New York, April 21 (IANS): Over-the-counter dietary supplements you thought were good for you may actually increase cancer risk if taken in excess of the recommended daily amount, says a new research.

"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," said lead researcher Tim Byers from the University of Colorado Cancer Centre.

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. They studied thousands of patients for 10 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," Byers said.

One trial exploring the effects of beta-keratin supplements showed that taking more than the recommended dosage increased the risk of 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.

"If taken at the correct dosage, multi-vitamins can be good for you. But there is no substitute for good, nutritional food," he concluded.

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

The findings were presented at the American Association for Cancer Research Annual Meeting 2015 in Pennsylvania, US.