(CNN) -- Contrary to previous research, the supplement selenium does not reduce the risk of developing lung cancer, a new study shows.
From protecting against heart disease to combating cancer, selenium has been touted over the years. But a study by the MD Anderson Cancer Center found lung cancer patients taking the supplement did not reduce their risk of developing recurring lung cancer or a new cancer.
Over the last 10 years, researchers followed more than 1,500 Stage I non-small cell lung cancer patients that had had their tumors surgically removed and were cancer free for at least 6 months. Patients got 200 micrograms of selenium a day or a placebo.
The results were not encouraging.
"This process is very insidious and takes years," said Dr. Daniel Karp, the study's principal investigator and professor in the Department of Thoracic/Head and Neck Medical Oncology at MD Anderson. "And unfortunately we were not able to show that selenium produced any clear benefit."
Researchers started looking at selenium as a possible way to reduce lung cancer after a study in 1996 that examined the supplement and skin cancer development.
They found selenium didn't protect against skin cancer but did see about a 30 percent reduction in prostate and lung cancers. Large clinical trials began, but results have been largely negative. In fact, MD Anderson's lung cancer study was stopped early because an interim check found those taking the placebo were faring a bit better.
"What I can say with confidence is if you take someone with a resected stage I lung cancer and give them 200 milligrams of selenium a day for up to four years, there's no evidence that that's beneficial," Karp said. "In fact, it looks like people who took the placebo had fewer cancers."
In the study, 78 percent of patients taking the placebo had no recurrence of cancer after five years compared to 72 percent of those on selenium.
Dr. Mark Kris, chief of thoracic oncology service at Memorial Sloane Kettering Cancer Center, said his advice to consumers is to stop using selenium to prevent new or recurring cancers.
"One thing that has been shown to prevent second cancers is to stop smoking," he said. "In other trials like this, that is the common thread."
Karp agreed, saying that every patient in the study had a small lung cancer, and 80 to 90 percent of them were past or current smokers. The evidence, he said, supports the notion that tobacco carcinogenesis overwhelms mild supplements -- and that it might even be harmful.
"The message is for goodness sakes, stop smoking and if you can, make sure that young people don't start," Karp said.
Early detection is also key.
Lung cancer is the leading cause of death in the United States for both men and women, according to the American Cancer Society. There were nearly 220,000 new cases last year and 160,000 deaths.
When caught early, like Stage I, more than 80 percent of cases can be cured.