The association between ultraviolet B irradiance, vitamin D status and incidence rates of type 1 diabetes in 51 regions worldwide

Aims/hypothesis This study is an analysis of the relationship between ultraviolet B (UVB) irradiance, the primary source of circulating vitamin D in humans, and age-standardised incidence rates of type I diabetes mellitus in children, according to region of the world. Methods The association of UVB irradiance adjusted for cloud cover to incidence rates of type I diabetes in children aged <14 years during 1990-1994 in 51 regions worldwide was assessed using multiple regression. Incidence data were obtained from the Diabetes Mondial Project Group. Results Incidence rates were generally higher at higher latitudes (R-2=0.25, p<0.001). According to multiple regression, UVB irradiance adjusted for cloud cover was inversely associated with incidence rates (p<0.05), while per capita health expenditure (p<0.004) was positively associated (overall R-2=0.42, p<0.0001). Conclusions/interpretation An association was found between low UVB irradiance and high incidence rates of type I childhood diabetes after controlling for per capita health expenditure. Incidence rates of type I diabetes approached zero in regions worldwide with high UVB irradiance, adding new support to the concept of a role of vitamin D in reducing the risk of the disease.