Sedentary Behavior, Physical Activity, and Bone Health in Postmenopausal Women

Background: Post-menopausal women exhibit lower bone mineral density (BMD) and current health guidelines highlight the potential importance of reducing sedentary behavior (SB) to mitigate bone loss in this segment of the female population.

Purpose: To determine if bone health status at the femoral neck (FN) and lumbar spine (LS) can be predicted from objectively-measured SB and physical activity data in 50 community-dwelling, post-menopausal women.

Methods: Waist-mounted ActiGraph GT1M or GT3X devices were used to quantify levels of sedentary [< 100 counts per minute (cpm)], light (100-1040 cpm), and moderate- to vigorous-intensity (>1040 cpm) behavior during a consecutive, 7-day period. Daily sedentary time (DST) was operationally defined as the total amount of time each day during which SB occurred for a minimum of 10 minutes and the number of breaks in DST was designated at the total number of instances each day (based on a 1-min epoch) in which time blocks of 100 or more cpm were adjacent to time blocks containing less than 100 cpm. Accelerometry data were expressed relative to non-wear time and a minimum 4 days of at least 10 hours of daily wear time were required for accelerometer data to be considered valid for each participant. A probability estimate of meeting health-related guidelines for physical activity participation (30 min·d-1 for at least 5 d·wk-1) was also computed and bone health status (normal vs. osteopenia/osteoporosis) of FN and LS was derived from T scores generated using dual energy x-ray absorptiometry

Results: After controlling for potential confounding factors (body mass and calcium and vitamin D supplement use), binomial logistic regression analysis indicated that reduced daily sedentary time and a great number of breaks in daily sedentary time were signifi cant predictors of osteopenia/osteoporosis at the FN (Wald (1, N = 44) = 4.72, p = .030 and Wald (1, N = 44) = 4.17, p = .041, respectively, but not at the LS Wald (1, N = 44) = 0.15, p = .697 and Wald (1, N = 44) = 0.14, p = .704, respectively. Moreover, the degree of adherence to health-related PA guidelines was not a signifi cant predictor of bone health status at the FN or LS.

Conclusion: : Our findings suggest that more frequent interruptions in sedentary behavior may exert a positive impact on bone health in post-menopausal females.