Selenium has been shown to prevent some cancers but it has been proven to increase melanoma. Selenium Boosts the immune system, improves thyroid health, Asthma, promotes sperm count and blood flow. Selenium also protects your body from wearing down and feeling older than it really is. Selenium has been shown to reduce oxidative stress that often occurs around joints and bones, manifesting into the various inflammatory conditions  like rheumatoid arthritis, gout, psoriasis, lupus, eczema associated pain, and weakness. It can also help with your mood and mental health, it's antioxidant rich, improves heart health, and treats Kashin-Beck disease. There are many benefits to taking Selenium but you really need to be careful on the dosage. I'm am very pleased with this brand from Amazon, Pure Healthland. It's a USA company and it provides top quality selenium that it yeast and chemical free. They also offer a money back guarantee.