THURSDAY, Aug. 21 (HealthDay News) -- Older cancer survivors need to listen to warnings about the potential risks of dietary supplements, say Duke University Medical Center researchers and colleagues.

They noted that many older cancer patients who've survived five years or more take vitamins, minerals and other dietary supplements in an effort to remain disease-free. However, this supplement use may backfire.

"One of the most common behavioral changes cancer survivors make -- sometimes without a doctor's advice, often on their own -- is using dietary supplements in hopes of bolstering their health," researcher Denise Snyder, clinical trials manager at the Duke School of Nursing, said in a university news release. "Still, it's unclear whether supplements really help keep cancer survivors healthier or put them at further risk. They, like many other people today, use the Internet, and you can find a lot of false hope out there with supplements targeted at cancer survivors."

Snyder and colleagues at Pennsylvania State University and the University of Texas M.D. Anderson Cancer Center studied 753 cancer survivors, age 65 and older. About 75 percent of them were taking dietary supplements, including multivitamins (60 percent), calcium/vitamin D (37 percent), antioxidants (30 percent), and herbs, amino acids and glandular extracts.

"In our study, we see people taking supplements who have good diets and who are relatively healthy. While they may need a particular vitamin because they don't get enough of it, they may not need a multivitamin or supplement because of the increased risk of cancer recurrence or secondary cancer," Snyder said.

Before they start to take supplements, older cancer survivors should talk with their health care provider or a registered dietitian, she advised.

The study was published in the Journal of Cancer Survivorship.

More information

The American Cancer Society offers health advice for cancer survivors.