Spine bone mineral density increases after 6 months of exclusive lactation, even in women who keep breastfeeding.

Unlabelled: This pilot study enrolled 31 women who had breastfed exclusively for 6 months. Lumbar and thoracic BMD increased 4 and 5%, respectively. Femoral neck and total body BMD did not change. Return of menses and progestin-only pill use were two potential signals that predicted a greater increase in BMD.

Purpose/introduction: The skeleton is resorbed during lactation to provide much of the calcium content of milk. After lactation ceases, these deficits in skeletal mineral content are largely restored, such that lactation has a neutral or protective effect against the long-term risk of low bone mineral density (BMD), osteoporosis, and fragility fractures. We hypothesized that a large observational study may identify the factors that predict a greater increase in BMD after lactation ceases. A pilot study was first needed to test feasibility and the magnitude of expected BMD change.

Methods: We undertook Factors Affecting Bone formation after Breastfeeding Pilot (FABB Pilot), which enrolled women who had breastfed exclusively for 6 months and planned to wean soon. The main outcome was change in BMD between enrolment and 6 months later.

Results: Thirty-one women were recruited and completed both time points. Lumbar and thoracic spine BMD increased 4 and 5%, respectively; there was no significant change in femoral neck and total body BMD. Most women did not wean their babies as planned but continued to breastfeed multiple times per day. Despite this, a significant increase in BMD was seen in the subsequent 6 months. Return of spontaneous menses and use of a progestin-only pill at recruitment were two potential signals that predicted a greater increase in BMD during the 6 months after exclusive lactation.

Conclusions: Spine BMD increased significantly during 6 months following exclusive lactation and despite continued lactation. The factors that stimulate skeletal recovery remain to be identified.