"It's time to stop ignoring the facts?" say Richard A Passwater, PH.D., in his book, Selenium as Food & Medicine. "If you want to maintain your good health, increase your resistance to disease, and assure a long and energetic life, it is vitally important that you increase your intake of selenium." Selenium protects the membranes of each of our body's 60 trillion cells. The more selenium consumed the lower the incidence of cancer. . . . several physicians have found that when sufficient selenium is ingested by cancer patients to raise their blood levels of selenium to the desired range, their tumors began to shrink"

Dr. Gerhard Schrauzer of the University of California says: "If every woman in America started taking selenium today, or had a high-selenium diet, within a few years the breast cancer rate in this country would drastically decline." Dr. Raymond Shamberger of the Cleveland Clinic Foundation advises people to increase their intake of selenium to 200 micrograms a day, because "it can reduce the cancer rate dramatically for some type of cancers, particularly cancer of the colon, breast, esophagus, tongue, stomach, intestine, rectum, and bladder."


People are increasingly turning to supplements as a way to fend off cancer. In fact, specific nutrients seem to jockey for position in the cancer-prevention game like children playing musical chairs. One of the prominent players right now is the mineral selenium.

Selenium was once one of the least celebrated nutrients, because deficiencies were rare in the U.S., while toxicity was a risk. Those facts haven't changed, but perceptions have. Nutritionists now also consider prevention of chronic diseases like cancer (rather than just considering prevention of deficiencies) when determining the optimal intake of a nutrient. Concern over the toxicity of selenium is now viewed as a manageable risk by some.

But can selenium live up to its new celebrity status? Is it destined to become the next need-to-have nutrient or have its cancer prevention possibilities been overstated?

"At the present time," says Blossom Patterson, Ph.D., of the National Cancer Institute, "selenium is one of the most promising nutrients in cancer prevention research." That's high praise coming from a government organization. But Patterson emphasizes the word promising when discussing the results of recent research on selenium and cancer, citing the need for larger and better studies.

Patterson's wait-and-see attitude about selenium is shared by many nutrition researchers who are optimistic about its role in cancer prevention, but are realistic about what has yet to be proved. Here's a look at where the science now stands.

The first hint of selenium's possible role in cancer prevention came from animals 30 years ago. Several population studies since then have also documented a link. Much of the subsequent research on selenium as a cancer preventer has been in laboratory animals given high doses of selenium. Results have been mixed, though in hindsight this may have been due to differences in the forms of selenium used. (See box.)

The research that generated the most headlines and brought serious notice to selenium was a well-controlled 1996 study that looked at the effect of 200-microgram-a-day doses of selenium (as high-selenium yeast) on the occurrence of skin cancer in 1,400 people over four years. (See EN, March 1997.)

Though the selenium had no apparent effect on skin cancer, the researchers were surprised to discover that the people taking selenium had much lower rates of prostate, colon and lung cancers than those who got placebos--so much so, that the study was halted early for ethical reasons. Because the research targeted only people with skin cancer and low selenium intakes, however, it's premature to assume the results apply to everyone, says Gerald F. Combs, Jr., Ph.D., of Cornell University, one of the researchers. The findings need to be replicated in a general population.
How Selenium Might Work. As an essential component of an antioxidant enzyme, selenium has traditionally been viewed as a potent antioxidant, working in concert with vitamin E. Research suggests that antioxidants help lower cancer risk by preventing cell-damaging free radicals from forming. Yet selenium's most powerful anticancer effects may lie in other processes.

Apoptosis is biology's term for cell suicide. Researchers think it's one way people are able to fight off constant cancer threats. The body literally induces cancer cells to self-destruct. Cancer can develop, however, if apoptosis is suppressed, perhaps by genetics gone awry, dietary factors or environmental insults. Conversely, certain substances may bolster apoptosis of cancer cells. Selenium is one such substance.

Alternatively, some researchers (including Combs) believe antitumor substances in cells might somehow be activated by selenium. Or the mineral may simply boost immune function.

Safety First. The medical literature yields more information on selenium toxicity than on the mineral's cancer-fighting potential. And for good reason. Selenium is known to be toxic at levels of more than 800 micrograms a day.
Marco Polo reportedly was one of the first to notice selenium poisoning during his famed trip to China. After feeding on selenium-rich plants, his horses became so ill the hooves of those most severely affected literally fell off.
Similar effects--nail and hair loss-are seen in people suffering selenium toxicity. Other symptoms include nausea, fatigue and nerve damage, warns Karen Collins, M.S., R.D., of the American Institute for Cancer Research.

