Ultraviolet B irradiance and incidence rates of bladder cancer in 174 countries.

BACKGROUND Although nearly half of bladder cancer cases are due to smoking, the cause of nearly half is unexplained. PURPOSE This study aims to determine whether an inverse association exists between ultraviolet B (UVB) irradiance and incidence rates of bladder cancer worldwide. METHODS This study used an ecologic approach. Age-adjusted incidence rates of bladder cancer from 2002 were obtained for all 174 countries in GLOBOCAN, a database of the International Agency for Research on Cancer. The relationship of latitude and estimated serum 25-hydroxyvitamin D [25(OH)D] with incidence rates was determined. The independent contributions to incidence rates of bladder cancer of UVB, per capita cigarette consumption in 1980, and per capita health expenditure for 2001 were assessed using multiple regression. The analyses were performed in July 2008. RESULTS Bladder cancer incidence rates were higher in countries at higher latitudes than those nearer to the equator (r=-0.66, 95% CI=-0.74, -0.57, p<0.01). Ultraviolet B irradiance was independently inversely associated with incidence rates of bladder cancer after controlling for per capita cigarette consumption (beta=-0.28, 95% CI=-0.51, -0.05; R(2) for model=0.38, p<0.0001). Further, UVB irradiance was also inversely associated with incidence rates after controlling for per capita health expenditure (beta=-0.23, 95% CI=-0.36, -0.01; R(2) for model=0.49, p<0.0001) in a separate regression model. CONCLUSIONS Further investigation is needed to confirm the associations identified in this study using observational studies of individuals. The focus of this research should include the association of serum 25(OH)D levels with risk of bladder cancer.