Some epidemiological and animal studies have suggested a link between a deficiency in the dietary mineral selenium and cancer development. A ten-year Phase III clinical trial conducted at the Texas MD Anderson Cancer Center has found no benefit to taking the supplement, and in fact is halting the study because those taking a placebo appear to be living longer.
More than 1500 stage 1 non-small cell lung cancer patients who had survived their initial bout with the disease were studied between 200 and 2009. All had undergone surgery to remove their tumors and remained cancer-free for a minimum of six moths post-treatment. Half of the patients were placed on a regimen of 200 micrograms of selenium, while the other half took a placebo.
Selenium is a trace mineral essential to health but required only in small amounts (55 micrograms per day for most adults). The antioxidant properties are thought to help prevent cellular damage from free radicals that may contribute to the development of cancer. Foods rich in selenium include Brazil nuts, tuna canned in oil, beef, turkey, and grains such as rice.
The researchers found that selenium offered no protection against recurrence or onset of a new cancer or second primary cancer.
The study was halted when the team found that those in the placebo group had better survival rates five years later than those taking the supplement. While 78% taking the placebo survived over that time period, the rate was just 72% of the selenium group. Additionally, 1.4% of the placebo group developed a second primary tumor within a year compared to 1.9% of the selenium group.
Lead author Dr. Daniel D. Karp, professor in the department of thoracic/head and neck medical oncology, will present the findings today at the American Society of Clinical Oncology annual meeting in Chicago.
Dietary supplements have long been studied in the prevention of cancer with mixed results. A 1996 study found that selenium intake was associated with a 30% reduction in prostate and lung cancers. However, in 2009, a National Cancer Institute study called SELECT was halted because selenium and vitamin C were not found to reduce the risk of prostate cancer in men.
Lung cancer is the leading cause of death in the United States for both men and women, according to data from the American Cancer Society. When caught early, and the tumor is surgically removed, more than 80% of cases can be cured.