Does adding physical activity improve spinal bone mineral density in postmenopausal women?: A cross-sectional analysis of NHANES 2011 to 2018

Physical activity (PA) is recommended for managing postmenopausal osteoporosis, yet evidence-based prescriptions for optimizing bone mineral density (BMD) remain undefined. To identify beneficial PA thresholds, this study examined the relationship between PA and total lumbar BMD in a cross-sectional analysis of 9339 postmenopausal women from the National Health and Nutrition Examination Survey 2011 to 2018. PA was quantified as Physical Activity Metabolic Equivalent of Task (PA-MET)-hours/week. The association between PA-MET-hours/week and total lumbar BMD was assessed using weighted multivariable linear regression. Nonlinear relationships were explored with smooth curve fitting and two-piecewise linear models. Subgroup analyses were stratified by age and body mass index (BMI). A significant positive association was observed between PA-MET-hours/week and total lumbar BMD (β = 0.0000, 95% CI [0.0000, 0.0001], P = .023), which was more pronounced among younger individuals (<45 years) and those with lower BMI (<25 kg/m²). The relationship exhibited a nonlinear pattern, with an inflection point at 32 metabolic equivalent of task (MET)-h/week. Subgroup analyses further identified specific beneficial thresholds, 54 MET-hours/week for younger adults (<45 years; β = 0.0004, 95% CI [0.0002, 0.0005], P < .0001) and 128 MET-hours/week for those with normal BMI (<25 kg/m²; β = 0.0003, 95% CI [0.0001, 0.0004], P < .0001). PA is positively associated with total lumbar BMD in postmenopausal women. Moderate-intensity PA of approximately 13.5 hours/week for younger individuals (corresponding to the inflection point of 54 MET-hours/week) or 32 hours/week (corresponding to the inflection point of 32 MET-hours/week) for those with normal BMI may be beneficial for lumbar spine bone health in postmenopausal women.