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

The Effect of Latitude on the Risk and Seasonal Variation in Hip Fracture in Sweden

Although the optimal requirement of vitamin D for skeletal health in the general community is controversial, vitamin D deficiency impairs bone mineralization and increases bone turnover via secondary hyperparathyroidism, thus accelerating bone loss and increasing fracture risk. Support for a role of vitamin D deficiency in the epidemiology of hip fracture is found in the seasonal variation of hip fracture incidence that is reported in several studies. If the association were causal, then the incidence and amplitude of the seasonal variation in hip fracture risk should vary by latitude. We addressed this hypothesis by examining the incidence of hip fracture in men and women aged 50 years or more from Sweden (latitudes 55 to 69°) between 1987 and 2009. In order to reduce double counting, only one fracture in a period of a year was counted per individual. Men contributed 104,888 fractures in 33,313,065 person years and women 264,362 fractures in 38,387,660 person years. The effects of season and latitude were examined by Poisson regression. As expected, hip fracture rates were higher in women than in men. After adjustment for age, season and population density, hip fracture incidence increased by 3.0% (95% CI: 2.7–3.2%) per degree increase in latitude for men and by 1.9% (95% CI: 1.8–2.1%) for women. There was a marked seasonal variation of hip fracture with the highest risk in February and lower by 37.5% in men and by 23.5% women during the summer. There were significant interactions of amplitude of the seasonal variation with latitude (p  <  0.001 for both men and women), indicating that seasonal variation during the year was more pronounced in the north of Sweden than in the south. The associations found with latitude and season is consistent with a role of vitamin D in hip fracture causation