“Taking Vitamin C prevents the common cold.”

Evidence shows that vitamin C could be justified for people exposed to brief periods of severe physical exercise or cold environments and could halve the risk. Taking vitamin C regularly had consistent small benefits on duration and severity of colds. The trials in which vitamin C was given at the onset of colds did not show any benefit in doses up to 4 grams daily.

In controlled trials in the general human population, vitamin C at a dose greater than 1 g/day did not prevent common colds. However, in 5 trials with participants undertaking heavy physical activity, vitamin C halved the incidence of colds. In 15 trials (n = 6244), regular supplementation of 1 g or more of vitamin C per day decreased the severity of colds by 15%.

In children, 1 to 2 g/day vitamin C shortened colds by 18%. The severity of colds was also reduced by regular vitamin C administration. Regular supplementation trials have shown that vitamin C reduces the duration of colds, but this was not replicated in the few therapeutic trials.

Regular ingestion of vitamin C had no effect on common cold incidence in the ordinary population, based on 29 trial comparisons involving 11,306 participants. However, regular supplementation had a modest but consistent effect in reducing the duration of common cold symptoms, which is based on 31 study comparisons with 9745 common cold episodes.

Our literature review revealed that vitamin C is not effective at preventing the common cold in the general adult population; however, it is effective at preventing colds when consumed regularly by athletes training in subarctic conditions. We also found that regular vitamin C consumption may reduce the duration of cold symptoms in both adults and children, but it does not decrease the severity of cold symptoms.

It was found that in terms of the average number of colds and days of sickness per subject the vitamin group experienced less illness than the placebo group, but the differences were smaller than have been claimed and were statistically not significant. However, there was a statistically significant difference (P <0.05) between the two groups in the number of subjects who remained free of illness throughout the study period.

The idea that vitamin C can prevent colds became popular in the 1970s, but research has largely debunked this myth. While taking vitamin C regularly doesn't appear to reduce the chances of catching a cold, some evidence suggests it might slightly shorten the duration of a cold or lessen the severity of cold symptoms.

Popular belief is that vitamin C can cure the common cold. However, research about this claim is conflicting. Although not fully proven, large doses of vitamin C may help reduce how long a cold lasts. Large doses of vitamin C do not protect against getting a cold.

Compared to placebo, vitamin C significantly decreased the severity of the common cold by 15% (95% CI 9–21%). The direct comparison of the effect of vitamin C on mild and severe symptoms was limited to five comparisons which found that vitamin C had a significant benefit on the duration of severe symptoms.

Regular vitamin C intake at doses of at least 200 mg/day may reduce the incidence of the common cold in people who exercise intensely, are exposed to cold environments, or have marginal vitamin C status. However, in the general population, taking vitamin C prophylactically does not appear to reduce the risk of the common cold, although it does appear to modestly reduce the duration of the cold and ameliorate the symptoms.

Across 24 trials with nearly 11,000 participants, people who took 200 to 2,000 milligrams a day of vitamin C for an average of three months were no less likely to catch a cold than those taking a placebo. When they did catch a cold, though, they were sick for slightly less time—about half a day less—than the placebo takers.

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. It was found that doing so reduced their risk of developing a cold by about half.

Our meta-analysis on vitamin C and the common cold found that vitamin C did not decrease the average number of colds in general community trials (2). However, we found that in five trials with 598 physically active participants vitamin C decreased common cold risk by 52% (P < 0.00001) (2). In one of the largest trials to date, Anderson (1972) (5) found that the occurrence of outcomes 'not confined to the house', 'not off work', and 'not ill during the trial' because of common cold related symptoms were all about 8 percentage points lower in the vitamin C group than in the placebo group.

Vitamin C as a supplement before a cold starts does not prevent it but may reduce its duration and severity. Vitamin C did not reduce the number of people who caught colds. While these results were consistent across studies, their effect was small.

While vitamin C is safe, there is no evidence for its ability to prevent the common cold. Although the Cochrane review and more a recent meta-analysis by Hemilä and Chalker demonstrated statistical significance in shortening the duration of symptoms, it was a minimal reduction with little clinical significance.

Vitamin C is significant to human body and plays a role in reducing inflammatory response and preventing common cold. In a controlled but non-randomized trial, 85% of the 252 students treated experienced a reduction in symptoms in the high-dose vitamin C group.

Major health authorities like the NIH and CDC state that vitamin C does not prevent colds in the general population but may slightly reduce duration; benefits are seen only in extreme stress populations like athletes. This aligns with Cochrane reviews spanning decades of trials.