Vitamin C, long in the vanguard of the war against wintertime sniffles, has fallen under scrutiny in recent years because scientific evidence of its effectiveness remains scant. Recently, researchers compiled data from 55 studies to find out if vitamin C really works to fight the common cold.

What the researchers wanted to know: Does vitamin C really work to prevent or treat colds?

What they did: The researchers compiled data from 55 different studies dating from 1940 to 2004 that looked at how well doses of at least 200 mg per day of vitamin C prevented or treated the common cold when compared with a placebo.

What they found: Most of the time, vitamin C didn't keep people from catching colds. However, when people, especially children, took vitamin C before they became sick, the illness didn't last as long. Most studies showed that the vitamin didn't help people who waited until after the onset of symptoms to take vitamin C, although one large study found that already-sick patients who took 8,000 mg on the first day of their illness got better faster. One group of people did seem to benefit more than others: Marathon runners, skiers, and soldiers exposed to extreme cold or physical exertion got sick 50 percent less often when they took vitamin C as a preventive measure.

What this study means to you: Vitamin C seems to work for people whose bodies are exposed to lots of physical stress, such as endurance athletes, skiers, soldiers, and other people who exercise intensely or spend a lot of time in freezing temperatures. For everyone else, especially children, starting a daily vitamin C regimen won't stop you from getting sick, but it might help you recover faster from the colds you do catch. Those who forget their daily dose of vitamin C are out of luck. Once you're already sick, one massive dose (8,000 mg) might help, though the jury is still out.

Caveats: Since this paper is a compilation of many studies, the authors had little control over the experimental design or the quality of the data. Also, the papers that showed the benefits of vitamin C for those who exercise were based primarily on marathon runners, and the results may not be applicable to people who participate in less taxing exercise regimens. None of the studies looked at how well vitamin C works as a treatment for already-sick children.

Find out more: If you don't like popping pills but still want a daily dose of vitamin C, the Ohio State University website has a list of foods that contain the nutrient naturally. The Linus Pauling Institute (named for the Nobel Prize-winning chemist who first popularized vitamin C) at Oregon State University has good vitamin C information on its website.

Read the article: Douglas, R.M. and Hemila, H. "Vitamin C for Preventing and Treating the Common Cold." Public Library of Science Medicine. June 2005, Vol. 2, No. 5, pp. 132-133.

Article online: http://medicine.plosjournals.org