| Summary: | Background The association of sedentary behavior and physical activity with bone mineral density (BMD) in Chinese population has been rarely studied in China, and also seldom studied in Asian populations (mainly limited in young children) by foreign countries. Considering there are great discrepancies between foreign populations and Chinese populations in genetics, dietary habits and other aspects, it is necessary to carry out relevant research in China. Objective To assess the association of sedentary behavior and physical activity with calcaneal BMD in college students, offering a reference for understanding the bone health status of college students, and for preventing osteoporosis in middle-aged and old people. Methods By use of stratified cluster sampling, 781 college students aged 19-25 years (including 518 females and 263 males) of different grades were selected from a medical university in Guangzhou from January 2021 to March 2022. Demographic and anthropometric characteristics (including sex, age, height, weight, fat mass index and fat free mass index) and lifestyle information (including daily sedentary time, time spent on physical activity in one week, frequency of dairy products, carbonated drinks and tea consumption, calcium supplement, smoking status, alcohol use status) were collected. Calcaneal BMD was measured, and compared across college students by physique and lifestyle. Multiple linear regression and binary Logistic regression were used to investigate the association of sedentary behaviors and physical activity with calcaneal BMD. Results The prevalence of normal and abnormal calcaneal BMD in all students was 50.3% and 49.7%, respectively. The prevalence of abnormal calcaneal BMD in female college students (59.4%) is higher than that in male college students (30.4%) (χ2=58.849, P<0.001). The prevalence of abnormal calcaneal BMD varied by daily sedentary time and time spent on physical activity in one week in female students (χ2=6.670, 6.559, P<0.05). After controlling for potential confounders, multiple linear regression analysis and test for trend showed that in female students, the T-score value of calcaneal BMD increased with the decrease of daily sedentary time (β=-0.17), and there was an obvious negative linear trend between them (Ptrend=0.011). And the T-score value of calcaneal BMD increased with the increase of time spent on physical activity in one week (β=0.15), and there was an obvious positive linear trend between them (Ptrend=0.004). Further analysis based on binary Logistic regression models showed that in female students, sedentary time <4 hours per day was associated with lower risk of abnormal calcaneal BMD compared with sedentary time >8 hours per day〔OR=0.17, 95%CI (0.04, 0.68), P<0.05〕, and 90-150 minutes of physical activity in one week was associated with lower risk of abnormal calcaneal BMD compared with less than 90 minutes of physical activity in one week〔OR=0.66, 95%CI (0.44, 1.00), P<0.05〕. Conclusion The prevalence of abnormal calcaneal BMD in female college students is higher than that in male college students. Both sedentary behavior and physical activity are associated with calcaneal BMD in female college students, no correlation found among male college students. Daily duration of sedentary behavior <4 hours and 90-150 minutes of physical activity in one week are associated with lower risk of abnormal calcaneal BMD. Furthermore, the shorter time spent on daily sedentary behaviors, the lower the risk of abnormal BMD.
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