Selenium is a trace mineral, which means that our body requires only a small amount of selenium. This mineral is important for a healthy immune system, and it helps fight cancer. It is believed that selenium helps fight dementia, and that it is good for fertility.
Some of the richest sources of selenium are Brazil nuts, tuna, oysters, sunflower seeds, white rice and eggs. Brazil nut stands out as the richest source of selenium, but precise selenium content in this nuts depends on soil content.