Myths and Realities: Does Vitamin C Work for the Common Cold?

January 7, 2011

By Carolyn Bevan,  MD

Faculty Peer Reviewed

It starts with a tickle in your throat.  You feel a bit more tired after a day’s work, maybe your forehead feels a little warm.  You try to will it away, but over the next few days, it hits you: the congestion, runny nose and annoying cough.  Much to your dismay, you have a cold.  Determined not to give in without a fight, you drag yourself to the nearest drug store and buy the first mega-dose vitamin C supplement that meets your eye, which you promptly gulp down.  Then you go home, put your head under the covers, and hope it all goes away soon.

You’re not alone.  The average adult has two to four colds each year.  The cold is the second most common diagnosis in physicians’ offices, and the most common discharge diagnosis in the emergency room [1].  As we all know, in spite of its nagging prevalence, there is no cure for the pesky common cold.  Still, many of us reach for vitamin C supplements each year to stave off colds, to lessen duration, or to alleviate symptom severity.  The question is—does it really work?

In pre-clinical testing, vitamin C does have an impact on immune function.  Dr. Alfred Hess first identified ascorbic acid in the early 1900s as the deficient substance responsible for scurvy in British sailors.  Subsequently, researchers have shown that in in vitro and animal studies, Vitamin C increases neutrophil function, T cell proliferation, and interferon production, while decreasing virus replication, and protecting against oxidant damage during infection [2].  The benefit of vitamin C in human trials, however, has been slightly more difficult to interpret.

Until recently, it was generally accepted that vitamin C had no significant impact on the common cold.  In the early 1970’s, famed researcher Dr. Linus Pauling published a book based on his research about vitamin C, claiming that when given in doses of at least 1g daily, ascorbic acid significantly decreased the incidence and severity of the common cold.  His research, however, was not generally accepted by the medical community at the time [3].

Instead, one of the most often cited early human trials of vitamin C and the common cold was conducted at the NIH in 1975.  In the trial, Karlowski et al gave either 1g vitamin C or placebo to 311 NIH employees three times daily for nine months.  If a cold developed, study participants were instructed to increase of either vitamin C or placebo by an extra 3 grams daily.  In the 190 participants who finished the study, Karlowski found a modest, and perhaps dose dependent, decrease in duration and severity of colds.  The placebo he used, however, was lactose: a sweet little pill that was perhaps easy to distinguish from the tart ascorbic acid supplement.  Because of this, Karlowski did a post-trial analysis of whether or not participants could guess whether they were in the placebo or treatment group.  Based on this analysis, he concluded that the results of his trial could all be explained by failure of the double-blind protocol.  He concluded that vitamin C produced no real benefit in terms of prophylaxis or treatment of the common cold [4].

In a meta-analysis published later that year, Chalmers echoed Karlowski’s conclusions.  He found that cold duration decreased by 0.11 +/- 0.24 (SE) days in vitamin C groups, and thus was essentially worthless in treating the common cold [5].

For many years, this was taken as the final answer to the question of whether or not to recommend vitamin C during the cold season.  However, in 1995, ascorbic acid authority Harri Hemila, MD, a researcher who works at the Department of Public Health at the University of Helsinki in Finland, took a hard look at Karlowski and Chalmers’ conclusions and found that, in fact, the numbers did not necessarily fit their analysis.

In one paper, he asserted that Karlowski’s post-trial findings were not sufficient to explain the effect of vitamin C in the original NIH trial [6].  In a second review, he challenged Chalmers’ conclusions as well, stating that he misrepresented the data from the trials he referenced, while also including trials using unusually small dosages, which diluted any measurable effect.  Using the same studies referenced by Chalmers, excluding those that were insufficiently dosed, Hemila concluded that vitamin C (1-6g/day) decreased cold duration by 0.93 +/- 0.22 (SE) days.  He suggested that the researchers had dismissed the possible efficacy of vitamin C too readily, and concluded that, to the contrary, the majority of evidence points to a moderate but significant benefit to taking vitamin C for colds [3].

In fact, Dr. Hemila has produced or commented on a rather significant body of clinical research involving vitamin C and the common cold, all of which culminated in a 2007 Cochrane review of which he is first author.  The review, a meta-analysis, focused on fifty-six trials of vitamin C vs. placebo, given as either prophylaxis against or treatment of the common cold.  The main outcomes include incidence, duration, and severity of cold episodes.  Firstly, in a review of studies of prophylactic vitamin C’s effect on cold incidence, Hemila et al found that there was really no significant reduction in incidence in the general population (RR 0.98; 95% CI 0.95-1.00).  Interestingly, in a small subset of studies involving people under large amounts of physical or environmental stress, mainly marathon runners, skiers, and military troops training in subarctic conditions, there was a significant difference in incidence amongst prophylactic vitamin C users, with a relative risk of 0.50 (95% CI 0.38-0.66).  Meanwhile, prophylactic Vitamin C reduced cold duration by 13.6%, or in more concrete terms, from an average of twelve symptomatic days each year to an average of eleven.  In terms of severity, there was significant variability amongst the trials, but overall, a statistically significant but slight benefit was found in most studies, with vitamin C alleviating severity by approximately 8% overall [7].

