The idea that selenium protects against prostate cancer got its start when a small study found that men with skin cancer who were given selenium supplements had 52 percent fewer prostate cancers than men who did not take the supplement.
Another study, which examined the effects of vitamin E on the prevention of lung cancer in about 29,000 male smokers in Finland, observed that the men who took vitamin E had 32 percent fewer prostate cancers.
Prevention of prostate cancer was not a primary aim of either study. And yet the results of these two studies led the National Cancer Institute and other NIH institutes to invest large amounts of taxpayer money to initiate the SELECT trial, examining the effect of both vitamin E and selenium in more than 35,000 men age 50 or older.
Participants were randomly divided into four equal-sized groups; each group took one of the following treatments each day: Group 1, selenium (200 μg) and vitamin E (400 IU); Group 2, selenium (200 μg); Group 3, vitamin E (400 IU), and Group 4, double placebo.
Trial enrollment started in 2001 at more than 400 clinical sites in the US, Puerto Rico, and Canada. The plan was to administer the supplements for at least 7 years or a maximum of 12 years. Thus, final results were not expected until 2013; however, the trial was stopped in 2008 because analysis of the data obtained during the first 5 years found that men taking the supplements, either alone or together, had no lower risk of prostate cancer.
These early results also showed two concerning trends: a small, not statistically significant increase in the number of prostate cancers among the men taking only vitamin E, as well as a small but not statistically significant increase in the number of cases of type 2 diabetes in the men taking only selenium. Chance alone may have accounted for both of these adverse trends.
About a week ago, I watched a television ad that promoted a particular multivitamin that would help to prevent prostate cancer because it contained selenium. In view of the failure of selenium to prevent prostate cancer in the SELECT trial, I would hope that ad will be discontinued and that men, in the hope of avoiding prostate cancer, won't be tempted to take selenium-containing vitamin pills or any other type of selenium supplements.
The study also puts to rest another proposed benefit of the antioxidant effects of vitamin E, which has now been shown to be ineffective in the prevention of
- coronary heart disease
- Alzheimer's disease
- prostate cancer
- various other cancers
Some studies have even shown increased overall mortality in people taking vitamin E supplements. And yet, millions of people in the U.S. still take supplements of this vitamin.
Scientists at the Linus Pauling Institute at Oregon State University argue that all the studies on vitamin E are flawed because much larger doses of the vitamin are required to achieve the desired preventive goals. Although their conclusions, based on theoretical considerations, may be correct, larger doses of vitamin E might further increase the higher overall mortality already seen in people taking smaller doses of it. I strongly recommend that people refrain from taking any doses of vitamin E at all—especially ones much larger than 400 IU—until clinical trials show clear benefits and the absence of adverse side effects.
And be careful about selenium supplements. The FDA has gotten reports of serious side effects (hair loss, muscle cramps, diarrhea, joint pain, deformed fingernails, and fatigue) in people taking certain flavors of Total Body Formula and Total Body Mega Formula, which contain hazardous levels of selenium—more than 200 times the amount per serving indicated on product labels.
