Selenium, used as a nutritional supplement for decades with the belief it significantly lowered the risk of colorectal cancer, does not. Worse, in people with an adequate selenium intake, it more than doubles the risk of developing Type 2 diabetes.
Those were the conclusions reached by researchers at the University of Arizona Cancer Center, who conducted a 12-year study, Selenium Supplementation for Prevention of Colorectal Adenomas and Risk of Associated Type 2 Diabetes.” The study was published recently in the Journal of the National Cancer Institute.
Selenium, a popular nutritional supplement, has been thought to protect against the development of cancer. Indeed, studies have shown that selenium deficiency is associated with increased cancer risk, suggesting that its antioxidant properties and the ability to prevent free radicals from damaging cells and DNA play a key role in cancer prevention.
However, research also suggested that selenium could increase the risk of Type 2 diabetes.
To understand whether selenium truly could prevent colon cancer, researchers conducted a randomized, double-blind, Phase 3 clinical trial (NCT00078897) assessing the safety and effectiveness of selenium in preventing the recurrence of colon polyps.
The study enrolled 1,824 participants from clinical centers in Arizona, Colorado, Texas, and New York who were randomized to receive either selenium (200 µg daily in the form of selenized yeast), or placebo for three to five years, and then monitored for 12 years. Patients also received celecoxib (400 mg daily), a selective COX-2 inhibitor non-steroidal anti-inflammatory drug (NSAID), with or without selenium, but celecoxib was demonstrated to increase cardiovascular toxicity in patients with pre-existing cardiovascular factors.
Among 1,374 participants who took selenium or placebo and were available for analysis, results revealed that selenium did not change the risk for the development of colon polyps, the precursors of colorectal cancer, suggesting that, contrary to previous beliefs, selenium did not protect from colon cancer.
Importantly, the researchers found that selenium supplementation significantly increased the risk for Type 2 diabetes, more than doubling patients’ chances of developing the disease.
“Overall, selenium did not prevent colorectal adenomas and showed only modest benefit in patients with baseline advanced adenomas,” the researchers wrote. “With limited benefit and similar increases in T2D to other trials, selenium is not recommended for preventing colorectal adenomas in selenium-replete individuals.”
“The possibility that selenium supplements may increase the risk of Type 2 diabetes has been hinted at before,” Peter Lance, MD, deputy director of the UA Cancer Center and the study’s principal investigator, said in a press release. “But this is the first study to have substantiated such a risk in the setting of a prospective, randomized, placebo-controlled trial.”
Now, new studies are being conducted at the University of Arizona to unravel the molecular mechanisms through which selenium increases the chances of developing Type 2 diabetes.