While selenium is itself an antioxidant, it is also vital for the formation of one of the body's key antioxidants. This antioxidant activity is believed to be responsible for selenium's reported ability to protect against heart attacks and strokes while supporting overall cardiovascular health. However, a study involving 153 people with coronary artery disease and low HDL (good) cholesterol questioned these benefits. The antioxidants vitamin C, vitamin E, beta-carotene and selenium were added to cholesterol treatment of simvastatin and niacin and continued to show improvement over placebo, but decreased the benefits seen on HDL cholesterol measurements from simvastatin and niacin without the antioxidants.(
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Also, studies have linked low dietary selenium intake with lower rates of several types of cancer such as rectal, prostate, breast, intestinal, ovarian, lung and leukemia.(4),(5),(6) A study found that selenium supplementation to patients suffering from cancer of the digestive tract may improve nutritional status and increase appetite.(7) High levels of selenium were found to decrease the incidence of skin cancer.(8) Selenium compounds may be useful as cancer chemopreventive agents.(9) One study found that higher intake of selenium increased the risk of cancer.(10) Results from a large trial found that selenium did not reduce the risk of cancer.(11)
Selenium may also have anti-viral properties by enhancing the body's cellular defenses.(12),(13) It may also help rid the body of heavy metal toxins like mercury and cadmium.
Targeted clinical applications for selenium include use in the fight against AIDS, bronchial asthma and cataracts.(14),(15),(16) The risk of type 2 diabetes was 50% higher among participants taking selenium compared to those taking a placebo.(17) Low serum selenium was associated with anemia in older adults.(18)