Background/Objective: Prostate cancer (PCa) is the most commonly diagnosed cancer among males in the United States. Compared to European American males, African American (AA) males are at increased risk for PCa and tend to have a more aggressive form of the disease. Recent laboratory studies have suggested deficiencies in vitamin D to be related with PCa risk. Serum levels of 25-hydroxyvitamin D [25(OH)D] are considered the best indicators of an individual's overall vitamin D status. However, vitamin D metabolism and physiology are modified by genetic and environmental factors such as ultraviolet radiation (UVR), skin color, diet, body mass index (BMI) and genes involved in vitamin D synthesis. The goal of this project is to study modifiers of serum 25(OH)D levels in order to improve our understanding of the role vitamin D plays on prostate cancer susceptibility in African Americans.

Methods: This case-control study consisted of AA men (N=250) accrued from a university hospital in Washington, DC. Serum levels of 25(OH)D and prostate specific antigen (PSA) levels were assessed. BMI was calculated as weight/height2 (kg/m2). Study participants completed UVR exposure and food frequency questionnaires. Skin color was measured using a reflectance meter. Logistic regression models were used to test for associations between 25(OH)D levels and PCa risk, adjusting for ancestry, age, skin pigmentation, dietary vitamin D, supplemental vitamin D, sun exposure, and other lifestyle factors. In addition, we used linear regression models to explore determinants of serum 25(OH)D levels, including dietary vitamin D intake, ancestry, skin pigmentation and UVR exposure.

Results: There were no significant baseline differences between cases and controls for serum 25(OH)D levels, dietary vitamin D and daily servings of dairy products. Baseline differences were found for age (p<.001), alcohol intake (p<.001) and supplemental vitamin D (p=.004). Multiple logistic regression analysis found no association with serum 25(OH)D levels and PCa risk. Preliminary analysis revealed that supplemental vitamin D (p=.004) and UVR exposure (p=0.03) were determinants of serum 25(OH)D level. Also, there were potential interactions between skin color, dietary vitamin D, serum 25(OH)D levels and risk for PCa.

Conclusion: Supplemental vitamin D and UVR exposure were modifiers of serum 25(OH)D levels. However, we did not observe any significant difference in serum 25(OH)D levels between AA PCa cases and controls. This is likely due to factors such as diet, skin color, BMI and UVR exposure which strongly could influence vitamin D levels and function. Understanding the role of vitamin D in PCa risk may help to explain the higher incidence of PCa among AA males.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):A78.