Effects of calcium supplementation on calcium homeostasis and bone turnover in lactating women

Lactation is a time of calcium flux, because women secrete approximately 21 0 mg calcium/day in breast milk, and they experience a transient bone loss. The objectives of this study were to determine the effect of calcium suppl ementation on adaptive responses in calcium homeostasis during lactation an d after weaning. Two cohorts of women participated in a 6-month randomized calcium supplementation trial. Lactation cohort women (97 lactating, 99 non lactating) were studied during the first 6 months post pal-rum, and weaning cohort women (95 lactating, 92 nonlactating) were studied during the secon d 6 months post partum. Lactating women in the weaning cohort weaned approx imately 1.5 months after enrollment. PTH was 18-30% lower in lactating than in nonlactating women (P < 0.01). Serum 1,25-dihydroxyvitamin D was 11-16% higher in lactating than in nonlactating women and remained elevated for a pproximately 1.5 months after weaning (P = 0.06). Calcium supplementation d ecreased serum PTH and 1,25-dihydroxyvitamin D in lactating and nonlactatin g women similarly. At 6 months, the calciuric response to calcium supplemen tation was less in lactating (compared with nonlactating) women (P = 0.06). Biomarkers of bone turnover were higher in lactating than in nonlactating women during lactation and after weaning but were not effected by calcium s upplementation. Calcium supplementation has little effect on lactation-indu ced changes in the calcium economy.