Effect of lactation on postmenopausal bone mineral density of the lumbar spine

OBJECTIVE : To investigate the relationship between lactation and bone mineral density (BMD) of the lumbar spine in a cohort of 540 healthy, postmenopausal women. STUDY DESIGN : Women were selected who experienced long-term lactation (n = 155, median 18 months) or short-term lactation (n=168, median 3 months) or who were parous, nonlactating subjects (n=217). The groups were homogeneous in age and differed in body mass index, parity and age at menopause. Vertebral BMD was measured by x-ray absorptiometry. RESULTS : No statistically significant difference in BMD was found between groups or after adjusting for body mass index, number of live births and age at menopause. Even when the 86 women with the longest lactation history (median 22 months) were matched with 112 parous women with the same parity who did not lactate, we could not find any significant difference. CONCLUSION : Long-term lactation did not significantly affect postmenopausal vertebral BMD in a cohort of healthy women.