A new Australian study reports that megadoses of vitamin C do not treat the common cold, but the findings are unlikely to end a long-standing controversy.

The study, by a team at ANU's National Centre for Epidemiology and Population Health, was funded by a major retailer of vitamins in Australia. It appears in this week's Medical Journal of Australia.

"It's time to question again the wisdom and utility of the wide practice of well nourished adults taking megadoses of vitamin C to treat the common cold," the authors write.

The researchers embarked on the study because previous evidence on vitamin C as a therapeutic was inconclusive. Study leader Dr Robert M. Douglas was involved in a Cochrane Collaboration review of 17 trials earlier this year, which found that while vitamin C won't stop you from getting a cold, taking a preventative 1g per day can reduce the duration of a cold by about half a day.

In the new study, four sets of medication (representing three different doses of vitamin C and a placebo) were randomly distributed to 323 volunteers from ANU's staff and student population. The volunteers were instructed to take their medication within four hours of experiencing cold symptoms, and to complete report cards on the development of the illness.

"The high doses of vitamin C didn't result either in shorter or less severe colds than those in the placebo low dose group," said Professor Douglas.

The last word?

But, as the Medical Journal of Australia asks, is this "the last word" on the question of vitamin C and the common cold?

Most definitely not, according to the Australasian College of Nutritional and Environmental Medicine (ACNEM), an organisation representing a minority of doctors who believe that humans need big doses of vitamin C to overcome the impact of acute infections.

President of ACNEM Dr Ian Brighthope, who discloses that as part of his practice he sells vitamins, describes the study as "poorly designed" and argues the authors are not qualified in nutritional and environmental medicine.

One of his main concerns is that the dose used in the study -- 1 to 3 grams of vitamin C -- is too small to treat an existing cold.

"It's like giving a 250mg of oral penicillin to a patient who has lobar pneumonia when the right dose is 3000mg," he said.

Dr Brighthope claims that when taken preventatively, the dose of vitamin C should be 3 to 5g. When used as a therapeutic, he says, 5 to 10g of vitamin C should be taken immediately a cold starts and repeated until symptoms subside.

Not only does was the dose in the study too low, he claims, but the average participant did not take it until around 13 hours after the cold started, despite the instructions.

President of another doctors' organisation, the Australasian Integrative Medicine Association, Dr Marc Cohen, agrees with Dr Brighthope.

"The dose was too little too late and it was not maintained," he said.

Dr Brighthope said that previous studies had also tended to rely on doses that were too small, and that such "replication of mistakes" posed a problem for evidence-based medicine.

Dr Cohen, who is also Director of Monash University's Centre for Complementary Medicine, argues that even if the dose regime had been correct, the study would only have been powerful enough to detect a large effect from vitamin C.

He said this was because the variability of responses was higher than the authors expected, and the number of study participants was lower -- more than half the volunteers failed to return their report cards.

Blackmores, the company that funded the study, was unavailable for comment. The authors say the company was not involved in the conduct or analysis of the trial or preparation of the article.

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