According to Bruce Ames, Ph.D., of the University of California, Berkeley, when certain vital micronutrients are in short supply, the body undergoes slow, insidious changes that undermine health and increase the risk of chronic disease.

One such crucial micronutrient is selenium. Dr. Ames and his fellow researchers recently analyzed 25 studies to judge the activity of immune-system components called selenoproteins – which, as the name suggests, contain selenium as an essential component. His conclusion? Even “modest” selenium deficiency appears to be associated with age-related diseases and conditions such as cancer, heart disease and immune dysfunction.

Excellent dietary sources of selenium include Brazil nuts (in fact, these should be eaten only occasionally, as their unusually high levels of this vital mineral could lead to an overdose, according to the National Institutes of Health). Other dietary sources include brewer’s yeast, wheat germ, garlic, truly whole grains, sunflower seeds, walnuts, raisins, shellfish, and both fresh and saltwater fish. If you need it in supplement form, I recommend an organic form such as yeast-bound selenium or selenomethionine. It is commonly paired with zinc for thyroid hormone support.