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Monday’s medical myth: vitamin C prevents colds

Vitamin C is so often suggested as a treatment for the common cold that it’s almost considered common sense. This well-known vitamin is primarily found in fruits and vegetables, with small quantities in…

A vitamin C a day won’t keep colds away. Owaief

Vitamin C is so often suggested as a treatment for the common cold that it’s almost considered common sense. This well-known vitamin is primarily found in fruits and vegetables, with small quantities in some meats.

With a healthy diet, most of us should get all the vitamin C we need from food. But this doesn’t stop many Australians boosting their intake through vitamin supplements.

A story on vitamin C should start with scurvy. The other name for vitamin C is ascorbic acid, which literally means “anti-scurvy”. As vitamin C is required to build and repair body tissue, its deficiency leads to a range of horrible symptoms including bruising, bleeding, loose teeth and poor wound healing.

Scurvy was a leading cause of death among 18th century sailors. A. Oostendorp

Until the modern era, scurvy was a major cause of death in those without access to fresh food, particularly sailors on long sea-voyages and medieval city dwellers.

The history of vitamin C tells an important story about science in medicine - and informs us about three key elements of medical research:

1. Treatments need to be tested in clinical trials

The first (documented) clinical trial of a medical treatment was by Scottish Royal Navy physician James Lind in 1747. He divided sailors suffering from scurvy into different treatment groups and found the sailors who received oranges and lemons made a drastic recovery.

Although fresh citrus fruits had been reported as effective for scurvy prior to Lind’s study, it had never been tested systematically. At that time, it was but one of many purported treatments (most of which we now know to be useless). Lind had demonstrated an unambiguously effective treatment for a potentially deadly condition.

2. Medical practice needs to be informed by new research

The medical establishment in the 1700s rejected Lind’s findings. The prevailing view was that scurvy was related to spoiled food and hygiene. As this was an age where clinical trials weren’t the norm, no one replicated the findings.

It wasn’t until four decades later that another Scottish Navy Physician, Gilbert Blane, instituted health reforms and mandated the use of lemon juice.

3. Assumptions without empirical confirmation are risky

Unfortunately, scurvy was far from conquered. Fresh citrus fruits were impractical on long sea-voyages so juice and concentrates were carried instead.

In the late-1800s, a change in the preserving process and a switch to limes resulted in a juice that was devoid of any vitamin C content – useless for preventing scurvy. It was wrongly assumed that it was the “acidity” that mattered. The lack of therapeutic testing contributed to the disastrous 1911 Scott expedition to the South Pole. The team members were beset with scurvy, 150 years after Lind’s experiment.

Scurvy was finally identified as a nutritional deficiency in the early 1900s, and by the 1930s, vitamin C was found be the essential nutrient involved.

Moving forward a few decades, the belief of the effectiveness of vitamin C for colds gained momentum following the publication of Vitamin C and the common cold by esteemed chemist Linus Pauling (one of the few people to have won more than one Nobel Prize). Pauling extensively promoted vitamin C as having a wide range of health benefits and took large regular doses of supplements.

But like the history of citrus and scurvy, it’s not enough to simply claim reasons why something should work. Assumptions are risky and treatments need to be tested. So what does the research evidence actually show?

Vitamin C supplements won’t treat or prevent colds. Kokopinto

When used as a treatment for cold symptoms in the general population, vitamin C supplements appear to do no better than a placebo, even in large doses (greater than one gram a day).

If you take vitamin C supplements every day for prevention, you still won’t avoid any colds. But the symptoms may be milder and the duration of symptoms slightly reduced – about half a day for a typical cold lasting a week.

It’s important to remember that we don’t know if regular high-dose vitamin C supplements are entirely safe when taken over the long-term. There is some evidence to suggest they aren’t.

We all become afflicted by the common cold at times and it would be wonderful if something as simple as vitamin C supplements made a meaningful difference. But unfortunately, as the saying goes, many a beautiful theory has run aground on awkward fact.

Even taking the most favourable interpretation of the evidence, vitamin C supplements have only a minor effect on symptoms – and that’s only if they’re taken every day.

Join the conversation

24 Comments sorted by

  1. Russell Hamilton


    From the abstract of the article cited:

    "One large trial with adults reported equivocal benefit from an 8 g therapeutic dose at the onset of symptoms, and two trials using five-day supplementation reported benefit. More trials are necessary to settle the possible role of therapeutic vitamin C, meaning administration immediately after the onset of symptoms"

    So there were some benefits, and 'more trials necessary'.

    I was perlexed at the 'Objectives' of the study: "To discover whether oral doses of 0.2 g per day or more of vitamin C reduce the incidence ...."
    Who takes 0.2g per day of vitamin C to stop a cold? I'm in the 8g a day category and it works for me. Might not work for the general population, but thankfully I'm one of the lucky ones, for whom it does work.

