A case-control study of toenail selenium and cancer of the breast, colon, and prostate

To study the possible role of dietary and supplementary selenium intake in the etiology of cancer, we carried out a case-control study of breast, colo n, and prostate cancer in Montreal between 1989 and 1993. In this study, we were able to interview a total of 1,048 incidence cases of colon (402), br east (414) and prostate (232) cancer subjects and 688 population-based cont rols matched for age and gender. Of these, a total of 501 cancer cases and 202 controls produced toenail samples for their selenium concentrations, wh ich were determined by neutron activation analysis. We found no association between toenail selenium and breast cancer (odds ratio [OR], 0.72; 95% con fidence interval [CI], 0.4-1.31) or prostate cancer (OR, 1.14; 95% CI, 0.46 -2.83), though we did observe a statistically significant inverse associati on between toenail selenium level and the risk of colon cancer for both gen ders combined (OR, 0.42; 95% CI, 0.19-0.93; P =.009) and for female subject s (P =.050). We also found that nonsmoker case and control subjects had hig her selenium in their toenail samples. This could be due either to the natu re of tobacco, which reduces selenium absorption, or to smokers' consumptio n of certain foods containing less selenium. Further epidemiologic studies are required to clarify the role of selenium in the etiology of certain can cers.