Factors underlying changes in bone mineral during postpartum amenorrhea and lactation

To determine the physiologic and habitual factors that may modulate changes in bone mineral density (BMD) postpartum, dual-energy X-ray absorptiometry was performed at the lumbar spine, right femoral neck and dominant distal radius immediately after delivery, after resumption of menses, and 1 year thereafter in a cohort of 41 healthy postpartum Finnish women aged 31.5 (SD 4.6) years. Mean durations of lactation and postpartum amenorrhea (PPA) were 7.7 (3.7) and 5.9 (2.9) months, respectively. After PPA, significant bone losses of 2%-4% were observed at the lumbar spine and femoral neck. Duration of PPA and different lactational variables explained (adjusted R2) from 21% to 27% of the variability in changes in BMD during PPA. A recovery to postpregnancy BMD levels was observed at the lumbar spine; in contrast BMD at the femoral neck showed only a partial recovery. The duration of unsupplemented lactation was weakly (adjusted R2 = 0.13) associated with recovery at the lumbar spine, while a long duration of total lactation also showed a weak association (adjusted R2 = 0.02) with delayed recovery at the femoral neck. In conclusion, a systematic bone loss occurs during PPA, and after resumption of menstruation BMD recovers despite continued lactation. However, the time of bony recovery back to postpregnancy level seems to be modulated slightly by lactation habits. It is obvious that the control of postpartum BMD changes is a multifactorial process that may be specific to the skeletal site of interest.