    1. Russell Hamilton


      In reply to Dave Smith

      No, but I have, over the decades, tried a very few of the most popular 'natural cures', and found by trying it that large, continuous doses of vitamin c, as soon as you feel a cold coming on (sore throat etc) stops the cold, or its symptoms. It's the only natural cure that I've found to work like that, the only one I would recommend to people - though it may not work for them like it does for me.

      I've been in places where I didn't have vit c and have had to endure a cold. Ian Musgrave would…

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    2. Sue Ieraci

      Public hospital clinician

      In reply to Russell Hamilton

      I have often felt a cold coming, done nothing, and woken up the next morning to find that the cold hadn't developed. Much cheaper than vitamin supplements.

  2. Stephen Lehocz
    Stephen Lehocz is a Friend of The Conversation.

    Interested public.

    Interesting article Michael. But aren't you being a little disingenuous?

    Also from the Cochrane Library is this conclusion:

    RESULTS: Overall, reported flu and cold symptoms in the test group decreased 85% compared with the control group after the administration of megadose Vitamin C.

    CONCLUSION: Vitamin C in megadoses administered before or after the appearance of cold and flu symptoms relieved and prevented the symptoms in the test population compared with the control group.

    Here is…

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    1. Michael Tam

      General Practitioner, and Conjoint Senior Lecturer at UNSW Australia

      In reply to Stephen Lehocz

      Stephen, you linked to a single study. The article I used above is the systematic review performed by the Cochrane Collaboration for this question. That is, it is a process of identifying ALL the research relevant to this question and using statistical techniques to combine the data. The aim of doing such an exercise is to improve the precision and reliability of the conclusions that we can draw.

    2. Stephen Lehocz
      Stephen Lehocz is a Friend of The Conversation.

      Interested public.

      In reply to Michael Tam

      That's irrelevant. There were marked improvements, showing that vitamin C had a large impact on a cold. That's my point - vitamin C does have a marked affect on a cold.

      Where your article was implying that there are none to no effect on a cold. That's what I'm disputing.

    3. Shane Kidd

      logged in via LinkedIn

      In reply to Stephen Lehocz

      To look at the "scientific medical system" for facts about vitamin C is akin to asking the Defense Department what they know about compassion.

      People, not scientists, have known the benefits of mega-doses of Vit C and any other vitamin and mineral for good health for over a century.

      Why we even bother to quote or listen to a propaganda machine that is at this moment attempting to have "vitamins" taken off the shelf is beyond me. See studies in the UK, US and Australia.

      If you want the facts, look at studies done before the 1930's, as the drug companies didn't have a stranglehold on the processes and results, as they do now.

    4. Paul Goodsell

      Eco-Warrior / Business Owner

      In reply to Shane Kidd

      A propaganda machine, aye? Can't the same be said of the vitamin supplement industry? It's an industry worth many billions of dollars. Haven't they got something to protect too?

    5. Shane Kidd

      logged in via LinkedIn

      In reply to Paul Goodsell

      Paul, in reality, yes, the vitamin industry is as corrupt and biased as the pharmaceutical industry. Both have their own drums to beat.

      I don't prescribe to either, preferring to obtain my vitamins and minerals and life-forces from the original source ... food.

      Nutrition, health and wellbeing is simple. Eat food. (that doesn't include anything made in a factory)

    6. Jon Ford

      Leader of the Low Back Research Group at La Trobe University

      In reply to Shane Kidd

      Wow! I only joined today and am very excited about The Conversation. I'll delve straight in.

      Interesting that much of the commentary above fails to acknowledge
      - The limitations of systematic reviews in complex disease
      - The importance of not ignoring clinical trials with a large effect in complex disease when constructing clinical guidelines
      - The fact that even academics enjoy promoting unsubstantiated conspiracy theories

  3. Cris Kerr

    Volunteer Advocate for the value of Patient Testimony & Sustaining our Public Healthcare Systems

    My personal experience is that Vitamin C has been very effective in
    lessening symptoms and duration when taken in periodic daily doses of 3 to
    4 times a day - not through extended-release versions, and not via a single
    large daily dose due to Vit C being water soluble: These and other variable
    factors should be taken into account yet often aren't, and so we will continue
    to see mixed results.

    On the plus side... large dose vitamin D supplementation has been promoted
    to patient chat…

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  4. Rey Tiquia
    Rey Tiquia is a Friend of The Conversation.

