Selenium Seen as Prostate Protector
Breast cancer has drawn more publicity and advocacy efforts, but prostate cancer kills an equal number of Americans - 40,000 - every year. Now, newly published research (Journal of the National Cancer Institute, August 1998) indicates that the essential trace mineral selenium is a powerful preventive factor. Harvard University researchers conducted the seven-year study of 33,737 male health professionals, which found an association between higher selenium levels and reduced risk of advanced prostate cancer. After accounting for all other influencing factors (age, weight, vasectomies, diabetes, smoking, and family history), the researchers concluded that men with the highest levels of selenium in their bodies had only one-third the risk of developing advanced prostate cancer.
It's not clear exactly how selenium wards off cancer. Selenium is an essential component of the enzyme glutathione peroxidase, one of the body's key antioxidants, which can inhibit cancers. Selenium also may stimulate programmed cell death in cancerous cells. In any case, selenium's cancer-inhibiting powers extend well beyond the prostate gland:
In 1996, University of Arizona researchers reported that patients who took daily selenium supplements had 63 percent fewer cases of prostate cancer, 58 percent fewer colon or rectal cancers, and 45 percent fewer lung cancers than those not receiving the supplement. Skin cancer patients in a 1997 American study had 37 percent fewer malignancies, a 50 percent reduced risk of death from cancer, and a 17 percent decrease in overall mortality, when given 200 micrograms of selenium per day. It is believed that selenium supplementation works at its highest potential in the early stages of cancer development.
Low soil levels of selenium are associated with higher cancer rates, and soil-rich areas have below-average cancer rates for a number of body systems, particularly the breasts, colon and lungs. Keshan disease, a form of heart disease prevalent in children and characterized by an enlarged heart and congestive heart failure, may be a direct result of selenium deficiency; it has responded well to selenium treatment. People in Keshan, China, where the disease was discovered, treat it with a common herb called astragalus, which accumulates selenium from the soil.
As in the Keshan area of China, the soil in many parts of the United States is very low in this important mineral. Western states generally have higher selenium levels than the eastern; South Dakota has the highest and Ohio the lowest. Ohio has more than twice South Dakota's rate of a number of common cancers. Most states with high levels of soil selenium show a decreased rate of cancer deaths.
Dietary sources of selenium include meat, fish, whole grains, dairy products and vegetables grown in selenium-rich soil. Supplemental selenium is available in two forms. The organic form, selenomethionine, which is usually extracted from yeast or ocean plants, is more easily absorbed and raises selenium levels in the blood. The inorganic form, sodium selenite, is more effective at increasing activity of the antioxidant enzyme glutathione peroxidase.
Too much selenium can cause baldness, tooth loss and fatigue. Toxic effects begin to appear in people consuming more than 750 micrograms per day. The prostate cancer study participants consumed 86 to 159 micrograms per day, all from foods. Participants in the Arizona study were given daily supplements of 200 micrograms, with no reported ill effects. The current recommended daily allowance of selenium for men is 70 micrograms-an amount that appears inadequate for cancer prevention.
