An updated review of data from the Selenium and Vitamin E Cancer Prevention Trial (SELECT) concluded that men who took 400 international units of vitamin E daily had more prostate cancers than men who took a placebo.
The findings showed that over a 7-year period there were 76 prostate cancers per 1,000 men who took only vitamin E supplements vs. 65 per 1,000 men on placebo, or 11 more cases of prostate cancer per 1,000 men. This represents a 17 percent increase in prostate cancers relative to those who took a placebo. This difference was statistically significant and therefore is not likely due to chance.
These findings are published in the Oct. 12 issue of the Journal of the American Medical Association. The NIH-funded study was designed and conducted at more than 400 sites in the U.S. and Canada by the SWOG clinical trials cooperative group, which is headquartered at the University of Michigan.
The SELECT study began in 2001 and included more than 35,000 men. It was started because earlier research had suggested that selenium or vitamin E might reduce the risk of developing prostate cancer. But an independent safety monitoring review of SELECT data in autumn 2008 concluded that the trial would never produce the 25 percent reduction in prostate cancer the study was designed to show, and participants were told to stop taking their study supplements.
In 2010, the study sites were closed and more than half of the participants consented to have their health monitored via mail questionnaires. Now, because of this latest finding, researchers are encouraging all participants to consider taking part in long-term study follow-up so investigators can continue to track outcomes.
“Based on these results and the results of large cardiovascular studies using vitamin E, there is no reason for men in the general population to take the dose of vitamin E used in SELECT, as the supplements have shown no benefit and some very real risks,” says Eric Klein, M.D., a study co-chair for SELECT, and a physician at the Cleveland Clinic. “For now, men who were part of SELECT should continue to see their primary care physician or urologist and bring these results to their attention for further consideration.”
SELECT was undertaken to substantiate earlier, separate findings from studies in which prostate cancer risk was not the primary outcome being assessed: a 1998 study of male smokers in Finland who took 50 international units of vitamin E daily to prevent lung cancer, surprisingly showed 32 percent fewer prostate cancers in men who took the supplement; and a 1996 study of men and women with a history of skin cancer who took selenium for prevention of disease recurrence showed that men who took the supplement had 52 percent fewer prostate cancers than men who did not take the supplement.
Based on these and other findings, men were recruited to participate in SELECT. They were randomly assigned to take one of four sets of supplements or placebos, with more than 8,000 men in each group.
One group took both selenium and vitamin E; one took selenium and a vitamin E placebo; one took vitamin E and a selenium placebo; and the final group received placebos of both supplements. Men who took selenium alone or vitamin E and selenium together were also more likely to develop prostate cancer than men who took a placebo, but those increases were small and possibly due to chance.
SELECT researchers are now measuring the amount of vitamin E, selenium, and other nutrients in blood samples participants gave when they joined the trial to see if the effect of the supplements depended upon this baseline level of micronutrient.
Other researchers are looking at single nucleotide polymorphisms, or DNA changes known as SNPs, to see if a change in one or more genes could affect cancer risk or perhaps increase a man’s risk of developing prostate cancer while taking vitamin E.
The participant samples come from the study biorepository of blood and toe nail clippings which, when coupled with the extensive clinical information on participants, is a vital resource for further study.
“SWOG is soliciting proposals from researchers nationwide to use the SELECT biorepository to help answer the biological question of why vitamin E increased risk instead of decreasing it,” says Laurence Baker, D.O., study co-author and chairman of SWOG. “There are many more questions raised by these study results than we have answers for, and thus the need for further investigation.” Dr. Baker is also a professor of internal medicine and pharmacology at the U-M Medical School.
Except for skin cancer, prostate cancer is the most common type of cancer in men in the United States. The current lifetime risk of prostate cancer for American men is 16 percent.
In 2011, there will be an estimated 240,890 new cases of prostate cancer and 33,720 deaths from this disease in the U.S.
SELECT has been funded by NCI with additional monies from the National Center for Complementary and Alternative Medicine, and with sub-studies funded and conducted by the National Heart, Lung, and Blood Institute; the National Institute of Aging; and the National Eye Institute at NIH.
“SELECT has definitively shown a lack of benefit from vitamin E and selenium supplements in the prevention of prostate cancer and has shown there is the potential for harm,” says Lori Minasian, M.D., study co-author and acting director of NCI’s Division of Cancer Prevention. “Nevertheless, this type of research has been critically important to understanding the potential benefits and risks from supplements.”
Reference: EA Klein, IM Thompson, CM Tangen, JJ Crowley, MS Lucia, PJ Goodman, L Minasian, LG Ford, HL Parnes, JM Gaziano, DD Karp, MM Lieber, PJ Walther, L Klotz, JK Parsons, JL Chin, A Darke, SM Lippman, GE Goodman, FL Meyskens, and LH Baker. Vitamin E and the Risk of Prostate Cancer: The Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. October 12, 2011.
For an updated Q&A on SELECT, please go to http://www.cancer.gov/newscenter/qa/2008/selectqa.
For a Spanish version of the release and Q&A, please go to http://www.cancer.gov/espanol/noticias/SELECT2011Spanish.
To view a schematic drawing of the prostate, a microscopic view of the crystal structure of vitamin E, and photos of the pills that were provided to the SELECT participants, please go to http://www.cancer.gov/newscenter/pressreleases/2001/select.
To view a graphical representation of the increase in prostate cancer risk found in the SELECT date, please go to http://swog.org/Media/Newsroom.asp.
SWOG (formerly the Southwest Oncology Group) is one of the largest cancer clinical trial cooperative groups in the United States. Funded primarily by the National Cancer Institute, the group designs and conducts clinical trials to improve the practice of medicine in preventing, detecting, and treating cancer, and to enhance the quality of life for cancer survivors. The more than 4,000 physician-researchers in the group’s network practice at more than 500 institutions, including 19 of the National Cancer Institute-designated cancer centers. The Group is headquartered at the University of Michigan in Ann Arbor, Mich. (734-998-7140), and has an operations office in San Antonio, Texas, and a statistical center in Seattle, Wash. Learn more at swog.org. SWOG – Leading cancer research. Together.