Selenium, symbol Se, is one of the trace minerals and according to the Food and Nutrition Board of the National Academy's Institute of Medicine we only need 55 ug per day.
Given that, one might wonder how we could not get enough in our normal everyday diet?
Natural Food Sources
Without a doubt we get a lot of selenium in much of the food we consume.
According to the Agricultural Research Service of the USDA, just one ounce of dried Brazil nuts has 544 ug; 3 ounces of canned light tuna in oil have 63 ug, 3.5 ounces of cooked beef has 35 ug, 3.5 ounces of chicken breast has 20 ug and one medium egg has 14 ug.
That's in the U.S. but in most of the world; people rely on plant foods for this important mineral. The problem is that the plant content depends on the soil content and in parts of China and Russia, the soil is so poor that deficiencies are common.
In the U.S. the plains of Nebraska and the Dakotas the soil is very high in Se so whatever crops are grown or whatever the cattle and other range animals graze on gives both meat and plants, a very high content.
Furthermore the widespread food distribution system in the U.S. insures that food grown in the plains areas get into supermarkets across the country. Deficiency in the U.S. is rare. The entire content of Se in the human body is between 13 and 20 mg.
Why is there a Deficiency?
Given that, why are we even talking about supplementing this particular mineral?
A healthy person, eating a fairly balanced diet would not need to use a supplement. Nevertheless, there are several health conditions that do create deficiencies.
They include a compromised digestive system such as seen in Crohn's disease, ulcerative colitis, inflammatory bowel disease and the like. Also people living solely on intravenous feeding will be at risk of deficiency as well as geriatrics over the age of 90.
Selenium and Health
Research has uncovered several very important roles regarding our health. It is a component of two amino acids that are present in several enzymes that enable anti-oxidant activity.
In particular the family of glutathione peroxidases which neutralize certain reactive oxygen species such as hydrogen peroxide and other organic peroxides depend on it.
Another function of this trace mineral is the proper functioning of the thyroid gland. Every cell in the body that uses a thyroid hormone requires a selenium cofactor to enable the three enzymes that activate or deactivate the various thyroid hormones.
Considering the thyroid gland, Hashimoto's disease is an autoimmune condition in which the body's own thyroid cells are attacked as alien intruder cells.
A 2007 issue of the Journal of the American Thyroid Association reported on a research project in which a dietary intake of .2 mg resulted in a 21% reduction in the antibodies causing this disease.
Since Se is not a mineral that needs to be supplemented under normal conditions, why mention it here at all?
We included it here because there is a danger of overdosing on it by people who have read that it is good for their enzyme action or thyroid function. So they pick up a supplement at the local drugstore supplement section and start taking them.
The supplement content is generally in the 200 ug range and if they eat normally, the content in their food could quickly take them over the Tolerable Upper Intake Level of 400 ug/day.
If some of the food eaten is very high in selenium and the cumulative intake gets to the 800 ug/d range, the result could be a nasty condition known as selenosis.
Minor symptoms include a garlic odor on the breath, GI disorders, hair loss, fatigue, irritability and neurological damage.
More serious outcomes could be cirrhosis of the liver, pulmonary edema or fluid accumulation in the lungs leading to respiratory failure, and death. A dose of as little as 5 mg (5000 ug) would be lethal for most humans.
In fact one source of Se overdosing has come from confusing mg with ug where taking a dose in mg when ug was intended would result in a tremendous overdose. This was what killed 21 polo ponies in 2009 following a match in the U.S. Polo Open.
Very small amounts are sometimes injected into the ponies to help them recover more quickly after the exertion of the match. In this case, a pharmacy made the fatal error of preparing the dosage which was 15 to 20 times higher than it should have been.
Disease prevention and Treatment
There is a lot of controversy when it comes of Se and certain diseases. There is enough evidence to show a linkage between certain cancers and selenium deficiency which, not surprisingly, triggered a considerable amount of interest.
One study showed that supplementation showed a reduced occurrence of various cancers including lung, colon and prostate accompanied by a significant reduction in cancer mortality. However it showed no effect on skin cancer which was the original focus of the study (JAMA 1997 May 21;277(19):1520).
Selenium is a Goldilocks situation; too much and you get toxic issues, too little and you risk deficiency problems. It seems that the Paleo Diet just might be the solution to getting just the right amount.
Studies show that 200 mcg/day is the optimum amount to achieve therapeutic effects for lung, colon and prostate cancers. It so happens that the Paleo Diet supplies just that amount. Not familiar with the Paleo Diet? Consider the book shown above.If you don't want to buy the book, at least go to Selenium Supplementation and the Paleo Diet for a quick introduction.
Studies directed at showing the cancer fighting properties of selenium due to its antioxidant capacity have not been in general agreement.
None of the studies were identical in construction and used differing combinations of supplements; some were heavy with smokers, others not; and results for males were not duplicated with females.
A review of all the studies concluded that there was no convincing evidence that adequately nourished people would benefit from supplementation with regard to cancer risk.
Yet there was solid evidence that selenium could improve the efficacy of chemo drugs, lower the body's resistance to the drugs and reduced the toxicity of chemo drugs on the patient.
AIDS patients have exhibited a strong correlation between low Se levels, decreased immune cell counts and increased disease progression.
Other research has shown that selenium supplementation along with other nutrients can prevent the recurrence of tuberculosis.
A couple of apparently contradictory studies showed that an excess of serum selenium levels was positively associated with type 2 diabetes while another more recent study indicated that it could inhibit type 2 diabetes in men.
The Bottom Line
In keeping with the "Healthy by Nature" theme of this website there is no better mineral than selenium to confirm that we must be smart about supplementing minerals.
Because a deficiency of Se is so rare in well nourished countries such as the U.S., supplementation of Se is not recommended unless special circumstances exist and then only under the care and direction of a qualified healthcare provider.