C does not necessarily stand for a cold cure
The Irish Times
Health Supplement, p. 13
10 February 2009
DOES IT WORK?: Vitamin C has been linked with cold prevention but it is more useful for easing physical activity, writes DONÁL O’MATHÚNA
VITAMIN C is often used to prevent and treat the common cold, but has been controversial for many decades. This debate provides a good example of how claims are made about supplements and shows the importance of examining the details. In many situations we would like a “yes” or “no” answer: it works or it doesn’t. The vitamin C story reveals that a better answer is, “it all depends.”
The Pauling Controversy
This vitamin C debate began with the publication in 1970 of the book, Vitamin C and the Common Cold . The author, Linus Pauling, was one of the most respected scientists of the 20th century, having won the 1954 Nobel Prize in Chemistry and the 1962 Nobel Peace Prize for his work concerning nuclear weapons. Pauling was also a successful teacher and author, effectively communicating complex scientific concepts to the public.
Yet many of his ideas on health promotion and supplements remain controversial.
In his 1970 book, Pauling discussed about 30 studies on vitamin C and the common cold. He also published his findings in professional journals, but focused on only four studies.
Together, these showed that people taking vitamin C got fewer colds than those taking a placebo.
In another article he discussed only the two most beneficial trials and showed that those taking vitamin C recovered more quickly from colds.
Most of the benefits came from one short study conducted with children attending a ski school in the Swiss Alps.
Given Pauling’s reputation, and the huge interest in finding a cure for the common cold, several studies of vitamin C were conducted during the 1970s.
Two systematic reviews of these studies concluded that vitamin C did not provide significant benefits. They found that people did not get fewer colds when taking vitamin C and that, on average, a cold lasted a few hours less when taking vitamin C. That seemed to settle the issue medically, yet public interest in vitamin C continued.
What the studies show
Controlled studies continue to be conducted, but with inconsistent results. There have been many developments in the methods used to evaluate and review treatments.
An important realisation is that when people review research, their inherent biases can influence the studies they select and emphasise. Thus, Pauling focused on only four of the 30 studies available to him, yet he never explained why he chose these and not the others.
Reviews published in the 1970s and 1980s focused on studies with less beneficial results, but did not explain their selection process. Such an approach increases the risk of reviewers finding the results they wanted in the first place.
The best way to review the research is to look for all the studies conducted on a topic. Such a review is freely available in Ireland at http://www.TheCochraneLibrary.com. This found 56 individual studies in which vitamin C was compared with a placebo.
Most studies used doses of between 200mg a day and 2g a day. They had a range of results, but several patterns appeared in the details.
In everyday circumstances, taking vitamin C on an ongoing basis does not lead to fewer colds. The one exception is when taken immediately before severe physical stress. Six studies involving skiers, soldiers in sub-arctic conditions or marathon runners found that taking up to 1g of vitamin C a day reduced the incidence of colds by half.
Ongoing use of vitamin C did have some benefits when people got a cold. In general, the colds were 8 per cent shorter for adults and 14 per cent shorter for children. This would mean that, over an average year, an adult would have symptoms for one day less and a child for four days less. Whether this would be worth the cost of using supplements continuously is questionable.
Several studies have tested people taking 1-3g of vitamin C a day as soon as cold symptoms begin. While a few studies had beneficial results, the majority did not and on average the results showed no benefits.
Vitamin C is safe to take, but large doses can lead to some intestinal problems. By the end of his life, Pauling said that he took 18g of vitamin C a day, increasing to 40g a day when he felt a cold starting. While such large doses may not have harmed him, it is questionable whether they did him much good.
There is clear evidence of benefits from taking 1-2g a day in the weeks before major physical exertion, such as a skiing trip or marathon.
Long-term supplementation may slightly reduce the severity of a cold when you get one, but it won’t reduce how many colds you get.
Children benefit more this way than adults. Once you get a cold, extra vitamin C appears to be of little benefit. Most people get enough vitamin C by eating plenty of fruits and vegetables, especially citrus fruits, green vegetables and peppers.