Selenium is a trace mineral that, in it's organic form, is stored by the body. When it bonds with some proteins, it forms selenoproteins, which are antioxidant enzymes, and regulate thyroid activity and effect the immune system.
Selenium is best absorbed in it's organic form, which is acquired in plants and animals, but it depends on the selenium levels found in the soil. Selenmethionine is stored in muscles and tissues. It stimulates the immune system, helpful in the fight against cancer and arthritis, reduces aging, reduces cardio-vascular disease, strokes and heart attacks, lowers blood clotting, increases elasticity of skin, is an aphrodisiac, helps fertility, reduces tobacco damage, and when applied topically has antibacterial and antifungul effects so is good for dandruff and age spots as well. These are the claims anyway.
A deficiency can lead to heart disease, weakened immune system, hypothyroidism, cataracts, muscular dystrophy, retarded growth, liver problems, infertility, some forms of cancer, Kashin-Beck disease, Keshan disease, Myxedematous Endemic Cretinism. A deficiency often does not cause disease, it just makes one more susceptible. Severe gastro-intestinal problems (such as Crohn's disease) depletes all nutritional absorption, and being on total parenatal nutrition (TPN), that is being fed only by a drip, can reduce selenium if not properly distributed. High levels of selenium leads to selenosis, which has the symptoms of gastro-intestinal upsets, blotchy white nails, hair loss, "garlic breath", irritability, fatigue, and nerve damage.
It is found in brazil nuts (has a high level), tuna, beef, cod, turkey, chicken, pasta, egg, cottage cheese, oatmeal, rice, wholegrains, walnuts, and cheese. Corn, wheat and soyabeans have selenomethionine.