AACR.org - Supplementation with a mixture of antioxidants and the trace mineral selenium decreased the risk of developing new polyps of the large bowel - called colorectal metachronous adenomas - in people who previously had colorectal polyps removed.

“Our study is the first intervention trial specifically designed to evaluate the efficacy of the selenium-based antioxidant compound on the risk of developing metachronous adenomas,” said Luigina Bonelli, M.D., head of the unit of secondary prevention and screening at the National Institute for Cancer Research, in Genoa, Italy.

Adenomatous polyps (or adenoma) are benign lesions of the large bowel that, in time, could progress to cancer. Even though only a small proportion of adenomas will develop into cancer, almost 70 percent to 80 percent of colorectal cancer stems from an adenoma.

Adenomas are common in people aged 60 years or older; one in four people will have at least one adenoma.

Participants in this study were aged 25 to 75 years and had already had one or more colorectal adenomas removed, but did not have any other diagnosis of colorectal diseases, cancer or life-threatening illnesses and did not use vitamins or calcium supplements. The researchers randomized 411 participants to the placebo group or to receive an antioxidant compound - specifically selenomethionine 200 μg (micrograms), zinc 30 mg, vitamin A 6,000 IU, vitamin C 180 mg and vitamin E 30 mg.

“Our results indicated that individuals who consumed antioxidants had a 40 percent reduction in the incidence of metachronous adenomas of the large bowel,” Bonelli said. “It is noteworthy that the benefit observed after the conclusion of the trial persisted through 13 years of follow up.”

The researchers are currently conducting a study to evaluate the role of genetic alterations as predictors of metachronous adenomas in participants received the antioxidant compound compared with those in a placebo group.

Antioxidant study highlights:

• Five-year supplementation with selenium-based antioxidant mixture was beneficial for years.
• Supplementation reduced recurrence of colorectal adenomas by 40 percent.