Impact of high-dose vitamin supplements 'not yet clear'

In collaboration with the Press Association

High-dose vitamin and mineral supplements may do more harm than good, an expert at the World Cancer Research Fund (WCRF) has warned.

Professor Martin Wiseman, the WCRF's medical and scientific adviser, explained that while low-dose supplements are recommended for some people, the effect of higher doses on cancer risk is difficult to predict.

For this reason, the WCRF advises people to get the vitamins and minerals they need by eating a healthy, balanced diet rather than taking high-dose supplements if they want to reduce their risk of cancer.

"Many people think they can reduce their cancer risk by taking supplements, but the evidence does not support this," Professor Wiseman said.

"Just because a dietary pattern that provides a relatively high level of a particular nutrient might protect against cancer, it does not mean that taking it in tablet form will have the same effect. In fact, at high doses the effect of these micronutrients is unpredictable and can be harmful to health."

The professor noted that high-dose supplements have previously tended to be tested on a select group of people - usually those who already faced a high risk of cancer - and that while some studies have suggested they might reduce risk, others have not - meaning that "the jury is still out".

"This means we simply do not know enough about what the effect will be for the general population to confidently predict the balance of risks and benefits. Some people may be doing themselves more harm than good."

Professor Wiseman also revealed that a number of studies have suggested a link between high doses of some supplements and an increased risk of certain cancers.

Beta-carotene supplements, for instance, have been found to raise the risk of lung cancer in people who smoke.

He also pointed out that supplements do not provide all of the beneficial substances obtained from foods and that more research is needed to confirm the effects of low-dose supplements on cancer risk.

"Until then, the best advice is to have a healthy, plant-based diet with lots of fruits and vegetables, rather than relying on supplements," he concluded.

Despite the uncertainty surrounding the impact of high-dose supplements on cancer risk, figures from the UK's Food Standards Agency suggest that 31 per cent of people take supplements, while around 15 per cent have taken a high-dose supplement in the past 12 months.

Yinka Ebo, health information officer at Cancer Research UK, said: "Many large studies have looked at the effects of vitamin supplements on cancer risk and most have found that these supplements have no effect. But some studies have found that, far from improving your health, high doses can be harmful and even increase the risk of cancer.

"The best way to get your full range of vitamins and minerals and help protect against cancer is to eat a healthy, balanced diet with a wide variety of fruit and vegetables."