THE EFFECT OF CALCIUM SUPPLEMENTATION ON BONE-DENSITY DURING LACTATION AND AFTER WEANING

Background Women may lose bone during lactation because of calcium los t in breast milk. We studied whether calcium supplementation prevents bone loss during lactation or augments bone gain after weaning. Method s We conducted two randomized, placebo-controlled trials of calcium su pplementation (1 g per day) in postpartum women. In one trial (the stu dy of lactation), 97 lactating and 99 nonlactating women were enrolled a mean (+/-SD) of 16+/-2 days post partum. In the second trial (the s tudy of weaning), 95 lactating women who weaned their infants in the 2 months after enrollment and 92 nonlactating women were enrolled 5.6+/ -0.8 months post partum. The bone density of the total body, lumbar sp ine, and forearm was measured at enrollment and after three and six mo nths. Results The bone density of the lumbar spine decreased by 4.2 pe rcent in the lactating women receiving calcium and by 4.9 percent in t hose receiving placebo and increased by 2.2 and 0.4 percent, respectiv ely, in the nonlactating women (P<0.001 for the effect of lactation; P =0.01 for the effect of calcium). After weaning, the bone density of t he lumbar spine increased by 5.9 percent in the lactating women receiv ing calcium and by 4.4 percent in those receiving placebo; it increase d by 2.5 and 1.6 percent, respectively, in the nonlactating women (P<0 .001 for the effects of lactation and calcium). There was no effect of either lactation or calcium supplementation on bone density in the fo rearm, and there was no effect of calcium supplementation on the calci um concentration in breast milk. Conclusions Calcium supplementation d oes not prevent bone loss during lactation and only slightly enhances the gain in bone density after weaning. (C) 1997, Massachusetts Medica l Society.