Past research on selenium and colorectal cancer has yielded mixed results, with some experts reporting a drop in colon cancer risk with selenium and others finding no selenium advantage.
Those studies may have been too small to track the mineral's impact, say researchers including Elizabeth Jacobs, PhD, of the Arizona Cancer Center at the University of Arizona.
To fix that problem, Jacobs and colleagues analyzed data from more than 1,700 people who had participated in three earlier colorectal cancer trials.
Each trial focused on preventing colorectal adenomas -- cancerous outgrowths or polyps in the colon or rectum. Participants had already had one adenoma removed during colonoscopy and were trying different nutritional approaches to avoid a recurrence of the cancerous polyps.
One trial tested a high-fiber cereal supplement. Another used a low-fat, high-fiber diet with many fruits and vegetables. The third study involved vitamin C, E, and beta-carotene supplements. The main dietary sources of selenium in the U.S. are grains.
Taking all three trials into consideration, Jacobs and colleagues found that participants with the highest blood levels of selenium were 34% less likely to develop a new adenoma compared with those with the lowest selenium blood levels.
The results support previous findings that "higher selenium status may be related to decreased risk of colorectal cancer," write the researchers in the Nov. 17 issue of the Journal of the National Cancer Institute.
However, that's not necessarily a reason to stock up on selenium supplements.
None of the participants in the studies took selenium supplements, notes a Journal of the National Cancer Institute editorial by experts including Anna Duffield-Lillico of Memorial Sloan-Kettering Cancer Center in New York City.
A Little Selenium Goes a Long Way
People only need a tiny amount of selenium -- 55 micrograms per day for adults, according to the U.S. Recommended Daily Allowance.
It's easy to get that amount from a healthy diet. Meats, seafood, grains, and some nuts (such as Brazil nuts) are good sources of selenium. Foods grown in areas with selenium-rich soils have higher levels of the mineral, but selenium deficiency is rare in the U.S.
Expect more news in the future on selenium and colon cancer. More than 35,000 men are currently taking part in a cancer prevention trial that will include an assessment of selenium and colorectal cancer, note Duffield-Lillico and colleagues.