According to the investigators, previous research has suggested that men who already have an adequate intake of selenium would not benefit from supplements of the nutrient.
Selenium is a chemical element most commonly found in seafood and organ meats, such as liver. Other food sources of selenium include muscle meats, cereals and dairy products. The National Institutes of Health state that selenium is nutritionally essential for humans and plays roles in reproduction, thyroid hormone metabolism and DNA syntheses, as well as protects against oxidative damage and infection. According to the Food and Nutrition Board, the recommended dietary allowance for both males and females aged 14 years and over is 55 mcg per day.
Vitamin E is a group of fat-soluble compounds that act as an antioxidant in the body. The vitamin is commonly found in foods such as nuts, seeds, vegetable oils, green leafy vegetables and fortified cereals.
For the study, the researchers wanted to determine whether taking daily high doses of vitamin E (400 IU) and/or selenium (200 mcg) may reduce the risk of prostate cancer. The findings revealed that men who had high selenium levels at the beginning of the study had a 91% increased risk of high-grade prostate cancer. According to the researchers, the levels of selenium for these men became toxic.
The investigators also found that for men with low selenium levels at the baseline of the study, vitamin E increased total prostate cancer risk by 63%, while high-grade prostate cancer risk increased by 111%. Many people think that dietary supplements are helpful or at the least innocuous. This is not true. Researchers add that people taking vitamin E or selenium supplements should stop because there is no evidence that they produce any health benefits - only risks.
Taking a broad view of the recent scientific studies, there is an emerging consistency about how we think about optimal intake of micronutrients. There are optimal levels, and these are often the levels obtained from a healthful diet, but either below or above the levels there are risks.