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BACKGROUND: Although some studies evaluated self-reported physical activity (PA) and risk of fractures, there is limited data precisely assessing the relationship between accelerometer-derived PA and the risk of fractures, and establishing the dose-response relationship between PA and fractures. This study aimed to estimate the dose-response relationship between accelerometer-measured PA and risk of fractures in middle-aged adults. METHODS: A population-based cohort study using 81,367 UK Biobank participants (median age 61.7, female: 55.5%) with a full week of accelerometer-based PA data between June 2013 and December 2015. Total PA was derived from the Axivity AX3 Accelerometer. We used the overall acceleration average (milli-gravity units, mg) of total PA as the primary exposure, and average proportion of time spent doing moderate-to-vigorous intensity activity as the alternative exposure. Participants were categorized into quantiles for each activity measure. The primary outcome was a composite of incident fractures at any site irrespective of mechanism. The secondary outcomes were incident osteoporotic fracture, hip fracture, and vertebral fracture. RESULTS: During a median follow-up period of 8.1 years, 3,748 (4.6%) participants experienced an incident composite fracture, 2,625 (3.2%) experienced an osteoporotic fracture, 587 (0.7%) experienced a hip fracture, and 324 (0.4%) experienced a vertebral fracture. Compared with participants in the first quartiles (≤22.53 mg), those in the second (>22.53-27.15mg), third (>27.15-32.56 mg) and fourth quartiles (>32.56 mg) had a lower risk of composite fracture, with adjusted hazard ratios of 0.86 (95% CI: 0.79-0.94), 0.90 (95% CI: 0.82-0.99) and 0.98 (95% CI: 0.89-1.08), respectively. There were U-shaped curves for the accelerometer-derived PA with the risk of incident composite fracture, osteoporotic fracture, hip fracture, and vertebral fracture (all P for nonlinearity < 0.001). CONCLUSION: Compared with low PA levels (less than 22.53 mg), moderate PA levels (from 22.53 mg to 32.56 mg) could considerably reduce the risk of incident fractures. However, the benefits do not increase when the PA exceeds 32.56 mg and may weaken gradually beyond this point. Therefore, it is recommended that individuals engage in a moderate level of PA.
Luo et al. (Tue,) studied this question.