Excessive use of dietary supplements linked to increase cancer risk

"We are not sure why this is happening at the molecular level but evidence shows that people who take more dietary supplements than needed tend to have a higher risk of developing cancer," explains Byers, associate director for cancer prevention and control at the CU Cancer Center.

The line of research started 20 years ago with the observation that people who ate more fruits and vegetables tended to have less cancer. Researchers including Byers wanted to see if taking extra vitamins and minerals would reduce cancer risk even further.

"When we first tested dietary supplements in animal models we found that the results were promising," says Byers. "Eventually we were able to move on to the human populations. We studied thousands of patients for ten years who were taking dietary supplements and placebos."

The results were not what they expected.

"We found that the supplements were actually not beneficial for their health. In fact, some people actually got more cancer while on the vitamins," explains Byers.

One trial exploring 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 percent. Folic acid, which was thought to help reduce the number of polyps in a colon, actually increased the number in another trial.

"This is not to say that people need to be afraid of taking vitamins and minerals," says Byers. "If taken at the correct dosage, multivitamins can be good for you. But there is no substitute for good, nutritional food."

Byers says that people can get the daily recommended doses of vitamins and minerals in their diets by eating healthy meal and that many adults who take vitamin supplements may not need them.

"At the end of the day we have discovered that taking extra vitamins and minerals do more harm than good," says Byers.