Vitamin D status may explain racial disparities in survival among patients with advanced renal cell carcinoma in the targeted therapy era

In a recent article, Rose et al reported significantly reduced overall survival (by approximately 10%) for African Americans versus white Americans among patients with advanced renal cell carcinoma (RCC) in both the pre–targeted therapy era and the post–targeted therapy era. Both treatment and socioeconomic status were ruled out as explanations. Another recent article reported a significantly increased risk of death among RCC patients for African Americans versus white Americans in models adjusted for tumor characteristics and comorbid conditions, but this increase did not remain after further adjustments for the education level and deprivation index. A factor not considered in either article is the role of ultraviolet B (UVB) exposure and the vitamin D status. There is strong evidence from ecological and observational studies showing that UVB doses and serum 25hydroxyvitamin D (25(OH)D) concentrations are inversely correlated with the incidence and/or mortality rates of many types of cancer, including RCC. The ecological study results were first reported in Cancer and are summarized in a review. The ecological study findings for RCC are weaker than those for a number of other types of cancer, however. Occupational UVB exposure has also been found to be inversely correlated with the incidence of RCC. There are also several observational studies reporting inverse correlations between 25(OH)D concentrations and the risk for RCC. African Americans have mean 25(OH)D concentrations approximately 40% lower than those of white Americans. There are many diseases, including autoimmune diseases, many types of cancer, cardiovascular disease, diabetes mellitus, infectious diseases, mental illnesses, and neurocognitive dysfunction, linked to low UVB exposure and 25(OH)D concentrations. A review published in 2010 outlined the evidence showing that the vitamin D status accounted for some black-white health disparities. Subsequently, evidence was summarized for the role of the vitamin D status in black-white cancer-specific and overall survival disparities. In this study, the mortality rates for African Americans were on average approximately 25% higher than those for white Americans after consideration of the stage at diagnosis and treatment. The 25% value was consistent with the understanding of the 25(OH)D concentration–cancer incidence relation, which was recently updated on the basis of case-control studies of breast cancer incidence rates. There is additional evidence for the beneficial effects of vitamin D on overall mortality rates. A meta-analysis of 32 studies found a strong inverse correlation between the all-cause mortality rate and the 25(OH)D concentration for 25(OH)D concentrations< 36 ng/mL, with no further changes at higher concentrations. A meta-analysis of 14 vitamin D3 clinical trials found a relative risk of death of 0.89 (95% confidence interval, 0.80-0.99). For 8 trials using vitamin D, the relative risk of death was 1.04 (95% confidence interval, 0.97-1.11). A recent review presented an overview of the evidence showing that UVB exposure and vitamin D reduce the incidence of many types of cancer and increase survival. Primarily on the basis of observational studies, 25(OH)D concentrations should be raised to 30 to 40 ng/ mL for optimal health.