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Common colds: Does vitamin C keep you healthy?

Last Update: April 23, 2014; Next update: 2017.

Taking vitamin C every day to try to prevent colds does not protect most people from colds. It only slightly shortens the amount of time that they are ill. Starting to take vitamin C once you already have cold symptoms will not have any effect on your cold.

You need a certain amount of vitamin C to stay healthy and well, and most people get enough in their daily diet. Vitamin C (ascorbic acid) can be found in fruits and vegetables, and citrus fruits and berries have especially high levels of vitamin C. Medical conditions that are caused by vitamin C deficiency, such as scurvy, are practically nonexistent in countries like Germany.

Despite this, many people take vitamin C supplements every day in order to prevent a number of different illnesses, particularly common colds. Some of these products have more than one gram of vitamin C, which is more than ten times the recommended daily amount. Because the body cannot store vitamin C, the excess vitamins are usually flushed out of the body in urine within a few hours. The German Institute for Risk Assessment (Bundesinstitut für Risikobewertung, BfR) considers 100 milligrams of vitamin C per day in your diet to be enough.

Researchers from the Cochrane Collaboration – an international network of researchers – looked into the question of whether taking large doses of vitamin C can protect against colds or relieve the symptoms. To find out, they analyzed studies comparing vitamin C with a product that did not contain any active ingredient (a placebo).

29 studies involving more than 11,000 children and adults tested whether regularly taking at least 200 mg of vitamin C could help prevent colds. Most of the studies used a dose of 1,000 milligrams of vitamin C or more per day. Some of the participants took the vitamin C over a period of several years.

Research results

The studies showed that it was not possible to prevent colds by taking vitamin C every day over a longer period of time. But doing so did shorten the amount of time that people were ill by about 10%. In other words, a cold that would have lasted ten days was over in nine. The cold symptoms were also a bit milder. Vitamin C did not shorten the length of colds in men and women who started taking it only after they became ill.

Some of the studies looked at whether vitamin C can prevent colds in people exposed to short periods of very strenuous physical activity, often in connection with extremely cold temperatures, like marathon runners or soldiers doing winter exercises in a mountainous region. In these studies, the participants started taking vitamin C two to three weeks before the very strenuous activities as a means of preventing colds. It was found that doing so reduced their risk of developing a cold by about half.

Taking very high doses of vitamin C regularly may cause diarrhea, but study participants who took vitamin C did not report more side effects than those who used a placebo.


  • Bundesinstitut für Risikobewertung (BfR). Verwendung von Vitaminen in Lebensmitteln. Berlin: BfR.2004.
  • Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Sys Rev 2013; (1): CD000980. [PubMed: 23440782]
  • IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

    Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

    Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

© IQWiG (Institute for Quality and Efficiency in Health Care)

IQWiG (Institute for Quality and Efficiency in Health Care)

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