Seasonal variations in incidence of fractures among elderly people.

OBJECTIVE To investigate seasonal variations in the incidence of fall related fractures among people 65 years and older. POPULATION AND METHODS A prospective, population based cohort study was performed on people aged 65 years and older followed up from 1990 to 1997, a total of 459,904 person years. Cases were identified through a prospective registration system. RESULTS There were 10,992 (2390 per 100,000 person years) fall related fractures. The risk was higher in the colder seasons (October through March) among people aged 65-79 years (relative risk (RR) = 1.39, 95% confidence interval (CI) 1.32 to 1.47) and in people aged 80 years and older (RR = 1.17, 95% CI 1.09 to 1.22). For arm fractures, the RR was 1.69 (95% CI 1.56 to 1.83) among people aged 65-79 years and 1.30 (95% CI 1.13 to 1.43) among those aged 80 years and older. The RR for hip fractures was 1.27 (95% CI 1.15 to 1.37) among people aged 65-79 years and 1.08 (95% CI 1.00 to 1.15) for people aged 80 years and older. Slipping on ice and snow seems to entirely explain the excessive incidence of hip and arm fractures during winter months. CONCLUSION Season affects the incidence of all types of fractures in elderly people. Slipping on ice and snow seems to be a causal mechanism behind the seasonal effect. Preventive measures targeting this causal mechanism are likely to reduce the risk of fracture, but the size of the effect is difficult to estimate with certainty.