The Recommended Dietary Allowance (RDA) for selenium is 70 micrograms a day for men and 55 for women. This is above and beyond what will prevent a deficiency, but probably isn't enough for disease prevention.

"While most Americans get enough selenium from their diets to meet the RDA," Combs points out, "selenium's cancer-prevention properties probably don't take effect until more than 150 to 200 micrograms a day are consumed." Certainly, if you take a selenium supplement, it shouldn't exceed those levels, since diet and a multi-supplement add even more to the daily total, risking toxicity if you're not careful. Even Combs doesn't recommend a selenium supplement until more is known.

"I advise people to eat plenty of grains, beans and lean meats," he says, "and perhaps include a daily multivitamin that contains selenium."

Bottom Line. EN echos that advice and advises consumers to hold off on selenium supplements for now and, instead, concentrate on reducing cancer risk by adopting other health habits with a more proven track record, such as:
Eat five or more servings of fruits and vegetables every day.
Eat whole-grain foods.
Stop smoking.
Selenium Superstars
Food Selenium

Brazil nuts (sold unshelled), 436
1/2 ounce (4 medium nuts)[*]
Tuna, light, 31/2 ounces 80[a]
Flounder, 3 1/2 ounces 58[a]
Pork, sirloin, 3 1/2 ounces 52
Clams, canned, 3 1/2 ounces 49[a]
Turkey, dark meat, 3 1/2 ounces 41
Turkey, white meat, 3 1/2 ounces 31
Pasta, cooked, 1 cup 30
Pita bread, whole wheat, 1 (6 1/2-inch) 29
Special K, 1 1/2 cups 28
Bagel, 1 (3 1/2-inch) 23
Sunflower seeds, 1 ounce 22
Granola, 1 1/4 cups 21
Cheerios, 1 1/2 cup 19
English muffin, 1 15
Tofu, 1/2 cup 11
Bread, whole wheat, 1 slice 9
Pinto beans, boiled, 1/2 cup 6
Navy beans, boiled, 1/2 cup 3
* Brazil nuts sold in the shell have significantly more selenium than Brazil nuts sold shelled.
a Only 20% is thought to be usable by the body. Sources: USDA; Bowes & Church's Food Values of Portions Commonly Used (Lippincott, 1998).
By Luanne Hughes, M.S., R.D.
Adapted by M.S., R.D.

Researchers advise against selenium supplements until they can confirm anticancer benefits and pinpoint the amount that optimizes benefits while not risking toxicity. Most, however, believe 200 micrograms a day is probably safe.
The form of selenium might make a difference. The 1996 research (see article) used high-selenium yeast (brand name Selenomax from Nutrition 21). A large trial in China using the same type of selenium also found protection against cancer, while inorganic selenium offered no protection. Most supplements on the market, including multivitamin/mineral supplements, use inorganic forms of selenium (sodium selenite or selenate). Other high-selenium yeast supplements are sold, but they may simply be yeast sprayed with inorganic sodium selenite.

Anyone considering a selenium supplement needs to be sure that total intake, including diet and other supplements, does not exceed 800 micrograms a day.


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A multi-national, double-blind cancer prevention trial commenced in December with the recruitment of participants in Denmark. The trial, expected to include 52,500 participants in six countries, is in response to recent editorials in several leading medical journals calling for definitive tests of the hypothesis that supplementation with selenium can prevent different types of cancer in humans.

Dr. Larry C. Clark of the University of Arizona Cancer Center is directing the project, known as PRECISE (Prevention of Cancer with Selenium in Europe and America). Dr. Clark's earlier cancer prevention trial in the United States produced a 37 percent reduction in the incidence of cancer and 50 percent reduction in cancer mortality in individuals receiving a selenium supplement. He served as principal investigator on the 10-year study, beginning in 1983, that suggested selenium supplementation may significantly lower the incidence of prostate, colorectal and lung cancers in people with a history of skin cancer. Three quarters of the 1,313 patients were men. This new study is intended to confirm that selenium supplementation can reduce cancer incidence in the general population.

Selenium is an essential micronutrient in the human functioning as a component of enzymes involved in antioxidant protection (thus its potential as a cancer deterrent) and thyroid hormone metabolism. Selenium works with vitamin E to exert antioxidant effects that help keep the immune system strong.

In addition to its potential as a cancer deterrent and immune system cancer deterrent and immune system booster, some studies suggest that selenium may prove effective for the treatment of psoriasis, arthritis and macular degeneration.

Important food sources of selenium include meats, fish and grains. The amount of selenium in food depends partly on where it is grown. The soil of the western United States has a concentration of selenium high enough that people who eat products grown there probably get enough of the mineral from their diets.
Source: Council for Responsible Nutrition News, January/February 1999.