Changes in bone mineral density and calcium metabolism in breastfeeding women: a one year follow-up study.

The aim of this study was to evaluate bone metabolism in breast-feeding women. Thirty-six healthy women (24-31 yr, mean age 28.1 +/- 1.8 yr) were divided into 2 groups: group A including 18 women that exclusively breast-fed for 6 months, and group B composed of 18 women in whom lactation was inhibited with bromocriptine. Three days and 3, 6, and 12 months after delivery, distal radius, and lumbar spine bone mineral density (BMD) and some of the main biochemical parameters of bone turnover were assessed. In group A, we detected a significant decrease (P < 0.01 vs. basal and group B) in lumbar spine and distal radium BMD during breast-feeding. An incomplete recovery of BMD was detected 6 months after breast-feeding interruption. In group B, no significant changes occurred in BMD. In group A, during lactation, serum osteocalcin and urinary hydroxyproline showed a significant increase (P < 0.01 vs. basal and group B), while parathyroid hormone was significantly decreased (P < 0.02 vs. basal and group B). No significant variations in these parameters occurred in group B throughout the study. Our findings show that a significant decrease of BMD occurs during lactation and that this decrease is only partially recovered 6 months after interrupting breast-feeding.