The associations of bedtime, nocturnal, and daytime sleep duration with bone mineral density in pre- and post-menopausal women

To explore the association of sleep patterns with bone mineral density (BMD) in pre- and post-menopausal women, we used a questionnaire to evaluate the sleep patterns and performed calcaneal quantitative ultrasound to estimate BMD, in 6,510 women aged 40 years or older, from June to November 2011 in Nanjing City. We found a 1.7-fold risk of osteoporosis in post-menopausalwomen with bedtime of ≥0:00 am (OR = 1.69, 95 % CI 1.39–2.13), compared to those whose bedtime of <0:00 am. post-menopausalwomen with excessive total sleep (>10 h vs. 8–9 h, OR = 1.54, 95 % CI 1.05–2.02) were shown to have a higher risk of osteoporosis, however, this high risk was not detected in those with excessive nocturnal sleep (>10 h vs. 8–9 h, OR = 0.85, 95 % CI 0.62–1.30). By contrast, post-menopausalwomen with inadequate nocturnal sleep (≤7 h vs. 8–9 h, OR = 1.68, 95 % CI 1.32–2.75), excessive daytime sleep (≥180 min vs. 0 min, OR = 1.52, 95 % CI 1.08–2.13), and noontime nap (>60 min vs. 0 min: OR = 1.37, 95 % CI 1.06–1.76) were demonstrated to have higher risk of bone loss. Nevertheless, these associations were not found in premenopausal women. We conclude that delayed bedtime, nocturnal sleep deprivation, excessive daytime sleep, and noontime nap, but not reduced total sleep duration, could promote bone loss in post-menopausalwomen, which might be related to circadian rhythm disturbances. However, they have limited influences to BMD in women who were still in menstruating. Mechanism responsible for the phenomena warrants further investigation.