04/22/2014 03:43 pm ET Updated Jun 22, 2014

What Every Man Should Know About Supplements and Cancer

Most of us value our health and do what we believe will promote it. I say "believe" because much of people's behavior in the service of improving their health is based on faith, not fact. This is an understandable state of affairs where we lack the data. It is a curious thing when solid data is ignored.

Recent research now indicates that any healthy man who takes a common dose of vitamin E (400 IU) or selenium (200 mcg) may be increasing his risk for prostate cancer.

Turning a blind eye to information about alcohol or cigarettes is no mystery. We usually ignore directives that would rob us of a pleasurable or addictive habit. But to similarly ignore data about something we use expressly to promote our health, that provides no pleasure, is not as easily understood.

About half of adult Americans take a supplement daily. Between 1996 and 2006 supplement sales increased by 100 percent. In 2010, Americans spent $28 billion on these products. This is all the more remarkable because during this same period reputable research repeatedly demonstrated the failure of supplements to prevent the occurrence or progression of any major illness such as cardiovascular disease or cancer.

Surveys have shown that the people who take supplements are for the most part educated, have good incomes, and eat sensibly. This is a population that is least likely to have deficiencies of vitamin E or selenium. Ironically, the increased risk for prostate cancer associated with supplementation of these nutrients is thought to be a result of supraphysiological (higher than normal) levels.

In other words, well-educated, economically-comfortable men who eat sensibly are most vulnerable to the cancer inducing effects of these supplements.

It is of note that interest in this area began with laboratory research suggesting that vitamin E and selenium might decrease the risk of prostate cancer. This data lead to the Selenium and Vitamin E Cancer Prevention Trial (SELECT). In 2001, 35,533 healthy men were randomized into four groups, selenium with matching placebo, vitamin E with matching placebo, both agents, or placebo alone. Data analysis in 2008 revealed no risk reduction. In fact there appeared to be an increased risk of prostate cancer in the vitamin E plus placebo group that approached statistical significance.

In 2011, Klein et. al. provided a follow-up report. The data now demonstrated that healthy men with average risk of prostate cancer who took a common dose and formulation of vitamin E (400 IU/d) had a significantly increased risk (17 percent) of prostate cancer. Selenium supplementation appeared to have no effect. Both findings were unexpected.

A previous study, the Nutritional Prevention of Cancer Trial (NPC), had found that supplementation in men with moderate and low selenium levels appeared to significantly decrease risk for prostate cancer. No effect on men with high selenium levels was observed.

In the most recent addition to this story, investigators sought to clarify the effect of pre-study selenium levels in SELECT subjects. They wanted to revisit the question of how vitamin E and selenium interact. This combination was known to have a synergistic effect on cancer prevention in some animal models.

Again, the results were unanticipated. They observed no association between selenium levels and prostate cancer in the absence of supplementation. Selenium supplementation did not benefit those with low selenium levels. The Vitamin E results were more troubling. Supplementation with vitamin E increased the risk of prostate cancer among men with low selenium levels. For those with high selenium levels, both selenium alone and selenium plus vitamin E increased the risk of high-grade prostate cancer.

Prostate cancer is the second leading cause of cancer death in American men. In 2014 233,000 new cases will be diagnosed and 29,480 will die of this disease. Most cases of prostate cancer are diagnosed early and can be successfully treated. The cure however can be costly. Incontinence and impotence caused by treatment is common. For a man to increase his risk for this disease by taking supplements hoping to enhance his health is tragic.

Supplements are not benign agents that can only help or at worst do nothing. A growing literature suggests that the effect of supplementation is largely defined by the nutrient status of the individual. Supplementation of those with adequate nutrient status can increase cancer risk. Surveys indicate that this is who takes supplements.

What can be drawn from these findings?

Clearly, our biology is complex. It is particularly unsettling to find that replenishing low levels of an important compound with supplements causes harm. For instance, we know that oxidation can cause disease. To assume that supplementing a low antioxidant (vitamin E or selenium) level would have beneficial effects is logical. It may even work in a test tube or lab animal. However, this research adds to a growing literature that suggests that antioxidant supplementation can be harmful.

The investigators recommend that men aged greater than 55 should avoid supplementation at doses that exceed recommended dietary intakes for vitamin E (22.4 IU/day) and selenium (55 mcg/day).

Too much of a good thing could kill you.