Recovery of BMD after pregnancy and breastfeeding-a 10-yr prospective observational study of 25-yr-old women.

Pregnancy and lactation require large amounts of calcium, potentially depleting the young-adult bone. This study investigated BMD and fluctuations of BMD resulting from parity and lactation in the PEAK-25 cohort, a prospective observational study of women all aged 25 at inclusion and 35 at follow-up. The analyses used women who were nulliparous at baseline and parous (n = 573) or nulliparous (n = 177) 10 yr later. Parity, regardless of number of pregnancies, had no negative impact; indeed, spine BMD at age 35 was higher (2.1%; p = .043). Likewise, BMD did not differ in women who breastfed, were nonlactating or nulliparous. Even the cumulative duration of breastfeeding did not make a difference. Overall, regardless of parity, in the cohort, by age 35 BMD was already decreasing, with overall losses at the FN (∆, -3.4%) and TH (∆, -2.7%), although not the spine (∆, 0.9%). Yet, BMD fluctuations associated with pregnancy, lactation, and weaning were seen in the short term. Comparing those pregnant >24 mo with those <24 mo prior to DXA, BMD was lowest in women more recently pregnant (FN, -2.2%, TH -2.7%). Women pregnant within 12 mo had 4% lower TH BMD compared with more than 36 mo (p = .054, padjusted = .032). Cumulative duration of breastfeeding was associated with bone loss, particularly beyond 15 mo (FN: ∆, -4.3%; TH: ∆, -3.7%) and lower spine BMD accretion. Despite such periods of loss, BMD recovers, evidenced by time-from-weaning to DXA. Women weaning within 6 mo of measurement had lower FN BMD than those where the interval was >24 mo (6.6% vs 1.7%; p < .001). In conclusion and despite repeated fluctuations in BMD resulting from the physiological demands of multiple pregnancies and periods of breastfeeding, BMD recovers and ultimately does not differ from that of identically aged women without children.