This is one mineral that should be on everyone's supplement list. As most of the U.S. soil is deficient in selenium. Some of the problems from a deficiency of selenium are age spots, ALS, cardiomyopathy, cataracts, cancer risk, cystic fibrosis, fatigue, growth retardation. high infant mortality, HIV to AIDS MS, Muscular dystrophy, Keshan disease [myocardial fibrosis] and even more. The supplement industry went to the FDA to show tons of evident that selenium help prevent cancer. The FDA controlled by big pharm fought but the evidence was over whelming they gave in and allowed the supplement makers to put on the bottle [May reduce the risk of certain forms of cancer] Land mark decision. Not long after that Big Pharma came out with a study saying selenium causes cancer. Which turned out to be untrue but they still quote that study.
Also, selenium has been shown to have anti-viral properties. We eat 2 whole Brazil nuts every morning with breakfast to get extra natural selenium.