Vitamin C Does Nothing for the Common Cold

Medscape

23-06-2025

This transcript has been edited for clarity.
If you aren't a 19th century British sailor, then you need to watch this video because — spoiler alert — vitamin C won't keep you from getting sick. I'm Dr Christopher Labos for Medscape, and this is On Second Thought .
If you were blockading the continent during the Napoleonic Wars, then squirting some lemon juice into your beer probably made the difference between your teeth falling out and your teeth not falling out. There were a lot of ways to die if you were a British sailor during the Napoleonic Wars and, amazingly, French guns were not in the top three!
The discovery of how to prevent scurvy with vitamin C is a great medical detective story, and I highly recommend Stephen Bown's book, Scurvy: How a Surgeon, a Mariner, and a Gentleman Solved the Greatest Medical Mystery of the Age of Sail . But if your idea of sailing is taking the IKEA ferry — by the way, it's free and gives you a great view of the Statue of Liberty — then scurvy is probably not your biggest problem.
You probably take vitamin C because someone told you it prevents the common cold, and that person was probably Linus Pauling. Now, Linus Pauling was a very smart guy. He won two unrelated Nobel Prizes and, as far as I know, I haven't won any. So, when he wrote a book called Vitamin C and the Common Cold , people listened. And for some reason they don't seem to listen to me… Please follow me on X or Bluesky; social media is how I measure my self-worth.
In the book, he told people to take 3000 mg of vitamin C every day to live longer and healthier. He predicted vitamin C would eliminate the common cold and extend the human lifespan. In interviews, he claimed that people who took optimum amounts of vitamins and supplements would live 25-35 years longer and would be free of diseases.
Now, clearly the work of Nobel laureates needs to be taken seriously. But there is a condition called "Nobel disease" where, basically, you win a Nobel Prize and you think you're an expert in everything, and then subsequently go a little bit crazy and believe all kinds of nutty stuff. For example, Charles Richet won the 1913 Nobel Prize in Medicine and he believed in ghosts and telepathy; Pierre Curie attended seances; and a surprisingly large number of Nobel laureates became eugenicists. And then there was Kary Mullis, inventor of the polymerase chain reaction (PCR). Well, if you didn't know about that one, Google "Kary Mullis and fluorescent talking raccoon." You heard me: fluorescent talking raccoon. I'll wait here.
Now, Linus Pauling was not any of these things, although he did say people with sickle cell trait should get a tattoo on their forehead so nobody accidentally had babies with them. And he also said some stuff about aborting babies with sickle cell disease. So… eugenics light, maybe? But to be fair, a lot of people in the 1930s held similar views, and it's unclear how much the general public in the US really knew about what was going on in Germany.
But...
This was in 1968?! Jesus! Okay, never mind about that.
So anyway, being a Nobel laureate doesn't make everything you say inherently right. Let's do some math. Does vitamin C prevent the common cold? Because we aren't doing the cancer stuff; I get too much hate mail as it is. Okay, fine: Vitamin C doesn't treat cancer. There! I said it! Alright? Everybody happy? I said it!
But let's do the cold and flu stuff because there's an important lesson here. Does vitamin C prevent the common cold? To answer this question, I'm going to be using the data from the 2013 Cochrane review titled "Vitamin C for Preventing and Treating the Common Cold." It summarized 29 trials, including 11,306 participants, and is one of the most misquoted Cochrane reviews I have ever seen.
Let's start with treatment. Does taking vitamin C when you get sick make you better? No . There were 10 studies that looked at this question, and these were people taking vitamin C when their symptoms started. It made no difference in symptom duration or severity. If you start taking vitamin C at the onset of symptoms, it does nothing. So, if you're somebody who starts popping vitamin C tablets when you get sick, this Cochrane review does not support that practice. The commercials and celebrity endorsements are lying to you.
The only reason the marketing geniuses behind vitamin C can say anything positive is because there's another way to take vitamin C — and no, I don't mean as a suppository. You can take it as a regular supplement every day of your life, which is great for capitalism but inconvenient for you as a healthcare user. So then the question becomes, if you take vitamin C every day of your life as a regular supplementation strategy, will that prevent you from getting sick? Also no . The incidence of common colds is not reduced in the general population with regular vitamin C supplementation. It says that very clearly in the review.
The only benefit observed in the 2013 review was vitamin C's effect on symptom duration. If you take vitamin C every day of your life, when you get sick — and you will still get sick the same number of times —your symptoms will go away faster. How much faster, you ask? I'm glad you did. According to this analysis, it reduces cold symptom duration by 7.7% on average. And what does that mean? Well, let's assume your cold lasts for 5 days. That is 120 hours for those of us living on planet Earth. If we take the vitamin C meta-analysis at face value, your cold will go away 9 hours faster. You're spending $30 a month (or $360 a year) for 9 hours of symptom relief. I'm not sure that's cost-effective.
So, if that's the case, why do people claim that vitamin C can prevent the common cold? Well, welcome to the wonderful world of subgroup analysis — it's kind of nuts here! If you limit the Cochrane review to the five studies that tested vitamin C in periods of short-term physical stress or cold temperatures, that's where you see a benefit. Let's break that down.
Three studies tested the effect of vitamin C among ultramarathon runners in South Africa, so that was the short-term physical stress part — because running a marathon is bad enough, but running an ultramarathon is incrementally worse. The cold temperatures (which made up the bulk of this subgroup) were examined in two studies. The first study observed Canadian soldiers on military maneuvers, because, as you know, Canada's a freezing wasteland and I ride my moose to work every day at my igloo medical clinic. The other study (which is where the bulk of the cold temperature patients came from) involved skiers. You might think, Okay, these were Olympic skiers enduring high-stress and cold-weather environments . But surprisingly, no. It was a study of children attending a ski school in Switzerland, which actually sounds like a pretty good vacation and I assume cocoa was involved.
What's often left out of this discussion is the fact that other, longer-duration studies, like one in US Marines and another one in kids attending swim schools, didn't show a benefit . So, you really have to pick and choose to see a signal here. In the general population, there's no benefit — only in this very eclectic and specific subgroup of patients.
If you know something about statistics, you know how dangerous subgroup analysis can be. Cut up the data into ever thinner salami slices and you can find some wild and ludicrous results. Remember the ISIS-2 trial? It showed that aspirin efficacy post-myocardial infarction varied by astrological sign. That's the quintessential example of how multiple-hypothesis testing can generate spurious results.
Random chance is a major factor in life. Random chance is why you can use real data to show that the divorce rate in the UK correlates with the number of movies that Disney has released in any given year. Go data dredging and you can find any association if you torture the data enough.
Overall, vitamin C does nothing for the common cold. Even at the most forgiving, it shortens symptoms by a few hours, which I think is just spurious given the incredible heterogeneity in the published research. But if you ignore all that, you only see a clinically meaningful difference if you're a South African ultramarathoner, a Canadian soldier, or a child attending a ski school in Switzerland. And you're probably none of those things — just like you're not a 19th century British sailor.