Cross-sectional study of the effects of parturition and lactation on bone mineral density later in life.

Abstract Objective: The present cross-sectional study investigated the effects of parturition and lactation on bone mineral density (BMD) later in life. Methods: The subjects were 456 premenopausal and 713 postmenopausal Japanese women aged 40–69 years old. They were classified into six subgroups at 5-year increments. Age, height, weight, menopausal status, age at menopause (in postmenopausal women), years since menopause (in postmenopausal women), parity, and total lactation period were recorded. Lumbar spine BMD (L2-4) was measured by dual-energy X-ray absorptiometry (DEXA). In each subgroup, correlations of parturition and lactation with BMD were investigated using Pearson's correlation test and multiple regression analyses. Results: In premenopausal women aged 40–44 years old ( n =143), total lactation period was inversely correlated with BMD ( r =−0.293, P P r =−0.194, P n =218), this relationship disappeared after adjusting for age, YSM, height, weight, and parity. However, in the other subgroups, there were no significant correlations between total lactation period and BMD. There were no significant correlations observed between parity and BMD in any groups. Conclusion: Reproductive history of lactation and parity does not seem to be a major determinant of BMD later in life.