Selenium May Reduce Cancer Risk, Study Says
Serving up preliminary yet provocative new evidence that a mere nutrient pill may help prevent some cancers, a study of more than 1,300 people found that those who took a daily supplement of the mineral selenium cut their overall cancer risk by nearly 40% compared to those who took a dummy pill.
Specifically, the group taking the selenium had 46% less lung cancer, 58% less colon or rectal cancer, and 63% less prostate cancer than the others after about five years. Moreover, when people on selenium did get cancer, they were 50% more likely to survive it than the others who were afflicted.
The new research, published today in the Journal of the American Medical Assn., is the first scientifically controlled clinical trial that directly tests a selenium supplement’s anti-cancer effects in people. It adds to the growing--yet often contradictory--body of research suggesting that consuming higher than usual amounts of a particular nutrient, such as vitamin E or beta carotene, can affect one’s cancer risk.
The findings were so dramatic that even the study’s lead author tempered his excitement with caution, lest the news start a selenium stampede. The study “opens a new era in cancer research prevention,” said Larry Clark, an epidemiologist and longtime selenium researcher at the Arizona Cancer Center in Tucson.
But, he said, the findings are too preliminary to justify widespread use of supplements. “This is not a cure for cancer. This is not a treatment for cancer. We’re not recommending that people start taking selenium.”
“It’s one study with provocative findings that have to be confirmed,” said Dr. Peter Greenwald, director of cancer prevention and control at the National Cancer Institute, which partially funded the research. “We do not recommend supplements” to prevent cancer, he said.
Selenium is classified as a “trace element” or “micronutrient” because the body requires so little of it to function. Outright selenium deficiency disease is virtually unheard of in the United States, public health experts say, but it has broken out in China, leading to excess heart disease. The U.S. government’s daily recommended dietary allowance is 70 micrograms for men, 55 for women. These levels are usually met in diets rich in nuts, grains, eggs, meat and fish.
For decades, researchers have puzzled over selenium’s role, if any, in cancer. Population studies show that cancer rates tend to be higher where soil has scant selenium, and numerous lab studies have found that animals exposed to cancer-causing substances develop fewer tumors if they are given large amounts of selenium.
However, other studies have detected no correlation between human blood selenium levels and cancer risk, and some have suggested that the higher the selenium intake, the higher the cancer risk.
Clark and his co-workers originally set up the new study, which started in 1983 at seven dermatology clinics nationwide, to test whether people who once had skin cancer could prevent a recurrence by taking selenium supplements. The 200-microgram, yeast-derived selenium pills came from Nutrition 21, a San Diego mineral supplier, which partially funded the research.
As it turned out, the scientists observed no difference in skin cancer recurrence between the 653 people in the supplement group and the 659 controls. But they did find “unanticipated” differences for other cancers.
While 31 people in the control group developed lung cancer (4.7%), 17 did in the supplement group (2.6%); 35 controls (5.3%) developed prostate cancer, versus 13 on selenium (2%); and 19 controls got colon or rectal cancer (2.9%), versus eight on selenium (1.2%).
Too few women were studied to determine whether the supplement affected breast or ovarian cancer rates, the researchers said.
Skeptics highlighted what they called the study’s shortcomings. Because the subjects were not randomly drawn from the population as a whole, it is not clear that the findings apply to everyone, they said. And because it was primarily designed to study people with skin cancer, it is possible that the other tumors appeared disproportionately in the control group by chance.
Greenwald said that additional studies, involving many more people, are needed to verify selenium’s effect. Meanwhile, he urged consumers to reduce their cancer risk by quitting smoking, boosting intake of fruits, vegetables and whole grains, and cutting down on fat.
While some researchers expressed doubts that a nutrient pill could produce such dramatic results in just four or five years, Clark said it was misleading to focus narrowly on the numbers rather than the general--and rather hopeful--trend.
“What’s important to come away with is not the size of the reduction” in cancer risk in the supplement group, “but the fact that there was a significant reduction in risk. I would hang my hat on the fact that future studies will replicate a reduction risk.”
Over-the-counter sales of selenium supplements have been growing 15% annually, to about $5 million last year, said supplement maker Leiner Health Products. Researchers caution that there are hazards in taking too much selenium: Symptoms of chronic selenium excess include garlicky breath, baldness, loss of nails and teeth, fatigue and occasionally death.
In an AMA journal editorial commenting on the new study, Harvard University epidemiologist Graham Colditz said: “It is premature to change individual behavior, to market specific selenium supplements, or to modify public health recommendations based on the results of this one randomized trial.”
