Boosting the immune system is the first step in the prevention or treatment of any infection, and selenium is a key component in the functioning of our immune system. It acts as an antioxidant substance, and also stimulates the production of white blood cells, which are the body’s first line of defense. More importantly, it prevent the immune system from launching into a “cytokine storm”, when the body essentially attacks itself. Selenium-rich foods include tuna, Brazil nuts, oysters, pork and sunflower seeds.