Exposure to heavy physical occupational activities during working life and bone mineral density at the hip at retirement age
Walker-Bone K., D'Angelo S., Syddall HE., Palmer KT., Cooper C., Coggon D., Dennison EM.
Background: People in sedentary occupations are at increased risk of hip fracture. Hip fracture is significantly associated with low bone mineral density (BMD) measured at the hip. Physical activity is important in the development and maintenance of BMD, but the effects of occupational physical activity on bone health are unclear. We investigated the influence of lifetime physical activity on BMD at the hip. Methods: This was a cross-sectional epidemiological study of the associations between total hip BMD measured by dual-energy X-ray absorptiometry at retirement age and lifetime exposure to occupational physical workload (standing/walking ≥4 h/day; lifting ≥25 kg; energetic work sufficient to induce sweating and manual work). Results: Complete data on occupational exposures were available for 860 adults (488 men and 372 women) who had worked ≥20 years. Their mean age was 65 years, and many reported heavy physical workplace activities over prolonged durations. There were no statistically significant associations between total hip BMD and any of these measures of lifetime occupational physical activity in men or women. Conclusions: Lifetime cumulative occupational activity was not associated with hip BMD at retirement age. Our findings suggest that, if sedentary work conveys an increased risk of hip fracture, it is unlikely that the mechanism is through reductions in BMD at the hip and may relate to other physical effects, such as falls risk. Further studies will be needed to test this hypothesis.