Selenium is a trace mineral you need for antioxidant activity, thyroid hormone metabolism and immune-system competence. Selenium may be either inorganic or organic, with the latter kind found in foods such as nuts, whole grains, brown rice, seafood and yeast. An example of inorganic selenium is sodium selenite. In the more desirable organic, or nutritional, form, selenium is complexed with amino acids such as methionine and cysteine. The selenomethionine form is considered the most desirable in terms of safety and absorption.
At one time selenium was considered a toxic substance and possible carcinogen. More recent research, however, shows that it’s one of the most potent nutrient protectors against various types of cancer. For example, one study showed that taking 200 micrograms of selenium daily led to a 66 percent decreased risk of prostate cancer, a 50 percent decreased risk of colon cancer and a 40 percent decreased risk of lung cancer. Around 200 micrograms a day is a good supplemental dosage.
Scientists first noted the connection between selenium and cancer by observing that in regions of China where the soil, and thus the food, is selenium-depleted, inhabitants had unusually high rates of cancer. In one region there was a high rate of a type of heart disease that comes from a deficiency of selenium coupled with the Coxsackie virus.
Selenium’s antioxidant function comes mainly from its incorporation into and activation of glutathione peroxidases, a set of enzymes that work by neutralizing excess hydrogen peroxide, preventing it from acting as a free radical. Glutathione peroxidase helps protect such vital structures as cellular membranes, which are largely composed of fat. Selenium also activates another set of enzymes, thioredoxin reductases, that help regenerate vitamin C after it’s been oxidized, thus helping you get more bang for your vitamin C buck.
Selenium is required for the full expression of various immune-system components, such as T cells and cytokines. The combination of antioxidant and immune-stimulation activity is what accounts for its protective role against cancer. Some studies show that cellular content of selenium determines the spread of HIV in the body, and others show that selenium may help protect against influenza.
In relation to cardiovascular disease, the mineral offers several beneficial effects. As an antioxidant it helps prevent the oxidation of low-density lipoprotein (LDL) in the blood. That’s significant because LDL, often called the ‘bad’ cholesterol, is dangerous only when oxidized. Selenium prevents excess platelet aggregation, which leads to arterial clotting, the cause of most heart attacks.
Those who worry about the environmental ubiquity of toxic heavy metals, such as cadmium, arsenic and mercury, would be wise to make sure they’re getting enough selenium; heavy metals are implicated in both cancer and cardiovascular disease. Cadmium is linked to prostate cancer, while mercury is showing up with increased frequency in an otherwise healthful food, fish. Selenium speeds their exit from the body by displacing them and neutralizing their effects.
Selenium may also help increase male fertility. One form of glutathione peroxidase not only acts as an antioxidant in sperm but also maintains its structure.