 women (calcium = 7, placebo [P] = 8) consuming 1.3-2.4 g of Ca/day from diet + prenatal supplement. Study periods were baseline, < or = 2 weeks postpartum; lactation, 3 months lactation; and postweaning, 3 months postweaning. Bone mineral density (BMD) corrected for body weight was determined by dual-energy X-ray absorptiometry (DXA). Indicators of calcium metabolism, bone turnover, and lactation were measured: calcium metabolism, parathyroid hormone (PTH), 25-hydroxyvitamin D (25[OH]D), 1,25-dihydroxyvitamin D (1,25[OH]2D); bone turnover, formation, procollagen I carboxypeptides (PICP), osteocalcin, and bone alkaline phosphatase (B-ALP), resorption, tartrate resistant acid phosphatase (TRAP); and lactation, prolactin (PRL). Mean BMD changes differed by site: baseline to lactation -4.3% (P) (p < 0.04) and -6.3% (Ca) (p < 0.01) at the lumbar spine (L2-L4) and 5.7% gains of the ultradistal (UD) radius (Ca) (p < 0.04); lactation to postweaning, -6% to -11% at all sites of the radius and ulna (Ca, P) (p < 0.04) +3% at L2-L4 (Ca) (p < 0.03); baseline to postweaning, (UD) radius -5.2% (P) (p < 0.03), UD radius + ulna -6% to -8% (Ca, P) (p < 0.04) but no significant loss of L2-L4 or total body. Bone turnover markers were higher at lactation than postweaning: PICP (+34%, p < 0.001), osteocalcin (+25%, p < 0.01), TRAP (+11%, p < 0.005) as well as PRL (+81%, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)