The group then looked at therapeutic studies of vitamin C, in which participants began taking vitamin C after the onset of symptoms.  To analyze duration in these studies, Hemila et al used a weighted mean per episode standardized against the control group, setting the control group mean at 100.  When they studied duration, they found an effect size of -2.54 (95% CI -10.09, 5.02).  The mean difference in severity was found to be -.07 overall (95% CI -.016, 0.02). Based on these numbers, they concluded that there was no significant impact on duration, with an “equivocal” benefit of an 8g single dose taken immediately after symptom onset.  They also found no clinically significant effect on cold severity.  Of note, however, there were also no differences in adverse symptoms reported in vitamin C and placebo groups, even in some subjects taking up to 30g/day [7].

Overall, the Cochrane researchers conclude that, in normal populations not under significant physical or environmental stress, prophylactic or therapeutic vitamin C shows no practical clinical effect on the incidence, duration, or severity of the common cold.  The authors write that further research into vitamin C prophylaxis in the general population is unwarranted at this point, but they cite a small number of trials showing benefit using very high therapeutic doses (4 to 8 g on the day of onset of symptoms) as “tantalizing,” and suggestive that further research may reveal benefit in these higher therapeutic doses. [7].

So, at the end of the day, is there any benefit to taking a daily vitamin C supplement, or for chugging down that fizzy shot of mega-dose vitamin C when you feel a cold coming on?  If you are a marathon runner, or if you are planning a winter adventure in the arctic tundra, you should certainly consider a daily dose of vitamin C.  For the rest of us, it doesn’t seem to be worth the hassle and expense of adding one more pill to our daily routine.

On the other hand, regarding the effect of vitamin C taken at the onset of cold symptoms, the Cochrane group left a little room for interpretation.  The group was unable to identify a clinically significant benefit of therapeutic dosing based on the majority of currently available research.  However, they pointed to a few interesting trials showing evidence of benefit, yet to be verified, for therapeutic vitamin C preparations containing 4 to 8 grams.  Furthermore, in the general population, vitamin C’s side effect profile appears to be relatively benign.

So, in the words of Dr. Hemila, although “therapeutic trials with adults are only partly positive, it may still be reasonable to suggest testing vitamin C to treat colds” [8].  He goes on to remind us that trials are a commentary on group averages.  Some people will respond more, and some less, than the pooled results suggest.  As long as you consider the evidence, and adjust your expectations accordingly, there doesn’t appear to be much harm in reaching for some vitamin C when you feel a cold coming on.  If, however, you want a more solid endorsement of vitamin C’s effect before heading to the drug store, you’ll just have to wait.

Dr. Bevan is a former resident in internal medicine at NYU Medical Center.

Peer reviewed by Melanie Maslow, Infectious Disease Section Editor,  Clinical Correlations

Image courtesy of Wikimedia Commons


1. Simasek M, Blandino DA.  “Treatment of the common cold.”  Am Fam Physician.  2007 Feb 15;75(4):515-20.  Review.  PMID: 17323712.

2. Hemila H, Louhiala P.  “Vitamin C may affect lung infections.”  J R Soc Med.  2007 Nov;100(11):495-8.  Review.  No abstract available.  PMID: 18279551.Hemila

3. Hemila H, Herman ZS.  “Vitamin C and the common cold: a retrospective analysis of Chalmers’ review.”  J Am Coll Nutr.  1995 Apr; 14(2):116-23.  PMID: 7790685.

4. Karlowski TR, et al.  “Ascorbic acid for the common cold.  A prophylactic and therapeutic trial.”  JAMA. 1975 Mar 10;231(10):1038-42.  PMID: 163386.

5. Chalmers TC.  “Effects of ascorbic acid on the common cold.  An evaluation of the evidence.”  Am J Med. 1975 Apr;58(4):532-6.  Review.  PMID: 1092164.

6. Hemila H.  “Vitamin C, the placebo effect, and the common cold: a case study of how preconceptions influence the analysis of results.” J Clin Epidemiol. 1996 Oct;49(10):1079-84; discussion 1085, 1087.  PMID: 8826986.

7. Hemila H, Chalker E, Treacy B, Douglas B.  “Vitamin C for preventing and treating the common cold.” Cochrane Database of Systematic Reviews 2007, Issue 3. Art. No.: CD000980.  DOI: 10.1002/14651858.CD000980.pub3.

8. Hemila H.  “The role of vitamin C in the treatment of the common cold.”  Am Fam Physician.  2007 Oct 15;76(8):1111, 1115.  No abstract available.  PMID: 17992770.


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