Could Dietary Supplements Increase Your Risk of Cancer?

While many Americans look to over-the-counter dietary supplements to improve their general health, they may actually be increasing their cancer risk if they exceed the recommended dietary amount, according to research presented earlier this week at the American Association for Cancer Research Annual Meeting in Philadelphia.

Researcher Tim Byers, MD, MPH, discussed these findings as part of a forum that presented the most up-to-date research on the benefits and risks of dietary supplements in cancer risk and prognosis.
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“We have not yet identified any supplements as effective (for cancer prevention), but we have found some to increase cancer risk, including folic acid, beta carotene, and vitamin E,” said Byers, associate director for cancer prevention and control at the University of Colorado Cancer Center. “The take-home message should be concern about safety of all the unregulated usage of nutritional supplements.”

During the presentation, he reviewed 30 years of human trials testing vitamin and mineral supplements for cancer prevention. For a decade, Byers and his colleagues studied thousands of patients who were taking dietary supplements and placebos. They initially hypothesized that taking extra vitamins and minerals would further reduce cancer risk—but they found quite the opposite.

“We found that the supplements were actually not beneficial for their health,” he said. “In fact, some people actually got more cancer while on the vitamins.”

One trial that explored the effects of beta-carotene supplements showed that taking more than the recommended dosage increased the risk for developing both lung cancer and heart disease by 20%. Another found that folic acid—which was thought to help reduce the number of polyps in a colon—actually increased the number in the patients they studied.

Byers emphasized that patients don’t need to be afraid of taking vitamins and minerals, but that many adults who take dietary supplements may not need them. He said patients can get the daily recommended doses of vitamins and minerals in their diets by eating healthy.

“Multivitamins that contain recommended dietary amount levels seem safe but, frankly, I think providers should advise against supplement use unless a patient has particular nutrition or dietetic problems,” Byers said.

—Colleen Mullarkey

Reference

Byers T. Dietary supplements and cancer risk and prognosis. Presented at the American Association for Cancer Research Annual Meeting 2015, Philadelphia, Pa. April 20, 2015.