Occupation and risk of hip fracture.

BACKGROUND

Physical activity in old age probably protects against hip fracture. However, very little is known about the impact of occupation during working life, in terms of its physical activity level and the socio-economic status (SES) it indicates, on the risk of hip fracture in later life.

METHOD

A population-based case-control study was conducted on 416 subjects to investigate relationships between risk of hip fracture and occupational physical activity and occupation-related SES. Occupational physical activity was coded according to the proportion of the working day at ages 20 and 50 years that the subjects were likely to have spent sitting. The Australian Classification of Standard Occupations (ASCO) was used as the basis for the coding of SES, indicated by job titles.

RESULTS

Compared with those in the intermediate category, women with a sedentary job at age 50 years (odds ratio (OR) 7.2, 95 per cent confidence interval (CI) 1.2-41.9) or a mainly weight-bearing job (OR 5.1, 95 per cent CI 1.1-23.2) had an increased risk of hip fracture. A decreasing hip fracture risk with increasing SES of the longest held job was also observed.

CONCLUSION

The finding of a J-shaped relationship in women between occupational physical activity and risk of hip fracture supports the need for research into the most effective types of exercise for maintenance of bone strength. Furthermore, the protective effect of SES demonstrated in this study still need to be corroborated in other studies before establishing evidence of a causal relationship.