Many children with chronic medical conditions such as cancer and cystic fibrosis may be taking dietary supplements that are not part of their prescribed treatment, a new survey shows.

The study authors say this is worrisome, because the safety of many supplements -- particularly when taken along with standard medications -- is unclear.

The survey, given to parents of 505 chronically ill children, found that 62 percent of the children had taken vitamins, herbs, amino acids or other dietary supplements in the past year. Thirty percent had taken supplements that were not prescribed as part of their treatment, and in only a minority of these cases did parents tell their children's doctors about the supplement use.

"Few pediatric health care providers are aware of their patients' use of nonprescribed supplements," the study authors report in the Journal of the American Dietetic Association.

"This is a concern," they add, "because of the unknown effects of many supplements on growth and development and the potential for adverse drug interactions."

Parents or caregivers of chronically ill children "should discuss the use of unprescribed dietary supplements with their pediatrician, or a registered dietitian or pharmacist who has pediatric training," study co-author Dr. Laurie J. Moyer-Mileur stated.

Though health providers do not always know whether a supplement has the potential to interfere with medications or cause side effects, they do have access to such information, noted Moyer-Mileur, who directs the Center for Pediatric Nutrition Research at the University of Utah in Salt Lake City.

Overall, the study found that children with cystic fibrosis had the highest supplement use, often as part of their standard care. Cystic fibrosis is a genetic condition that causes respiratory difficulties and involves nutritional deficiencies, so children with the disease typically take vitamin and mineral supplements.

But cystic fibrosis patients in this survey were also among the most frequent users of nonprescribed supplements as well. Anywhere from 30 percent to 35 percent of children with cystic fibrosis, type 1 diabetes or neuro-behavioral disorders -- such as autism, Down syndrome and attention-deficit hyperactivity disorder -- were taking an unprescribed supplement.

Children with cancer, however, were most likely to take supplements that were not part of their prescribed care -- with 43 percent to 46 percent of parents reporting such use.

Overall, only 20 percent of the parents who gave their children unprescribed supplements had discussed it with their child's doctor. The large majority -- more than 78 percent -- cited books and magazines as their primary source of information on dietary supplements.

Though supplements may have health benefits, Moyer-Mileur and her colleagues note in their report, some have limited evidence that they work, or are even safe for children. In addition, a number of herbs -- such as St. John's wort and ginseng -- have been shown to interfere with the body's metabolism of certain medications, including some cancer drugs.

In the U.S., dietary supplements do not fall under the same government regulation that drugs do.

It's possible, Moyer-Mileur said, for a supplement to contain an amount of the active ingredient that is different from what's listed on the label, or to provide a dose that is appropriate for adults but not young children.

SOURCE: Journal of the American Dietetic Association, January 2005.