Sex-stratified associations between movement behaviors and QUS-defined osteoporosis in rural adults: an isotemporal substitution analysis

Background Previous studies have explored the independent effects of different movement behaviors on osteoporosis (OP), but limited research on their substitution effects, especially among rural adults in resource-limited areas. This study investigates the associations between hypothetical time reallocations among different movement behaviors and QUS-defined osteoporosis. Methods This cross-sectional study included 7368 participants selected from the second wave survey of the Henan Rural Cohort Study. Osteoporosis was defined using calcaneal quantitative ultrasound (QUS), and participants with a QUS T-score ≤ − 2.5 were classified as having QUS-defined osteoporosis. Logistic regression and restricted cubic spline were applied to examine the relationships between movement behaviors and QUS-defined osteoporosis. The isotemporal substitution model was employed to evaluate associations under hypothetical time reallocations among behaviors. Results Long nocturnal sleep duration was associated with higher odds of QUS-defined osteoporosis in both sexes, while daytime napping was associated with higher odds in women. Sedentary behavior was associated with higher odds in men ( OR : 1.58, 95% CI : 1.05–2.37), whereas walking was associated with lower odds in both sexes (all P < 0.05). Isotemporal substitution analysis showed that reallocating 30–60 min from nocturnal sleep, sedentary behavior, or moderate-to-vigorous physical activity (MVPA) to walking was associated with lower odds of QUS-defined osteoporosis in both sexes (all P < 0.05). In women, reallocating 30 min of daytime napping to walking was also associated with lower odds of QUS-defined osteoporosis ( OR : 0.90, 95% CI : 0.85–0.95). In addition, reallocating 30 min of nocturnal sleep to MVPA was associated with lower odds of QUS-defined osteoporosis in women ( OR : 0.97, 95% CI : 0.94–0.99). Conclusion In this cross-sectional study, hypothetical reallocation of 30–60 min from nocturnal sleep, sedentary behavior, or MVPA to walking was associated with lower odds of QUS-defined osteoporosis. In women, reallocating the same duration from nocturnal time to MVPA was also associated with lower odds. Clinical trial registration The Henan Rural Cohort Study has been registered at Chinese Clinical Trial Register (Registration number: ChiCTR-OOC-15006699). Date of registration: 2015-07-06. http://www.chictr.org.cn/showproj.aspx?proj=11375 .