Questions raised over vitamin C's cold benefits

By staff reporter

- Last updated on GMT

Related tags Vitamin Common cold

A review of 30 studies has concluded that a daily vitamin C
supplement does not offer protection from common colds, adding to
the ongoing debate about the vitamin efficacy on colds.

The review, published in the latest issue of The Cochrane Library​, looked at studies conducted over several decades and included more than 11,000 people who took daily doses of at least 200 milligrams. The reviewers report that the vitamin did little to reduce the length or severity of a cold. "It doesn't make sense to take vitamin C 365 days a year to lessen the chance of catching a cold,"​ said co-author Harri Hemilä, from the University of Helsinki in Finland. The image of vitamin C supplements with consumers is already strong. According to Frost & Sullivan, the US market generated $151.7m (€127.4m) in 2005. In Europe, revenue was calculated at $160.3m (€134.6m) for 2005, and is expected to grow to $192.5m (€161.6m) by 2011. On a positive note, however, the reviewers report that the vitamin could halve the likelihood of catching a cold for people exposed to periods of high stress - such as marathon runners, skiers and soldiers on sub-arctic exercises. The reviewers, from the Australian National University and the University of Helsinki, did note that the number of trials was limited and these varied in quality. They also noted that one large trial reported significant benefits from an eight-gram dose at the onset of symptoms. The authors added: "Two trials using five-day supplementation reported benefit, pointing to the need for further therapeutic trials to examine the effects of large vitamin C doses. Finally, none of the therapeutic trials carried out so far examined children, even though the regular supplementation trials reported substantially greater effect on duration in children."​ Hamila added that he would like to see more studies on vitamin C and colds in children and vitamin C and pneumonia. Vitamin C is not a panacea, but it is not useless either, he said. The current recommended daily allowance of vitamin C is 60 milligrams. On the other side of the debate, a Japanese trial, reported in the European Journal of Clinical Nutrition​ (2005, doi:10.1038/sj.ejcn.1602261) that a daily supplement of either 50mg (low-dose) or 500 mg vitamin C for five years reduced the risk of suffering from a common cold three or more times during the survey period was 66 per cent lower for the high-dose group. The findings have been challenged by the Alliance for Natural Health (ANH), a UK-based, internationally-focused, legal-scientific, non-governmental organisation. Dr Robert Verkerk, executive director of the ANH said: "These headlines have been triggered by a small update to an existing review that does not reflect any significant new research findings. The review maintains all the flaws of the original Cochrane review on vitamin C and the common cold, as published in 2004. This boils down to the blatant misuse of a minor update of a review to make a major news story that is anti-natural health."​ Dr Damien Downing, ANH's medical director and a practising Harley Street physician, added: "Fortunately, large numbers of doctors, practitioners and even consumers know just how effective multiple, daily doses of vitamin C can be for preventing, or reducing the severity of, the common cold and other infections. So many people in today's society are under stress, and frequent 500 mg to 1000 mg doses of vitamin C are one of the most cost effective ways of supporting the body's immune system."​ Source: Cochrane Database of Systematic Reviews​ 2007, Issue 2, doi: 10.1002/14651858.CD000980.pub2 "Vitamin C for preventing and treating the common cold (Review)" ​Authors: R.M. Douglas, H. Hemila, E. Chalker, R.R.D. D'Souza, B. Treacy

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