Selenium was discovered in 1817 and named after Selene, the Greek Goddess of the Moon. This element is a member of the Group 16 (VIA) family of elements in the periodic table, along with oxygen, its sister sulfur, and the metalloid elements tellurium and polonium. Soil contains selenium in minute and variable amounts. In the U.S., soil selenium concentration ranges from <.05 to >50 parts per million (ppm). In the Pacific Northwest, Great Lakes region, Northeast, and Florida, where the soil comes from volcanic or washed coastal deposits, soil selenium concentration is low (<.05 ppm). In the Midwest, with its soil derived from cretaceous shales, soil selenium concentrations are 40 to 200 times higher (2 to 10 ppm), and in some areas, greater than 50 ppm. The concentration of selenium in the earth’s crust is less than that of gold.
Plants take up selenium from the soil and propagate it through the food chain. Brazil nuts, in particular, like selenium. One unshelled Brazil nut (one you have to crack open yourself) contains an average of 100 micrograms (mcg) of selenium per nut. (Already shelled Brazil nuts have 12 to 25 mcg of selenium per nut.) Phytoplankton, the "plants of the sea," extract and concentrate the even more minute amounts of selenium in ocean water and provide this needed element to fish. Selenium was identified as an essential trace element for mammals in 1957, and investigators now have determined that the cells of all organisms, bacterial, animal, and non-animal, need selenium.
Two amino acids, among the 20 that the body uses to make proteins, contain sulfur — methionine and cysteine. Selenium has similar chemistry and replaces the sulfur atom in these amino acids. Selenocysteine, selenium bound to cysteine, a "21st" amino acid, is the active site in some 35 proteins. Several are enzymes. Glutathione peroxidase, with four selenium atoms, is a powerful antioxidant (it reduces hydrogen peroxide to water and oxygen and lipid hydroperoxides to alcohol). Iodothyronine deiodinase converts the thyroid hormone T4 (thyroxine) into its active form T3 (triiodothyronine). Since this enzyme requires selenium to function properly a deficiency of selenium can cause hypothyroidism. Thioredoxin reductase regenerates antioxidant systems and regulates gene expression. All living things contain this selenium-dependent enzyme (Protein Sci 2003;12:372—378).
The proteins that selenium seed have antioxidant, anti-inflammatory, and immune enhancing properties that altogether foster a long, healthy life, akin to what Selene sought for Endymion (if in sleep) in Greek mythology. Selenium blood levels tend to fall as people age. In one study, investigators followed 1,300 people age 60—71 years for 9 years and found that those with the greatest decrease in blood selenium had the highest likelihood of cognitive decline. The same study showed that people with a low selenium blood level also had a shorter life span.
Cancer cuts short many lives. One in three Americans will have some kind of cancer during their lifetime. The Center for Disease Control and Prevention (CDC) reports that in 2004 (the most recent data available) cancer was the cause of death in 550,000 Americans, many of them in the prime of life.
A growing body of evidence indicates that selenium can prevent cancer. Studies show that low selenium blood levels are associated with an increased risk of cancer. One done in Finland showed that people with low selenium bloods levels are much more likely to develop lung cancer, especially if they smoke, than smokers and nonsmokers with high selenium levels. Another one, the Harvard Health Professionals Cohort study in 34,000 men, found that men with the lowest selenium levels had three times the likelihood of developing advanced prostate cancer compared with those who had the highest levels. These and other epidemiological, cohort, and case control studies suggest that selenium plays a role in cancer prevention. Now, however, there is strong scientific evidence that selenium does indeed reduce the risk of cancer. Evidence from a well-conducted randomized, placebo-controlled, double-blind trial proves beyond a reasonable doubt that this is the case.
The Nutritional Prevention of Cancer (NPC) trial recruited 1300 patients with nonmelanoma skin cancer who were randomized to receive 200 mcg of selenium a day or a placebo for a mean 4 years. Selenium decreased the overall incidence of all cancers by 35% and cancer mortality by 50%. Prostrate cancer decreased by 63%; colorectal cancer, by 58%; and the incidence of lung cancer decreased by 46%. All of these decreases in cancer incidence and mortality are statistically significant (JAMA 1996; 276:1957—1963). Seven other clinical trials on the effects of selenium supplementation on the incidence of cancer, done in China (5), India (1), and Italy (1) with varying degrees of randomization, support the NPC findings (Brit J Nutr 2004;91:11—28).
Antioxidant protection and enhanced immune surveillance are two mechanisms researchers have proposed to account for selenium’s anticancer effect. Others include enhancement of apoptosis (programmed cell death), regulation of cell proliferation, suppression of angiogenesis (growth of blood vessels supplying nutrients to the cancer), and inhibition of tumor cell invasion. Studies on cells in tissue cultures and in small animals indicate that two metabolites of selenium, hydrogen selenide and methylselenol, play a central role in cancer prevention and suppression (Zeng. J Nutr Biochem 2007; Epub ahead of print June 27). In order for enough of these metabolites to form and exert their anticancer effects, "supranutritional" doses of selenium have to be given. An equivalent dose for humans is 200—400 mcg/day of selenium.
