Abstract
Leisure time physical activity (LTPA) in mid-life may have beneficial effects on risk factors for hip fracture in later life. Conversely, physical activity may increase fracture risk through risk of injury, and the optimal amount of physical activity for reducing hip fracture risk remains unclear. We explored the associations between volume and intensity of LTPA in mid-life, and subsequent risk of hip fracture ascertained from linked health data. This prospective observational study used middle aged adults aged 40– 65 years from UK Biobank. LTPA volume (LTPAv) was derived from self-reported walking, moderate and vigorous activity at baseline (2006– 2010). Cox proportional hazard and Fine–Gray sub-distribution models were used to estimate the association between activity and hip fracture, which was sex-stratified. From 324,284 participants with complete data 53% were female and mean age at baseline was 54.5 (SD 7.3). Across 16 years of follow-up there were 2,674 hip fractures. In terms of LTPA volume, the lowest risk of hip fracture occurred in quintile 3 for women (HR 0.78, 95% CI 0.67–0.91), and men (HR 0.74, 95% CI 0.60– 0.90), relating to approximately one hour/day of leisure time physical activity. When activity intensities were examined separately, the lowest estimated hazards were observed for vigorous activity, at quintile 4 in women (HR 0.65, 95% CI 0.55 – 0.76) and quintile 3 in men (HR 0.64, 95% CI 0.52– 0.79), corresponding to approximately 60– 90 minutes of vigorous activity per week. In conclusion, moderately high volumes of mid-life physical activity, particularly vigorous activity, were related to lower risk of subsequent hip fracture, but these relationships appear to attenuate at higher volumes.