The common cold affects people worldwide, not just those who live in cold climates. Although almost everyone has experienced a common cold, researchers can't always measure how widespread the problem is. This is because most of us suffer through a cold without seeking treatment unless the symptoms (which might include a persistent cough, red nose, sneezing, and fever) become severe.
The best solution for the common cold is prevention. The popular media portrays many options and friends and family often make suggestions such as eating raw garlic or taking different vitamins and herbal supplements. But what (if anything) actually works to help prevent the common cold?
The study of vitamin C became popular after Linus Pauling, a Nobel Laureate in chemistry, claimed that it prevented many different diseases, including the common cold. Vitamin C is believed to have protective effects on body cells when there is an infection, reducing the risk of infections as well as their severity.
A high quality systematic review (1) including 29 studies involving 11,306 participants evaluated three impacts of vitamin C on the common cold:
Regular supplement to prevent the common cold
Regular supplement to reduce the duration and severity of symptoms, and
Treatment, to improve how long people experience symptoms and how sick they feel once they catch a cold
What the research tells us
The studies evaluating prevention showed that adults taking vitamin C supplements daily (doses ranged from 200 mg to 2000 mg) did not report fewer colds compared to people taking a placebo.
There was one small exception to this finding. The review found that people who do regular and intense physical exercise in cold weather (soldiers, skiers, marathon runners) and take vitamin C regularly did have a 48% decrease in the frequency of colds. However, an average older adult who doesn't exercise as intensely may not experience the benefits seen in people doing this type of intense training.
The research findings do suggest that taking vitamin C regularly as a supplement can decrease the number of days you feel sick. If the average cold lasts 8 to 10 days then you will feel like your cold has stopped about one day sooner when you take vitamin C regularly, and your symptoms may not be as severe.
A smaller number of studies measured vitamin C as a treatment after coming down with cold symptoms and found it is unlikely to make a difference to the length of time you feel sick (duration) or how sick you feel (severity).
In two studies the participants took 'mega' doses of vitamin C (6000 to 8000 mg) at the start of the cold. The findings suggest that taking a higher dose may decrease the duration of a cold by about half a day. However, more research is needed to be fully convinced and there is some uncertainty about whether the benefits outweigh potential side effects of taking larger doses of vitamin C.
There is still controversy around this issue. Although the benefit is small, some researchers suggest that it may be worthwhile to take vitamin C regularly as a supplement (1, 2). They argue that it is inexpensive and may be helpful for some individuals (2). The research studies varied greatly with respect to the length of time that people took vitamin C (from 2 weeks to 5 years). More research will help to evaluate if taking vitamin C for different lengths of time will produce the same results.