Variation in fracture risk by season and weather: A comprehensive analysis across age and fracture site using a National Database of Health Insurance Claims in Japan.

Although age- and season-specific effects on fracture risk have been reported, the effects of seasonality across different age groups and for different fracture sites have not yet been clarified. Therefore, our study aimed to comprehensively investigate the effects of seasonality on fracture risk across age and fracture sites using a large-scale population database of fracture incidence. Fracture data were accumulated over a 3-year period in the region of Tokyo and in surrounding areas, which accounts for a total population of 42 million. Information on fracture occurrence, fracture site, and patient demographics were obtained from the National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB). Over the study period, 508,051 fractures were identified across the following five age groups: 0-19, 20-39, 40-64, 65-79, and 80+ years. The incidence rate for fractures in 10 site groups was calculated. Fracture risk was the highest in the spring and autumn for children aged 0-19 years and was the highest in the winter for elderly individuals (65-79 and 80+ years). Toe fractures, which occurred more frequently in the summer, were the most notable exception. The risk of fracture of the distal radius and hip was associated with daily temperature and rainfall and was elevated on days with a mean temperature higher than that of the previous day. Fracture risk exhibited seasonal variations that differed between children and elderly individuals and between toe fractures and fractures at other sites. These findings can help us understand the epidemiology of fractures and develop preventive strategies, as well as aid in the allocation of healthcare resources.