Bone mineral changes during and after lactation.

To investigate variations in bone mineral density during lactation and throughout the 12 months after scheduled cessation of lactation in relation to the resumption of ovarian function. Three hundred eight mothers who decided to lactate were scheduled to fully breast-feed for 6 months, followed by a 1-month weaning period, and then suppress lactation with cabergoline. Their bone mineral density variations were compared with those of a control group of nonlactating mothers during the first 18 months postpartum. Half the lactating women were given daily oral calcium supplements of 1 g in an open design. There was a significant progressive decrease in bone mineral density in lactating women over the first 6 months, followed by recovery of bone mass up to levels that at 18 months were higher than baseline. In nonlactating women, bone mineral density increased progressively after delivery, and at 18 months postpartum had increased by 1.1-1.9% compared with baseline. Compared with lactating women who resumed menstruation within 5 months of delivery, breast-feeding mothers with longer amenorrhea initially lost more bone, but they also gained significantly more bone after resumption of menses, so there were no differences at 18 months postpartum. Oral calcium supplementation decreased bone loss, but had only a transient effect. A scheduled lactation period of 6 months, followed by a 1-month weaning period, allowed bone mineral density to reach higher values compared with early postpartum, regardless of calcium supplementation and duration of postpartum amenorrhea.