In 2000, the U.S. Food and Nutrition Board (in the Institute of Medicine) revised the Recommended Dietary Allowance (RDA) for selenium, setting it at 55 mcg per day (it had been 70 mcg/day for men and 55 mcg/day for women). This is the "nutritional" dose, said to be adequate for 98 percent of the population. It is based on two studies that show this amount of selenium supports the maximal expression of glutathione peroxidase, which is regarded as fully discharging the nutritional effects of this element. A supranutritional dose is one that is 5 to 10 times higher than the RDA and not toxic. The government-funded experts who set the RDA for selenium did not take into account the NPC trial results, reported in 1996, four years earlier, that shows that a dose four times higher (200 mcg) has an anticancer effect.
The U.S. Food and Nutrition Board set the tolerable upper intake level (UL) for selenium at 400 mcg/day. Chinese authorities place the UL, which they term "no adverse effect level," at 819 mcg/day and the "low adverse effect level" at 1540 mcg/day. China is unique in having areas where the soil selenium level is severely deficient and other areas where the levels are toxic. The first indication of selenium toxicity is "garlic breath" and dry skin. Then the fingernails develop white patches, become brittle, and fall off. In studying the health effect of various levels of dietary selenium intakes in China, investigators found that hair and nail loss occurs when selenium intake reaches 4,990 mcg/day (J Trace Elem Electrolytes Health Dis 1994;8:159—165). These findings indicate that consuming 200—400 mcg of selenium a day to keep cancers from occurring will be well tolerated, without side effects, on top of one’s dietary intake of selenium, which in the U.S. ranges from 60—110 mcg/day (in Europe it is 11—67 mcg/day).
A recently published study in the Annals of Internal Medicine, which does not like supplements, warns that selenium u201Cmayu201D increase the risk for type 2 diabetes. This study is badly flawed. One of its major defects, among others, is that the investigators did not do any blood tests for diabetes at the start of the trial (where subjects were randomized to take selenium or a placebo) and relied simply on what the study subjects told them. Only 4% said that they had diabetes, whereas the true prevalence of diabetes in people their age, >60 years old, is 16.0% in men and 14.4% in women; and undiagnosed diabetes is present in an additional 7.9% of men and 4.2% women (Diabetes Care 2006;29(6):1263—1268). This study is not credible and is no cause for alarm. People with diabetes can take selenium without being concerned that it might make their diabetes worse.
The Moon Goddess’ element has other beneficial effects on human health. The heart does not function well without selenium. People in the Keshan province of China, where selenium content in the soil is very low, develop a severe form of heart failure, a dilated cardiomyopathy known as Keshan’s disease. Selenium supplements reverse it. Heart failure can occur after weight loss (bariatric) surgery due to selenium deficiency resulting from malabsorption, which resolves when selenium is administered intravenously (J Trace Elements Med Biol 2004;18:81—88). And researchers have shown that selenium helps the heart recover after it is temporarily deprived of oxygen, something surgeons do in performing heart surgery.
Selenium may help prevent coronary artery disease (atherosclerosis). It is biologically plausible because oxidation of low-density lipoprotein (LDL) is an initiating event in the inflammatory process that produces atherosclerotic coronary plaques, and the antioxidant selenium enzymes glutathione perioxidase and thioredoxin reductase can prevent LDL from becoming oxidized. This postulation awaits study.
Selenium stimulates the immune system and has been shown to be effective in treating sepsis (blood stream infection). Studies show that it increases the number of T cells circulating through the body, both CD4 helper T cells and CD8 cytotoxic (killer) T cells. Even given a good dietary intake (120—134 mcg/day), selenium supplementation still has considerable immunoenhancing effects. At Harborview Medical Center, the noted trauma and burn center at the University of Washington, patients in the intensive care unit receive 400 mcg/day of selenium intravenously for 2 days and then 400 mcg/day by mouth (or through a feeding tube) for the next 5 days (along with 1,000 mg of vitamin C and 1,500 IU of vitamin E).
Selenium also affects male fertility. It is required for synthesis of testosterone and to keep sperm structurally intact. Experts in animal husbandry recognize that selenium is essential for successful reproduction. In the U.S., soil scientists reckon that selenium deficiency is a major problem for livestock and wildlife in at least 37 states.
The Goddess of the Moon looks fondly at life on Earth; and she provides an element, rarer than gold, to sustain it. We cancer-prone humans need more selenium than most of us get in our diet. An additional 200 mcg/day of selenium, as selenomethionine or in an inorganic form, is well tolerated and has no side effects. It will help us enjoy optimal health, and live a long life cancer-free and mentally intact.