A prospective cohort study on toenail selenium levels and risk of gastrointestinal cancer.

BACKGROUND: Various animal studies and ecologic studies suggest an inverse association between low dietary selenium intake and risk of various types of cancer. PURPOSE: The goal of this prospective cohort study was to investigate the association between toenail selenium levels and risks of stomach cancer and colorectal cancer. METHODS: Our cohort study on diet and cancer started in The Netherlands in 1986 with enrollment of 120,852 subjects aged 55-69 years. Of this number, 58,279 were men and 62,573 were women. Following the case-cohort approach for analysis of the data, we randomly selected from the cohort a subcohort of 3500 subjects (1688 men and 1812 women). After 3.3 years of follow-up, 155 incident cases of microscopically confirmed stomach cancer, 313 cases of colon cancer, and 166 cases of rectal cancer had been detected in the cohort. Toenail selenium data were available for 104 patients with stomach cancer, 234 with colon cancer, and 113 with rectal cancer and for 2459 subjects from the subcohort. RESULTS: In a multivariate analysis, the relative rates (RRs) of stomach cancer for subjects in increasing quintiles of toenail selenium level were 1.00, 0.44, 0.59, 0.84, and 0.64 (trend, P = .491). For men, there was some evidence for an inverse association between toenail selenium levels and stomach cancer: The RR for those in the highest compared with the lowest quintile of toenail selenium was 0.40 (95% confidence interval = 0.17-0.96), but the trend was not statistically significant (P = .136). For stomach cancer in women, there was no negative association with toenail selenium levels. Toenail selenium level was not associated with the risk of colon or rectal cancer. After exclusion of cases diagnosed in the 1st year of follow-up, the RRs of colon cancer for increasing quintiles of toenail selenium were 1.00, 1.27, 1.17, 0.75, and 1.07 (trend, P = .544); for rectal cancer, RR estimates were 1.00, 1.73, 0.83, 1.58, and 1.12 (trend, P = .890). CONCLUSIONS: These data support a suggestive but inconsistent inverse association between selenium levels and risk of stomach cancer. Our findings, like those of other studies, do not suggest an inverse association with risk of colorectal cancer.