Dietary supplements could adversely affect your health if taken in excess, according to a recent study.

Researchers at the University of Colorado found that over-the-counter dietary supplements, despite being advertised to promote health, could 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," Tim Byers, associate director for cancer prevention and control at the CU Cancer Center, said in a statement.

For the study, researchers wanted to explore whether or not taking extra vitamins and minerals would reduce cancer risk even further. The line of research started 20 years ago with the observation that people who ate more fruits and vegetables tended to have less cancer.

"When we first tested dietary supplements in animal models we found that the results were promising," Byers said. "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."

Based on their findings, researchers concluded that the supplements were not beneficial for people's health.

"In fact, some people actually got more cancer while on the vitamins," Byers said.

One of the trials examined the effects of beta-keratin supplements, researchers found 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," Byers explained. "If taken at the correct dosage, multivitamins can be good for you. But there is no substitute for good, nutritional food."

People can get the daily recommended doses of vitamins and minerals in their diets by eating healthy meals. Byers noted 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," Byers said.