Association between latitude, temperature, sunshine hours, and sunshine rate and the incidence of type 1 diabetes in Hokkaido, Japan: an ecological study

Abstract Objective This study aimed to examine the relationships between latitude, temperature, sunshine hours, and sunshine rate and the incidence of type 1 diabetes (T1D) in Hokkaido, Japan. Results We analysed data from the Childhood IDDM Hokkaido Registry, including 458 paediatric T1D cases diagnosed before age 15 between 1959 and 1996. Regional incidence rates were calculated using census data, and meteorological variables were obtained from the Japan Meteorological Agency. Linear regression models examined correlations between T1D incidence and latitude, mean temperature, sunshine hours, and sunshine rate. T1D incidence exhibited regional variation, with the highest rate in Ishikari (1.32 per 100,000 person-years) and the lowest in Hiyama/Oshima (0.53 per 100,000 person-years). A positive association was observed between latitude and T1D incidence. Additionally, mean temperature correlated positively with incidence, suggesting a complex interplay between climatic factors. Lower annual sunshine hours and reduced sunshine rates were associated with increased T1D incidence, supporting the hypothesis that diminished sun exposure contributes to disease risk. Higher latitude and reduced sunshine exposure were associated with increased T1D incidence, highlighting the potential influence of sunlight availability and vitamin D status. Promoting adequate vitamin D levels and safe sun exposure may help mitigate T1D risk in high-latitude populations.