People do not need to take vitamin supplements, new research has found, since they do "more harm than good" and could increase the risk of cancer and heart disease.
Dr Tim Byers, associate director for prevention and control at the University of Colorado Cancer Centre, in the US, looked at three widely taken over-the-counter pills and supplements, vitamin E tablets, beta-carotene and folic acid, and warned against exceeding the recommended daily amount.
One of the world's leading cancer experts, Dr Byers said: "We are not sure why this is happening but evidence shows that people who take more dietary supplements than needed tend to have a higher risk of developing cancer.
"When we first tested dietary supplements in animal models we found that the results were promising.
"Eventually we were able to move on to humans. We studied thousands of patients for 10 years who were taking dietary supplements and placebos.
"We found that the supplements were actually not beneficial for their health. In fact, some people actually got more cancer while on the vitamins."
There's no substitute for good food
Folic acid supplements are taken by about 230,000 pregnant women in Britain each year as it can help prevent spina bifida and other birth defects affecting the brain and spine.
But one study examined by Dr Byers' team found too much increased the chances of getting cancer by 56%.
Two trials of beta-carotene supplements found taking more than the recommended dose increased the risk of developing lung cancer and heart disease by 20%.
He added: "We have discovered that taking extra vitamins and minerals do more harm than good."
Dr Byers said that most people got their daily recommended doses of vitamins and minerals by eating healthy meals. "This is not to say that people need to be afraid of taking vitamins and minerals. If taken at the correct dosage multivitamins can be good for you. But there is no substitute for good food," he stressed.