Abstract
7 Background: The initial report of the Selenium and Vitamin E Cancer Prevention Trial (SELECT) found no reduction in risk of prostate cancer with either selenium or vitamin E supplements but a non-statistically significant increase in prostate cancer risk with vitamin E. Longer follow-up and more prostate cancer events provide further insight into the relationship of vitamin E and prostate cancer. Methods: SELECT randomized 35,533 men from 427 study sites in the United States, Canada and Puerto Rico in a double-blind manner between August 22, 2001 and June 24, 2004. Eligible men were 50 years or older (African Americans) or 55 years or older (all others) with a PSA <4.0 ng/mL and a digital rectal examination not suspicious for prostate cancer. Included in the analysis are 34,887 men randomly assigned to one of four treatment groups: selenium (n=8752), vitamin E (n=8737), both agents (n=8702), or placebo (n=8696). Data reflect the final data collected by the study sites on their participants through July 5, 2011. Results: This report includes 54,464 additional person-years of follow-up since the primary report. Hazard ratios (99% confidence intervals [CI]) and numbers of prostate cancers were 1.17 (99% CI 1.004-1.36, p=.008, n=620) for vitamin E, 1.09 (99% CI 0.93-1.27, p=.18, n=575) for selenium, 1.05 (99%CI 0.89-1.22, p=.46, n=555) for selenium + vitamin E vs. 1.00 (n=529) for placebo. The absolute increase in risk compared with placebo for vitamin E, selenium and the combination were 1.6, 0.9 and 0.4 cases of prostate cancer per 1,000 person-years. Conclusions: Dietary supplementation with Vitamin E significantly increases the risk of prostate cancer among healthy men.
Highlights
Interventions—Oral selenium (200 μg/day from L-selenomethionine) with matched vitamin E placebo, vitamin E (400 IU/d of all rac-α-tocopheryl acetate) with matched selenium placebo, both agents, or both matched placebos for a planned follow-up of a minimum of 7 and maximum of 12 years
Hazard ratios (99% confidence intervals [CI]) and numbers of prostate cancers were 1.17(99% CI 1.004-1.36, p=.008, n=620) for vitamin E, 1.09 for selenium, 1.05 (99%CI 0.89-1.22, p=.46, n=555) for selenium + vitamin E vs. 1.00 (n=529) for placebo.The absolute increase in risk compared with placebo for vitamin E, selenium and the combination were 1.6, 0.9 and 0.4 cases of prostate cancer per 1,000 person-years
A total of 521 additional prostate cancers have been diagnosed since the initial report: 113 in the placebo group, 147 in the Vitamin E group, 143 in the selenium group, and 118 in the combination group (Table 3)
Summary
Detailed descriptions of the rationale, design, conduct, and initial results of SELECT have been previously published.[6,7] The study enrolled healthy men at average risk of prostate cancer based on a baseline PSA of ≤ 4 ng/mL and normal digital rectal exam (DRE) commencing at age 50 for African Americans or age 55 for all others. A one-sided significance level of 0.005 was specified to test for the preventive effect for each supplement comparison and 99% confidence intervals are reported, we have reported two-sided p-values throughout because the comparison of prevention vs increased risk of cancer is a two-sided question.[6] A proportional hazards model was used to compare prostate cancer and other cancer incidence between placebo and each of the three arms with active agents. Those without the endpoint of interest were censored at their last contact date.
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