Effects of age at first pregnancy and breast-feeding on the development of postmenopausal osteoporosis

Objective: Although pregnancy and breast-feeding require adequate calcium mobilization, it is not known if these affect the acquisition of a healthy peak bone mass (PBM) and, hence, postmenopausal osteoporosis (OPS). The objective of this study was to analyze previous pregnancies and/or breast-feeding and their association with OPS. Methods: After obtaining institutional review board approval, postmenopausal women (>49 y) presenting for a dual-energy x-ray absorptiometry bone density scan were invited to participate. Risk factors for OPS, including previous fractures, pregnancy information, and dual-energy x-ray absorptiometry results, were collected. OPS was defined as a T score of -2.5 or lower. Results: Data were obtained from 619 women. Of these, 49.8% were smokers, 27.2% used a bisphosphonate, 64.1% used hormone therapy, and 5.5% had used steroids. Based on PBM, ages at first pregnancy were dichotomized to younger than 27 years and 27 years or older. Women with a history of breast-feeding had a lower prevalence of OPS (7.6%) versus women who had never breast-fed (18.7%; P < 0.001). Women with a first pregnancy when they were 27 years or older and a history of breast-feeding had the lowest prevalence of OPS (4.6%) versus women with a first pregnancy when they were younger than 27 years and no history of breast-feeding (16.3%; P = 0.001). Conclusions: Breast-feeding seems to significantly decrease the incidence of postmenopausal OPS. Women whose first pregnancy occurs after PBM (>= 27 y of age) and who have a history of breast-feeding had the lowest prevalence of OPS. Thus, an association between OPS and both breast-feeding and age of pregnancy seems to be present.