Britain: A leading study has warned that millions of people who take dietary supplements to boost their health may be doing themselves more harm than good.

Scientists have claimed taking pills and capsules, like folic acid, vitamin D and calcium, do not reduce the risk of cancer. They also warned that antioxidant pills - natural chemicals that boost health - such as beta-carotene, and vitamins C and E may even promote the disease, a daily reported.

The study published in the Journal of the National Cancer Institute cautioned that individuals may be toying with a "two-edged sword" that might do them harm.

They said people are being misled by "messages from supplement manufactures" stressing the health benefits of their products, including cancer prevention.

"Undoubtedly, use is driven by a common belief that supplements can improve health and protect against disease, and that at worst, they are harmless," wrote the panel of five experts, led by Dr Maria Elena Martinez, from the University of California at San Diego.

"However, the assumption that any dietary supplement is safe under all circumstances and in all quantities is no longer empirically reasonable. A nutrient may be associated with protection in one tissue and harm in another," they stated.

A third of UK adults take some form of dietary supplement most days and the industry is worth 675million pounds a year.

Yinka Ebo, Cancer Research UK's senior health information officer, said: "This scientific evidence should give people good reason to think twice about relying on supplements.

"The best way to get a full range of vitamins and minerals is to eat a healthy, balanced diet with a wide variety of fruit and vegetables. For most healthy people there should be no need to take supplements," Ebo stated.

Dr Carrie Ruxton, of the Health Supplements Information Service, added: "They are not intended to treat, prevent or cure any disease."