NEW YORK (Reuters Health) - Having one or more chronic illness is the primary factor associated with the use of dietary supplements. Cancer survivors also use supplements to treat chronic medical conditions, but not specifically for cancer, a new study shows.

Given the lack of information on the risks and benefits of many supplements, as well as their potential for interaction with drugs cancer survivors may be taking, such as tamoxifen, it's imperative for cancer patients to let their physician know about what non-prescription medications and natural products they may be taking, lead author, Dr. Melissa Farmer Miller, told Reuters Health.

"We really are just beginning to build an evidence base on the benefits of dietary supplements," said Miller, of the National Cancer Institute in Bethesda, Maryland. "Even if there's not a benefit, there is a potential for them to cause harm."

Supplement use is growing among all Americans, Miller noted. To understand whether cancer survivors are using supplements more than the general population, she and her colleagues analyzed information from 1,844 cancer survivors and a random sampling of 7,343 people with no history of cancer.

The only type of supplement use independently associated with having a cancer diagnosis were single vitamins, the

researchers found. However, the subjects who reported having a chronic illness were 82 percent more likely than those without a chronic disease to be using two or more supplements, whether or not they also had cancer.

Other factors associated with the use of dietary supplements included female sex, older age, greater physical activity, consumption of fruits and vegetables, and the use of other complementary and alternative medicines.

Miller noted that it's impossible right now to definitively state that people living with cancer should -- or shouldn't -- take supplements. "The primary message should always be to promote a healthy diet," she said.

Doctors and other health professionals caring for cancer patients should be up on the literature about various supplements and should be sure to ask about supplement use, Miller said.

Cancer patients also need to be as well informed as possible about any supplement before they take it, Miller said. This can be tough, she noted, given the lack of regulation of dietary supplements in the U.S. and the limited information on their risks and benefits.

"Consumers are really kind of out there on their own, and should confer with their health care providers about supplement use."

SOURCE: Journal of the American Dietetic Association, March 2008.