The relationship between joint pain and climate conditions in Japan.

This study aimed to determine whether there was any association between the regional climate and the proportion of people with joint pain. Regional climate data between 1971 and 2000 were obtained from the Japan Meteorological Agency. The variables used in the cluster analysis included sunlight hours, amount of precipitation, number of days with precipitation, and temperature. The regional proportion of people with joint pain was obtained from the National Survey for Health in 2001. After performing a cluster analysis, one-way ANOVA and Welch's test were used to determine whether the climate characteristics of the clusters were significantly different. Within each cluster, stepwise multiple linear regression analyses were performed. We found that sunlight hours showed a direct, negative association with the proportion of people with joint pain (adjusted R2=0.532, p=0.016) in cluster 1, which was characterized as the region with the fewest total hours of sunlight, less precipitation, a modest number of rainy days, and low temperature. In the other clusters, the regional female population rate (cluster 2) and the senior population rate (cluster 3, 4) were the primary predictors. We concluded that the degree of exposure to sunlight may play a crucial role in prevention of joint pain. This finding should encourage people to set aside some time for staying outdoors in their daily lives.