    Honorary Fellow, School of Historical and Philosophical Studies at University of Melbourne

    Dear Michael,

    Thank you very much for citing the James Lind clinical experiment the sigmificance of which lies on two counts :

    1. That scurvy like the common colds are both preventable as Dr. C. P. Stewart, Professor of Clinical Chemistry at the University of Edinburgh iin the article by Anthony Lorenz that you cited as well, said :

    "This 'experiment,' the first carefully controlled therapeutic test in medical history, proved beyond doubt the efficacy of lemons and oranges and the relative…

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    1. Citizen SG


      In reply to Rey Tiquia

      I agree the james lind scurvy trial is a very interesting topic. interesting because it had a control group and interesting because the correlation that was found was not between vitamin c and prevention of scurvy but ingestion of fruit and prevention of scurvy. As the article has pointed out it was not until the development of modern chemical method that the causative chemical (Vitamin C) was isolated.
      James Lind's trial might be 'holistic' but it couldn't determine what the causative agent…

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    2. Michael Tam

      General Practitioner, and Conjoint Senior Lecturer at UNSW Australia

      In reply to Citizen SG

      This article is somewhat constrained by its scope "medical myths", but James Lind's trial methodology would be considered rather low quality today. It consisted of only 12 patients (sailors suffering from scurvy) with only 2 patients in each treatment group.

      However, Lind serendipitously studied a condition where a simple treatment had rapid and dramatic effects, and had chosen other treatments that basically had none. "All or none" is still strong evidence, though the results may have been…

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  5. Roger Carter


    Articles this biased bring the Conversation into disrepute. As several correspondents point out, the latest Cochrane review does NOT support the author's contention that "We all become afflicted by the common cold at times and it would be wonderful if something as simple as vitamin C supplements made a meaningful difference. But unfortunately, as the saying goes, many a beautiful theory has run aground on awkward fact." No one is claiming that Vit C "cures" a cold, but the review clearly supports…

    Read more
    1. Roger Carter


      In reply to Roger Carter

      Oh and in addition ... those of you who have access should read the lively follow up to the Cocharne Review in question here:
      One of the correspondents (Hemila) makes this comment:
      "Thus, there seems to be a justification to test therapeutic vitamin C at the individual level for children who have problems with respiratory infections, because there is strong evidence that vitamin C differs from placebo, it is inexpensive and safe and, unlike the antibiotics, it does not cause harms on microbial ecology.". Note the phrase "strong evidence" !

    2. Michael Tam

      General Practitioner, and Conjoint Senior Lecturer at UNSW Australia

      In reply to Roger Carter

      Roger, I suggest that you actually read the Cochrane review again, and not just the summary. Hemila, who has an extensive research career in vitamin C, basically agrees with my conclusion - which is the conclusion of the review!

      I agree that something interesting happens to those "exposed to short periods of extreme physical stress". That is a very unusual context and of little relevance to the general community. Indeed, I wrote, "When used as a treatment for cold symptoms in the general population…

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  6. Eddy Schmid


    I'm 62 years of age, and have not had a flu or serious cold for 20 years, despite grand children, sons and daughters, as well as my wife,(who regularly gets her FLU shot annualy) coughing and weezing regularly around me.
    Now I could say I'm totaly impervious to colds, but that wouldn't be accurate, I do on occassion get slight symptoms of a coming cold or flu, as soon as the signs become identifiable, I increase my daily intake of vitamin C from 1,000 milligrams to 2,000 milligrams.
    Within 24 hrs…

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    1. Sue Ieraci

      Public hospital clinician

      In reply to Eddy Schmid

      Why bother having research or health professionals at all when we can just ask Eddy for his considered opinion?

      It is typical for tonsillitis to be common during childhood (it is part of the front-line immune system) and then become less common with time - antibiotics or not. The same thing happened to me.

      I also rarely get severe colds, and can't remember last time I had 'flu, but I don't take Vit C (except in foods). My anecdote neutralises your anedote. That's why we need research.

    2. Russell Hamilton


      In reply to Sue Ieraci

      In this case one anecdote doesn't necessarily 'neutralise' another - they could both be true. It would be good if you were curious enough to want to find out why, rather than fall back on the lazy answer "because they're fools".

      And when you do your research, it would be good to research what people actually do, if that's what your looking to find out about.

    3. Roger Crook

      Retired agribusiness manager & farmer

      In reply to Sue Ieraci

      Sue, why do you have to be so rude to a non health professional like Eddy? I hope this isn't an example of the view of many 'health professionals' that 'we know best'.
      Cos, madam, over the years, that has been shown to be just not true.
      Doctors who listen to their patients are becoming a rarity as they progressively follow the example set by lawyers, where fee paying hours are the mantra and each hour is broken to to 6 min units or patients/hour.
      What does concern me is what appears to be the ever-increasing, I would say arrogant view, among scientists that on so many subjects, 'the science is settled',