The selenium and vitamin E cancer prevention trial (SELECT): a secondary, post-intervention analysis on potential excess chronic disease incidence induced by selenium administration.

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The potential for trace amounts of selenium supplements to prevent prostate cancer and other neoplasms was studied in SELECT, a randomized trial conducted in North America for 7-12 years. 34 887 eligible men age 55 or older were assigned to take either 200 μg selenium from L-selenomethionine, 400 IU vitamin E, both selenium and vitamin E, or placebo. The trial was stopped for futility and concerns about adverse effects. Subsequently, we used incidence and mortality data from Medicare through 2019 and the National Death Index through 2024 to investigate the extent to which selenium administration was associated with increased long-term risk of cancer and neurodegenerative disease, during 341 697 person-years of follow-up. Lung cancer showed little increased risk. Associations were near null for leukemia, non-Hodgkin lymphoma and Parkinson's disease, and there was a lower risk for melanoma and colorectal cancer. In contrast, we found a higher risk for Hodgkin lymphoma, multiple myeloma and amyotrophic lateral sclerosis, which has been associated with selenium overexposure in some nonexperimental studies. Though these latter associations were based on few cases, they were consistent with findings from a range of other studies, possibly indicating long-term adverse effects of this organic selenium compound. (Registration no. NCT00006392).

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