Spring 1997

Cornell Researcher Shows Selenium—Cancer Prevention Link
by Randi Rotjan

   A Cornell nutritional biochemist's work may do something to ease people's fears about cancer. In a double-blind, placebo-controlled cancer prevention study performed on humans, Professor Gerald Combs found evidence that directly supports the thesis that a nutritional supplement of selenium, as a single agent, can reduce the risk of many forms of cancer.

   Combs' work demonstrated that, over a ten year period, both men and women taking selenium supplements developed 41 percent less total cancer than those taking placebos. In January, the Journal of the American Medical Association published his research team's findings.

   Cornell engineering professors Bruce Turnbull and Elizabeth Slate took care of the study's statistical side while epidemiologist Larry Clark of the University of Arizona worked on the medical side. Combs, a nationally recognized authority on selenium, served as the team's selenium expert. He wrote the 1986 book The Role of Selenium in Nutrition, commonly referred to as a "bible of selenium."

Dr. Gerald Combs with liquid chromatograph in his Savage Hall lab. Photo by Adriana Rovers, courtesy of Cornell University Photography.

   According to Combs, researchers still have not entirely explained the function of selenium in the body. Scientists do, however, know that it proves essential in the creation of several enzymes with antioxidant-like functions and for the normal metabolism of the thyroid hormone. "It may have other functions, but each is likely to resemble these in that selenium serves as part of the active center of enzymes," Combs added.

   Selenium naturally gets into food products from the soil. The amount of selenium in food differs based on the soils in a given geographic region. While some areas of the United States—particularly the Northeast, Pacific Northwest and the Southeast—do have low-selenium soils, widespread shipment of food typically prevents selenium intake deficiencies in people in these geographic areas.

   In 1983, Clark suggested to Combs that they perform selenium research using patients with skin cancer, an easily diagnosable and treatable disease. Skin cancer patients made good research subjects because they have a 25 percent annual chance of cancer recurrence. The researchers set out to determine whether they could reduce the average recurrence rate with selenium supplements.

   The study began when researchers selected 1,312 patients with histories of skin cancer, all of whom lived in low-selenium soil areas of the U.S. and typically consumed 100 micrograms of selenium daily. Scientists and doctors observed the subjects for an average of seven years. The project itself lasted ten years because of study participants' staggered starts in the study. Twenty different physicians observed patients in seven different dermatology clinics.

   Medical personnel gave the participants either a placebo or a 200-microgram daily supplement of selenium. Researchers "blinded" the experiment on every level by preventing anybody taking part in the study from getting information as to who was taking the placebos.

   Though they originally set out to determine whether they could reduce the average recurrence rate of skin cancer with selenium supplements, the study's results were not statistically significant for changes in skin cancer recurrence rates.

   The results did, however, prove compelling for overall cancer rates. The study showed that the average recurrence rate was 35 percent less for lung cancer, 64 percent less for colerectal cancer, and 67 percent less for prostate cancer in patients treated with selenium supplements. Because 75 percent of the study's participants were male, Combs noted that the researchers could not form a strong hypothesis as to selenium's effect on breast cancer.

   The effects of the study's discoveries remain uncertain. If further research confirms these findings, it may lead to upward revisions in the Department of Agriculture's recommended daily allowance of selenium. Currently, the Department of Agriculture recommends 55 micrograms of selenium a day for non-pregnant adult women and 70 micrograms a day for adult men. Combs says that 200 micrograms daily of selenium—an amount many people already get—proves sufficient.

   Combs is confident that more developments will come from his work. "This is the first really solid evidence that increasing the intake of a single nutrient can reduce cancer risk—it is really exciting," he said.