Associations between snowfall and hip fracture among adults aged 65 years and older in six cities in Nagano Prefecture, Japan.

Although previous studies have suggested that snowfall is a risk factor for hip fracture, most prior research has not adjusted for ambient temperature, which has also been associated with hip fracture incidence. We aimed to examine whether snowfall is associated with hip fracture incidence after adjusting for ambient temperature. We collected data on daily hospital admissions for hip fractures and meteorological variables in six cities in Nagano Prefecture, Japan, from November to March between 2014 and 2019. We employed a time-stratified case-crossover design to examine the association between snowfall and hip fracture incidence. We included a total of 2292 hip fracture cases. In models not adjusted for ambient temperature, snowfall (>0 cm versus 0 cm) 2 days before admission was associated with a significantly higher incidence of hip fracture (adjusted odds ratio: 1.16; 95% confidence interval: 1.01-1.33). Similarly, snowfall on the day before admission was associated with a significantly higher incidence of hip fracture (adjusted odds ratio: 1.15; 95% confidence interval: 1.00-1.33). However, after further adjustment for ambient temperature, the estimates attenuated toward the null, and no significant associations were observed. In contrast, we observed a significant inverse association between ambient temperature and hip fracture incidence that was independent of snowfall. Snowfall was not associated with hip fracture after accounting for ambient temperature. These findings suggest that lower ambient temperature, rather than snowfall itself, may be the primary driver of hip fracture incidence.