Want to live a long, healthy life free from cancer and other deadly diseases? Just pop a pill.

That is the message from firms marketing antioxidant supplements such as vitamins A and E received by an understandably eager public.

The tablets work by neutralising destructive atoms known as free radicals which have been linked to health problems ranging from cancer to heart disease.

But serious questions have now been raised about their effectiveness.

Today new research suggests that far from protecting people from death and poor health, these so-called superhealthy supplements could be killing them.

A review of 67 studies involving more than 230,000 people found that "beta-carotene, vitamin A, and vitamin E seem to increase mortality".

Experts at Copenhagen University Hospital in Denmark also warned that there was "no convincing evidence" that taking any of the five antioxidants which they investigated would actually prolong life.

It is the latest twist in the increasingly confusing mix of advice leaving many wondering what really is best for their health.

In this case the issue seems to be how much antioxidant is good for you, and how much might be harmful. The review, published by The Cochrane Collaboration, focused specifically on trials of beta-carotene, vitamin A, vitamin C, vitamin E, and selenium.

People taking part were either healthy (and were taking part in primary prevention trials) or had a disease (and were taking part in secondary prevention trials).

When the different antioxidants were assessed separately and low risk of bias ie more statistically reliable trials were included and selenium excluded, vitamin A was linked to a 16% increased risk of dying, beta-carotene to a 7% increased risk and vitamin E to a 4% increased risk.

There was no significant detrimental effect caused by vitamin C, but even then authors warned that there was no evidence to disprove that it too might raise death rates. The review authors said: "We found no evidence to support antioxidant supplements for primary or secondary prevention of health problems. Beta-carotene, vitamin A and vitamin E given singly or combined with other antioxidant supplements significantly increase mortality.

"There is no evidence that vitamin C may increase longevity. We lack evidence to refute a potential negative effect of vitamin C on survival.

"Selenium tended to reduce mortality but only when high-bias risk trials which are less reliable were considered. Accordingly, we need more research on vitamin C and selenium."

While further studies are awaited, dieticians in Scotland advised people to try to obtain all the antioxidants they need through diet, rather than overdosing on supplements.

Rona Young, registered dietician in Glasgow and member of the British Dietetic Association, said: "I'm sure most registered dieticians would agree with me that the majority of people should be able to get all the nutrients they need through the five main food groups - eating plenty of fruit and veg, plenty of starchy foods like rice and pasta, some milk and dairy, some meat, fish and beans for protein and a small amount of food high in fats and sugars.

"If people do want to take something as a safety net' we would advise them to take a multivitamin with no more than 150% of the recommended daily amounts of antioxidants. We recognise that high doses of certain nutrients can be toxic and dangerous."

Meanwhile, supporters of supplements maintain that they are a beneficial part of a healthy lifestyle.

Patrick Holford, a nutritionist who has formulated some supplements for the firm Biocare, said: "When used properly, in combination with eating a healthy diet, getting plenty of exercise and not smoking, antioxidant supplements can play an important role in maintaining and promoting overall health."