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Vitamin C would be a cheap and easy weapon against Doctor Anna’s cold, but does it work?

Vitamin C is cheap and Doctor Anna’s cold severe; it would be wonderful if she could treat her illness in such an easy manner:

I immediately received good advice from various people and well-wishers (thank you). What most people told me was: sleepdrink water, and take vitamin C. Sleep and water – sure, I buy those arguments any day, but what about vitamin C (ascorbic acid in science-lingo)?

What is the truth behind this old claim of vitamin C beating colds and the flu? Is it placebo or does it really work?

Does vitamin C really help against a cold – a complicated question!

This simple question turned out to be more difficult to answer than I had anticipated. Human biology is tricky as it is hard to control for all outside parameters. You just cannot lock a group of people into a room and force them to do exactly the same thing for weeks, or even months…

Despite giving the test groups questionnaires, you might end up comparing Dorothy, who is a secret smoker, with Hans, who lied about his drinking habits, with Curtis, who decided to eat only meat and carrots for the duration of the study. Of course, this skews the results. This is why you need many people in a study and why it is important to not blindly look at one single study, but many compiled into a so-called meta-study.

Vitamin C and its effect on recovering from the common cold

I was struck by the low number of participants in many of the studies testing the efficiency of vitamin C against the common cold. It is expensive to run a study, but if too few participants are used in a study you can, at best, call it a “pilot study”; it is impossible to draw any clear conclusions from it. Still, several of these studies were published in good journals like the Lancet (but back in the 1970s). Hmmmm…I am not impressed.

Vitamin C and cold

Vitamin C and the bigger picture

I was almost jumping for joy when I started to find several meta-analyses on the topic. A meta-analysis means that some very clever people have decided to search the literature databases, request the raw (original) data from the studies, and run their own statistical analysis of all the studies combined. Ta-daaa! Suddenly you have a very large number of participants and all the smaller studies not wasted.

The clever meta-analysis-people put in some restrictions regarding which studies to include, for example, faulty studies should not be included. One example of a very faulty study (different topic) is the MMR vaccine-autism-link paper from Andrew Wakefield. In this study, Wakefield showed that of 12 patients, 8 showed autism symptoms after the MMR shot. The problem was that the children had already shown signs of autism before the vaccination. One might just as well argue that the carrots they happened to eat that day in the cantina caused their autism. Such studies should not be included in a meta-analysis. They are bad and can cause a lot of harm.


Vitamin C and the common cold: The analysis

The common-cold-vitamin C-meta-study included 11 306 participants, which is a very large number. 598 of these were athletes. The meta-analysis people found that the cold duration was shortened by 8 % for adults and around 14 % for children. This is hardly relevant since the common cold rarely exceeds a week (when this treatment would be effective). If a cold lasts a week, 8 % represents about 14 hours for an adult. Hmmm…I am not convinced.

To achieve this effect a persistent intake of high-dose vitamin C is required. This might not go so well with the rest of your body. Yes, vitamin C is a water-soluble vitamin so most of it is peed out but you will get an overdose effect such as nausea and diarrhea; it is not completely harmless to overdose even on water-soluble vitamins over an extended period of time.

Vitamin C supplementation did not affect the incidence of colds. This means that taking vitamin C daily will not affect how often you get a cold, it will just reduce your average cold length by 8 %, mere hours.

Interestingly is also that when the meta-analysis people analyzed the therapeutic trials on their own there were no effects whatsoever on cold duration or severity.

Considering the relatively narrow span of 3-12 % in cold length reduction for adults, there seems to be quite little individual variation. Therefore it is unlikely people react very differently and show a stronger response to this treatment.

Can vitamin C cure a cold?

My humble advice

If you have a persistent bastard of a cold, by all means, take vitamin C if you like but it has to be high dosage for it to work and you have to take it daily over a longer period of time. However, it might really be a waste of money and health in the long run. Eat your fruits and veg instead; these contain all sorts of other things your body needs like little accessory compounds that help vitamins to be utilized and absorbed by the body.

Sleep, drink water and have a whisky (that’s a legend to believe in!).

Sci Hard!
Doctor Anna
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Hemilä H1, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013 Jan 31;1:CD000980. doi: 10.1002/14651858.CD000980.pub4.


  1. Excellent summary of most of the current literature!

    However, it’s not enough to look at metanalyses of clinical or correlative studies. There must also be an examination of the proposed mechanism of action as well (the causation behind the correlation).

    For Vit C… those hypotheses have always been weak and poorly tested. There is no established mechanism of action for EXCESS ascorbic acid to affect viral reproduction or immune response (it’s irrelevant to note what the LACK of ascorbic acid does; scurvy is another thing entirely 🙂 ).

    Bottom line? No, there is zero point to pumping yourself full of vit C.

    Anyone thinking it would work would be far better off focusing their efforts on honing their critical thinking skills instead.

    • Thank you! Yes, I agree with your comments. I too have never seen a reasonable explanation on the proposed mechanism of excess ascorbic acid on the immune system.

      Thank you for commenting!
      Sci Hard!
      – Doctor Anna

  2. This is just another brain washing piece of propaganda from someone who never even try it and trying to be an expert. Most studies are joke because they are sponsored by people/pharma who have no interest to really prove that something works actually the opposite. It is a typical trick since I can set up the study and studies so they fail it or prove it. I always say seeing is believing and I have been taking vitamin C in higher doses than any of those so called studies tested and I know that i got results to say that vitamin C can and will stop cold flu and more. You want prove ? Seeing is believing

    • Dear Miro,

      You are making many assumptions in this comment.
      Firstly, how do you know that these studies are financed by “Big Pharma”, as you call it? Can you please, pick out the ones included in the meta-study I am mentioning and show them to me? I will absolutely change the conclusion my article if you provide some relevant evidence.
      Also, who is “Big Pharma” and why would they hinder the treatment of the common cold? If I were “Big Pharma”, the first thing I would do is to sell vitamin C as tablets and suggest to people to take them. I would make sure that a lot of people think that these tables really work against the cold. That would bring in a lot of money. Oh, hang on…that’s exactly what is happening. A lot of health stores as well as pharmaceutical companies DO sell vitamin C tablets and claim they work…

      If you are going to make claims regarding the flow of money, at least get it right.

      Seeing is not believing. I ensure you that. Controlled experimentation and measurements combined with well-executed statistics is believing.

      Best regards and Sci Hard!
      – Doctor Anna

  3. I’ve been taking vitamin C supplements daily for years… and I’ve no idea if it has any effect on anything other than supplementing my bad nutritional habits (white rice, tuna or herring, green apples, Raisin Bran, whey powder, and currently too much eating out!) along with full spectrum vitamins. Mainly, I take vitamin C to compensate not eating citrus in an area of the world where the winters are long, cold and harsh.

  4. I read somewhere ages ago that a clove of garlic up the bum at the 1st signs of a cold was the thing to do. So I tried it. Still got a cold, but hey… got to experiment. I still practice this ‘treatment’ as its actually rather nice..high absorption.


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