The study, called SELECT (the Selenium and Vitamin E Cancer Prevention Trial), found that men who took 400 IU (international units) of vitamin E each day were 17 per cent more likely to develop prostate cancer than non-vitamin-E users.
Findings from earlier studies investigating supplements and the risk for other types of cancer had suggested that supplemental vitamin E and selenium guarded against prostate cancer. In 1998, a Finnish study of male smokers who took 50 IU of vitamin E daily in hopes of preventing lung cancer surprisingly found 32 per cent fewer prostate cancers among vitamin-E users.
In 2001, SELECT set out to substantiate these observations. The trial assigned 35,533 healthy men aged 50 and older to four treatment groups: 400 IU of vitamin E daily, 200 micrograms of selenium daily, both supplements daily, and placebo.
An earlier analysis, published in 2008, found no benefit – vitamin E and selenium, taken alone or in combination, did not prevent prostate cancer. And there were two worrisome trends: a small increase in the number of prostate cancers among vitamin-E users and a small rise in Type 2 diabetes among men taking selenium. Neither finding was statistically significant, meaning it may have been a coincidence.
The trial was discontinued early and men were told to stop taking their supplements.
Since 2008, SELECT investigators have continued to follow participants and gather additional data to determine any long-term effects of supplements on prostate-cancer risk.
Today’s report noted that the rate of prostate cancer was 17 per cent greater in the vitamin-E group, a finding that was statistically significant. There was no increased risk of prostate cancer when vitamin E and selenium were taken together, suggesting that selenium somehow dampens the harm caused by vitamin E.
The fact that the increased risk of prostate cancer was only evident after extended follow-up suggests the health effects from these supplements may continue even after men stop taking them.
The updated SELECT results found no link between selenium supplements and Type 2 diabetes risk. The longer follow-up did not demonstrate a benefit for either supplement in the risk of colorectal or lung cancer or cardiovascular events.
If you take vitamin E in the hope of warding off chronic disease, it’s time to trade it in for a healthy diet. Clinical trials have not demonstrated any benefit regarding heart attack, death from heart disease, colorectal polyps, respiratory infections in the elderly, or progression of cataracts or macular degeneration.
Moreover, the increased risk of prostate cancer seen in SELECT, the previously reported higher risk of lung cancer with high-dose beta carotene, and the greater risk of colon polyps seen with high-dose folic acid supplements strongly suggest using caution when taking supplements.
Findings published yesterday in the Archives of Internal Medicine also raise concern over the long-term safety of certain supplements. The study followed 38,772 older women for 19 years and found several common supplements, most notably iron, were associated with a greater risk of death. (Calcium and vitamin D were associated with a lower risk.)
Data regarding the harmful effects of dietary supplements were limited until recently. It’s now becoming clear that more is not better. There are risks associated with consuming too little of a nutrient and too much. A low intake can lead to deficiency, and a high intake may lead to toxic effects and disease.
In my opinion, supplements are meant to bridge nutrient gaps in a healthy diet. A multivitamin can help menstruating women and vegetarians meet iron requirements and older adults get enough vitamin B12. If you need a multivitamin, choose a standard one-a-day formula that offers 100 per cent of the recommended daily intake for most nutrients. Avoid “mega” or “super” formulas, which can contain high amounts of antioxidants, B vitamins and minerals.
Adults will also benefit from taking vitamin D3 if they don’t get enough from the sun or diet. To help ensure a sufficient blood level of vitamin D, Canadians are advised to take 1,000 IU daily in the fall and winter, and all year if they are over 50, have dark skin, don’t go outdoors often, or wear clothing that covers most of their skin.
But vitamin and mineral supplements do not prevent disease – at least not in well-nourished people. That said, a supplement containing vitamins C and E, lutein and zinc has been shown to slow the progression of intermediate and advanced macular degeneration. And it’s well established that taking folic acid, a B vitamin needed for healthy cell division, before and during the early weeks of pregnancy is vital to preventing neural tube defects.
Reducing your risk of chronic disease requires eating right as well as maintaining a healthy weight and exercising regularly. Large studies have consistently shown that a diet based on fruit and vegetables, whole grains, legumes and unsaturated vegetable oils reduce the risk of high blood pressure, heart disease, stroke, osteoporosis, Type 2 diabetes and certain cancers.
No supplement can replace the benefits of a healthy diet. Whole foods provide vitamins, minerals, protective phytochemicals and fibre, all of which likely work together to fend off disease.
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV’s Canada AM every Wednesday. Her website is lesliebeck.com.