Taking vitamin C to combat colds is a waste of time, scientists have revealed.

They found that the supplements, commonly perceived to be a tonic for winter ills, have little preventative effect and are no use at dealing with symptoms.

Only marathon runners, skiers and others exposed to extreme cold or stress for short periods should bother taking the pills, the study showed.

The researchers based their conclusions on an analysis of 30 studies carried out over six decades and involving more than 11,000 patients.

'It just doesn't make sense to take vitamin C 365 days a year to lessen the chance of catching a cold,' they insisted.

Although the results were based on supplement use, the researchers said drinking orange juice or eating an orange - both good sources of vitamin C - were equally useless.

Their review, published in the Cochrane Library, a respected medical journal, looked at whether those who regularly took vitamin C tablets were less likely to catch colds than others. It also assessed the extent and duration of the symptoms when daily takers did catch a cold.

All those studied took at least two grams of the vitamin a day - around four times the dose normally found in supplements in shops.

Analysis of the figures, drawn from studies conducted around the world, revealed the pills had little benefit. It found that those taking a daily dose of vitamin C were just two per cent less likely to catch a cold. Their symptoms would clear up only marginally more quickly.

The researchers, from the University of Helsinki in Finland and the Australian National University in Canberra, said this would equate to the average person suffering a cold for 11 days a year instead of 12.

'It would not seem reasonable to ingest vitamin C regularly throughout the year if the only anticipated benefit is to rather slightly shorten the duration of colds which occur for adults two or three times per year,' they said.

The study also showed that starting to take the vitamin at the first sign of symptoms did little to hasten recovery.

It did find, however, that the vitamin benefited marathon runners, skiers and soldiers training in the Arctic, suggesting it is beneficial if the body is under extreme stress. Last night British experts said vitamin C is likely to benefit only those lacking it in the first place.

Hugh Pennington, a leading microbiologist from Aberdeen University, said the research showed that vitamin pills or even a glass or two of orange juice do little to dry up the sniffles.

However, taking them will not do any harm - and simple belief that they work could still help sufferers feel better, he said.

'I am not surprised they found that vitamin C was no help, I think that the public's faith in vitamins is slightly misplaced,' he said. 'If you want to take orange juice and it makes you feel good, so much the better. But it isn't going to make your cold go away any quicker.' Advising cold sufferers to 'grin and bear it', he warned: 'I don't think there is any treatment out there that will do anything for a cold.

'Colds are caused by many different viruses. By the time you have got a runny nose, fever or sore throat it is probably a bit on the late side, even if there was something that would work. You've really just got to stick it out.'

Scientists recently concluded that echinacea, another widely-used cold remedy, really does work.

The U. S. review of 14 research studies concluded that daily doses of extracts of the plant - also known as the purple coneflower - can cut the chances of catching a cold by more than half.

It also reduced the duration of a cold by 1.4 days among those using it as a treatment, said researchers from University of Connecticut School of Pharmacy.