Ultraviolet index and racial differences in prostate cancer incidence and mortality.

BACKGROUND Studies suggest that low levels of vitamin D may be associated with prostate cancer, and darker skin reduces the body's ability to generate vitamin D from sunshine. The impact of sunshine on racial disparities in prostate cancer incidence and mortality is unknown. METHODS Using the Surveillance, Epidemiology, and End Results program database, the authors calculated age-adjusted prostate cancer incidence rates among black and white men aged ≥ 45 years by race and county between 2000 and 2009 (N = 906,381 men). Similarly, county-level prostate cancer mortality rates were calculated from the National Vital Statistics System (N = 288,874). These data were linked with the average monthly solar ultraviolet (UV) radiation index by county and data regarding health, wellness, and demographics. Multivariable regression analysis was used to assess whether increases in the UV index (in deciles) moderated the association between black race and the incidence and mortality of prostate cancer. RESULTS Compared with counties in the lowest UV index decile, prostate cancer incidence rates for white and black men were lower in counties with a higher UV index (all Ps ≤ 0.051). Incidence rates were higher for black men versus white men, but the difference by race was less for counties in the fourth to fifth UV index deciles versus those in the first decile (Ps  ≤  0.02). Mortality rates also were found to decrease with increasing UV index for white men (Ps  ≤  0.003), but increase for black men, and an unexplained increase in racial differences in mortality rates was observed with an increasing UV index. CONCLUSIONS Racial disparities in the incidence of prostate cancer were larger in some areas with less sunshine. Additional research should confirm the findings of the current study and assess whether optimizing vitamin D levels among black men can reduce disparities.