The Selenium and Vitamin E Cancer Prevention Trial, or SELECT, was a
clinical trial
Clinical trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, dietar ...
conducted with the goal of determining whether
vitamin E
Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitami ...
and
selenium
Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
supplements could prevent
prostate cancer
Prostate cancer is cancer of the prostate. Prostate cancer is the second most common cancerous tumor worldwide and is the fifth leading cause of cancer-related mortality among men. The prostate is a gland in the male reproductive system that sur ...
.
[Selenium and Vitamin E Cancer Prevention Trial Q&A]
/ref> Enrollment for the trial began in 2001 and ended in 2004.[ It cost approximately $114 million to conduct and was performed at over 400 different research centers. It was primarily funded by the ]National Cancer Institute
The National Cancer Institute (NCI) coordinates the United States National Cancer Program and is part of the National Institutes of Health (NIH), which is one of eleven agencies that are part of the U.S. Department of Health and Human Services. ...
(NCI) and was carried out by SWOG
SWOG (formerly the Southwest Oncology Group) is a National Cancer Institute (NCI) supported organization that conducts clinical trials in adult cancers.
Comprising more than 4,000 cancer researchers at more than 650 institutions across the United ...
.[ It was stopped early because the supplements did not show any benefit in preventing prostate cancer. Subsequent research based on the trial has generally found that selenium and vitamin E do not prevent prostate cancer. Other research based on foods rich in selenium or Vitamin E, not supplements, suggests that there is limited evidence such foods may protect against some forms of cancer.
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Methodology
The study followed over 35,000 men in the United States, Puerto Rico, and Canada, who were assigned randomly to receive either both a selenium and vitamin E supplement, selenium and placebo, vitamin E and placebo, or two placebos. It was one of the largest cancer prevention trials ever conducted, and was described by the NCI as "the largest-ever prostate cancer prevention study."[Largest-Ever Prostate Cancer Prevention Trial Opens: 32,000 Men Sought to Test Vitamin E and Selenium]
/ref> Selenium and Vitamin E were chosen because they are well known antioxidants and had other mechanisms by which they were thought to prevent cancer, and preclinical and smaller clinical studies had yielded very promising results.[
The study was originally planned to last for twelve years after enrollment began.][ However, it was stopped early in 2008 because no protective effect of supplementation on prostate cancer risk was found, and because the results suggested that vitamin E might increase the risk.][ About 17,000 participants from the original SELECT completed an additional four years of a Centralized Follow-Up from 2010 until May 31, 2014, when SELECT closed. The follow-up involved sending questionnaires to participants annually, which they could also fill out online.][
]
Results
Initial results were published in 2008 in ''JAMA''. The initial results found that the increase in risk associated with Vitamin E was "statistically nonsignificant",[ which the researchers wanted to verify in a subsequent study.
A subsequent 2010 study further described SELECT's results and found that neither selenium nor vitamin E, on their own or in combination, prevented prostate cancer.
A 2011 study based on the trial found that the risk of prostate cancer was elevated by 17% in the group that took vitamin E supplements, which was statistically significant.]
A 2014 study based on SELECT data found that selenium supplementation increased the risk of high-grade prostate cancer in men who had a higher baseline selenium status.
A 2014 Cochrane review
Cochrane (previously known as the Cochrane Collaboration) is a British international charitable organisation formed to organise medical research findings to facilitate evidence-based choices about health interventions involving health professi ...
found that SELECT raised concerns about a possible association between selenium supplements and an increase in risk of type 2 diabetes
Type 2 diabetes, formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance, and relative lack of insulin. Common symptoms include increased thirst, frequent urination, ...
, alopecia and dermatitis
Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can v ...
. The review concluded that "no convincing evidence suggests that selenium supplements can prevent cancer in humans."
References
{{Reflist
Clinical trials related to cancer
Prostate cancer