The human body contains, on average, only about 14 mg of the trace mineral selenium, but that 14 mg plays important roles in the function and growth of every cell in the body. Selenium is involved in the production of ATP for energy storage in the mitochondria, in immunity, and in the production of coenzyme Q-10.
Before about 1960, selenium was assumed to be toxic. That's because, to cattle and goats grazing in the semi-arid western United States, it sometimes is.
Selenium is not distributed evenly in rocks and soils. Plants take up selenium from the ground and pass the element up the food chain.
In the case of selenium-intoxicated goats in Wyoming, some plants get a super-dose of selenium that's incorporated into the tissues of the animals that eat them. Far more often, selenium simply is not found in abundance in the natural soils used for farming (and this has nothing to do with good or bad farming practices, the selenium is there or it isn't).
Wheat grown in the US, for instance, has much higher, and healthier, concentrations of selenium than wheat grown in other parts of the world. And Brazil nuts, in particular, are a superb source of selenium both because of the unique physiology of the tree they grow on and the mineral concentrations of soils in Brazil.
Selenium is well-known as a nutrient important for cancer prevention.
There are certain cancers selenium doesn't seem to affect. Basal cell and surface squamous cell skin cancer seem to develop independently of dietary selenium.
Colorectal, lung, and prostate cancers, on the other hand, occur less frequently and are survived longer in people who take selenium supplements. A combination of selenium and anti-inflammatories may ameliorate the progression of esophageal squamous cells cancer.
In parts of China where selenium deficiency is common (due to selenium deficiency in the soils), there's an unusual incidence of a condition called Keshan disease. This is a kind of cardiomyoapthy, destruction of the heart muscle with enlarged heart and poor heart function. Keshan disease occurs where selenium intake is about 16 micrograms a day, which is about half the RDA.
A lot of preliminary research suggests that the way selenium is heart-protective works something like this:
- Selenium helps the body conserve the antioxidant glutathione.
- Glutathione keeps LDL cholesterol from oxidizing into a form that "sticks" in the lining of blood vessels.
- When LDL stays in circulation, it is consumed by the "germ eating" white blood cells known as macrophages in the bloodstream.
- When LDL gets "stuck," it's consumed by macrophages that also get stuck in the lining of the artery, causing plaque and calcification and increasing the risk of a clot.
There's also some evidence that getting enough selenium may slow the progression of diabetes.
For the overwhelming majority of diabetics, those who have diabetes type II, the primary cause of high blood sugars is insulin resistance. (Type I diabetics can develop insulin resistance, too, but it is not the primary reason for their high blood sugars.)
Insulin resistance is basically just a protective mechanism. When blood sugar levels are high, some of the glucose "burns" before it even gets inside a cell. To protect their interiors against this "burning" (free-radical generating) glucose, muscle and liver cells develop "resistance" to the action of insulin to keep glucose out.
This saves the insides of the cells from oxidation, but it also makes the problem worse and blood sugars get even higher and muscle and liver cells become even more insulin resistant.
Selenium may help break the cycle. Proteins containing selenium may capture some of the free radicals generated by the auto-oxidation of glucose so that muscle and liver cells don't have to become as insulin-resistant.
In arthritis, selenium may be helpful by stopping what is called the arachidonic acid cascade.
In arthritis and in every other condition, both "good" and "bad" fatty acids play a role in tissue regulation. The "good" fatty acids promote tissue regeneration, and the "bad" fatty acids promote inflammation (which is sometimes a good thing, as when the body is getting rid of an infection).
The problem in arthritis is that the "bad" pro-inflammatory fatty acids are produced in overabundance. Selenium tilts the balance of fatty acids back to the anti-inflammatory side.
This is also how selenium may be helpful in infection. Often the damage associated with an infection is not caused by the infectious microorganism itself, but by the immune system's over-reaction to the infection. Selenium dampens the production of inflammatory chemicals by the body itself.
Sometimes tissue integrity is a "signal" to the infection that the tissue is not ready to be consumed, and selenium-sufficiency can reduce the risk of viral mutation.
The most common and best-known application of selenium in natural health, however, is in skin care. The well-known "blue shampoos" for dandruff and rinses for athlete's foot and seborrheic dermatitis also contain selenium compounds. And selenium in sunblock protects the skin against UV radiation.
So does this mean you should run out and buy the most expensive selenium supplement you can find? No, two Brazil nuts a day really will do the trick. And if you can't eat nuts, four ounces (110 g) of fish or shellfish also provides a day's supply of selenium. Brown rice, oatemal, beans and peas, brewer's yeast, and eggs are also good source of this mineral.
Would you like to read the research literature for yourself?
A good place to start is with the earlier studies of how various sources of selenium support antioxidant status. You can find an original research article published in the American Journal of Clinical Nutrition here. You can read an abstract of the research study that found that selenium didn't especially help skin cancer prevention, but apparently did stop the progression of colon, lung, and other cancers here. And you can read where the upper limit for selenium supplementation for people at risk for skin cancer should be below 200 micrograms a day here.