Does vitamin C prevent colds?

Photo of citrus fruits

Taking vitamin C every day to try to prevent colds won't protect most people from colds. It only slightly shortens the amount of time that they're ill. Starting to take vitamin C once you already have cold symptoms won't 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 non-existent in countries like Germany.

Despite this, many people take vitamin C supplements every day in order to prevent a number of different illnesses, particularly colds. Some of these products have more than one gram of vitamin C, which is more than ten times the recommended daily amount, which is about 100 milligrams (mg). Because the body can't store vitamin C, the excess vitamins are usually flushed out of the body in urine within a few hours, so they end up in the toilet.

Studies on vitamin C

Researchers from the – 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 didn't contain any active ingredients (a placebo).

29 studies, involving more than 11,000 children and adults, tested whether the regular use of supplements containing at least 200 mg of vitamin C prevented colds. Most of the studies tested a dose of 1,000 or more mg of vitamin C per day. Some of the participants took the vitamin C over a period of several years.

Research results

The studies showed that it wasn't 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 percent. In other words, a cold that would have lasted ten days was over in nine days. The cold symptoms were also a bit milder in people who always took vitamin C.

Other studies show that taking vitamin C only after becoming ill didn’t shorten the length of colds in men and women. It didn’t relieve their symptoms, either.

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 extremely cold temperatures. Examples include marathon runners or soldiers doing winter exercises in a mountainous region. The study participants started taking vitamin C two to three weeks before the activities, with the aim 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 the study participants who took vitamin C didn’t report having more side effects than those who used a placebo.

Domke A, Großklaus R, Niemann B et al. Verwendung von Vitaminen in Lebensmitteln - Toxikologische und ernährungsphysiologische Aspekte. Berlin: Bundesinstitut für Risikobewertung (BfR); 2004.

Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev 2013; (1): CD000980.

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. can provide support for talks with doctors and other medical professionals, but cannot replace them. 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.

Comment on this page

What would you like to share with us?

We welcome any feedback and ideas - either via our form or by We will review, but not publish, your ratings and comments. Your information will of course be treated confidentially. Fields marked with an asterisk (*) are required fields.

Please note that we do not provide individual advice on matters of health. You can read about where to find help and support in Germany in our information “How can I find self-help groups and information centers?

Über diese Seite

Updated on December 11, 2023

Next planned update: 2026


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

How we keep you informed

Follow us on Twitter or subscribe to our newsletter or newsfeed. You can find all of our films online on YouTube.