Diet and prostate cancer: Investigating the relationship between risk of prostate cancer and serum concentrations of individual carotenoids, selenium, and alpha-tocopherol in United States Black and White men

The public health importance of prostate cancer is well recognized. It is the most commonly diagnosed cancer, and the second leading cause of cancer mortality, among men living in the United States (US). For unknown reasons, African-American men bear a disproportionately heavy burden from this disease, with incidence rates over 50% higher than those for US Whites. A clear explanation for this racial difference has not been offered. The etiology of prostate cancer likewise remains mysterious. The three manuscripts encompassed in this dissertation address these issues by examining several dietary hypotheses for prostate cancer among US Black and White men. The investigations used serologic data from a National Cancer Institute multi-center, population-based case-control study of prostate cancer that included comparable numbers of US Black and White men. The first manuscript examined the association between risk of prostate cancer and serum lycopene, a carotenoid found primarily in tomatoes that is an efficient quencher of singlet oxygen. Risk was reduced by 35% among men with serum lycopene concentrations in the highest relative to lowest quartile, with greater reductions observed for aggressive prostate cancer (p = 0.01). While associations were similar in Blacks and Whites, it was provocative that serum lycopene concentrations in Blacks were 18% lower than in Whites. Four other carotenoids, including β-carotene, were unassociated or positively associated with risk. The second manuscript focused on selenium, an essential trace element and contributor to the antioxidant enzyme glutathione peroxidase. Selenium was also inversely associated with prostate cancer risk for Black and White men, especially above a certain threshold concentration and when levels of serum α-tocopherol, a potent antioxidant and biomarker of vitamin E intake, were low. The third manuscript examined the relationship between prostate cancer risk and serum concentrations of α-tocopherol. Risk generally increased with higher serum concentrations of α-tocopherol in men of both races. However, when comparing very high to moderate levels, the association became inverse. In conclusion, a clear explanation for racial differences in prostate cancer incidence cannot be offered as a result of this research. However, several dietary hypotheses were supported and can now be extended to include US Blacks.