Bone metabolism after human parturition and the effect of lactation: longitudinal analysis of serum bone-related proteins and bone mineral content of the lumbar spine.

A prospective study was performed to investigate postpartum changes in human bone metabolism and the effects of lactation on them. The subjects consisted of two groups: 13 women who stopped breast-feeding within 3 months postpartum (short-term group) and 14 women who continued breast-feeding for more than 6 months postpartum (long-term group). Serum carboxyl-terminal propeptide of type I procollagen (PICP), carboxyl terminal cross-linked telopeptide of type I collagen (ICTP), and bone gla protein (BGP) were measured prepartum, and at 5 days, 1 month, 3 months and 9 months postpartum. Lumbar BMD was measured at 3-7 days, 3 months and 9 months postpartum. Between prepartum and 3 months postpartum, the values and variations in the markers were essentially the same in both groups. PICP was maintained at a constant and significantly higher level than the control value. In contrast, ICTP had increased markedly at 5 days postpartum, gradually decreasing thereafter. BGP was low prepartum and gradually increased. At 9 months postpartum, PICP and ICTP decreased to the control values in the short-term group. The postpartum time course of lumbar BMD showed a significant decrease in both groups at 3 months postpartum. Recovery to the puerperal level was seen at 9 months postpartum in the short-term group but not in the long-term group. In conclusion, bone resorption is stimulated by parturition as well as lactation resulting in postpartum loss of lumbar BMD.