Selenium
Selenium If you’ve heard anything about this essential trace mineral, it’s probably been news that’s related to cancer prevention. Studies from around the world suggest that where selenium intake is very low—usually because of selenium-poor soil—cancer rates tend to be higher than normal. "Selenium has been associated with reduced cancer risk since the late 1960s, but findings were slow to be popularized because of exaggerated concerns about the potential for toxicity," says Larry Clark, Ph.D., associate professor of epidemiology at the Arizona Cancer Center in Tucson. "Selenium actually has one of the strongest bodies of literature supporting its role as an anti-cancer agent. The data are overwhelming."
A study done by Dr. Clark and his colleagues hints at selenium’s potential. It was designed to look for a change in the rates of skin cancer and included more than 1,000 people (average age, 63) with a history of skin cancer.
The participants were divided into two groups and followed for six years. For about four years, one group received 200 micrograms daily of selenium from high-selenium yeast, which contains a special form of the mineral. The other group got inactive look-alike pills (placebos). When the study ended, the members of the group that had gotten the selenium had a 37 percent reduction in cancer risk. They also had a 50 percent reduction in cancer deaths.
Surprisingly, there was no reduction in the incidence of skin cancer. Instead, there were 63 percent fewer cases of prostate cancer, 58 percent fewer colon or rectal cancers, and 45 percent fewer lung cancers in the selenium group.
"It was a wonderful surprise," Dr. Clark says. "Not that we didn’t expect selenium to reduce cancer rates, but we didn’t expect it to have the power to produce such reductions in the short period of time of this trial."
Like vitamins SUPPLEMENT SNAPSHOT
| Selenium Supplement forms: Selenomethionine and sodium selenite. May help: Cancer, heart disease, angina, cataracts, hair loss, lupus, and HIV; may limit spread of chronic infections. Daily Value: 70 micrograms. Who’s at risk for deficiency: People who get most of their food from selenium-poor soil. Deficiency is rare in countries where food is transported or imported and where diets include meat and shellfish. Good food sources: Lobster, clams, crab, cooked oysters, and Brazil nuts. Cautions and possible side effects: Don’t take more than 200 micrograms in supplement form; higher amounts may cause fragile, thickened nails; stomach pain; diarrhea; loss of sensation in the hands and feet; fatigue; and irritability. Doses of about 800 micrograms have been known to cause tissue damage. |
Some research indicates that selenium may prevent cancer by inhibiting tumor growth and inducing a kind of suicide in malignant cells, Dr. Clark says. "In tumor cells grown in the laboratory, selenium stimulates programmed cell death, which is a very late effect in the cancer process. This makes us think that it is never too late to start taking selenium, because it may have effects on actual tumors as well as on premalignant cells."
Other selenium-dependent enzymes can disarm a veritable toxic-waste dump’s worth of harmful substances, including drugs, chemicals such as the herbicide paraquat, and toxic metals such as mercury, cadmium, and Arsenic.
Virus Fighter
Researchers first became interested in selenium’s role in viral infections when their attention was drawn to one area of China where the soil is low in selenium. People living in that low-selenium neighborhood were much more likely than normal to die of a form of heart disease called Keshan disease, which is characterized by cardiomyopathy, or weakening of the heart muscle. It is thought to be a result of a viral infection that occurs when a selenium deficiency causes a normally harmless virus to change into a deadly strain, Dr. Levander says.
Researchers know that in selenium-deficient animals, the harmless virus can mutate into a virulent form capable of causing heart damage and death. "In studies where the virus was removed from the selenium-deficient animals and injected into animals that were getting sufficient selenium, it remained in its deadly, mutated form," Dr. Levander says.
Several viruses are known to interact with selenium, according to Will Taylor, Ph.D., an AIDS researcher and associate professor at the College of Pharmacy at the University of Georgia in Athens. "The rate of progression from HIV to AIDS, for instance, has been strongly correlated with selenium status," he says.
In a study at the University of Miami, people with HIV who were deficient in selenium were 20 times more likely to die from AIDS within six months than people with normal selenium levels. Other viruses potentially linked with the mineral include hepatitis C and measles, Dr. Taylor says. No studies have been done on the effect of supplements, however.
Selenium apparently is used initially by viruses to help establish themselves in the body, so a viral infection can deplete the mineral. Later, however, during a long period when many chronic viral infections don’t create symptoms, selenium appears to act as a kind of viral birth control. It seems to restrict rather than encourage the spread of the virus.
How Much Is Enough?
The Daily Value for selenium is 70 micrograms, and people in the United States get an average of a little more than 100 micrograms of selenium a day. If you’re taking a selenium supplement, says Dr. Levander, you’ll want to use one that doesn’t put your total selenium for the day much above 350 micrograms (for a 154-pound person).
"We don’t have good information on when selenium becomes toxic, but taking no more than 200 micrograms a day as a supplement seems to be within reason for most people if they choose to supplement," he says.
