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Monday’s medical myth: drink plenty of fluids when you have a cold

When you’re sick with a cold, you’re likely to be told to rest and drink plenty of fluids – water, juice, tea and the old favourite, chicken soup. This has been the prevailing advice for generations and…

Drinking extra fluids when you’re sick might do more harm than good. Jason Rogers

When you’re sick with a cold, you’re likely to be told to rest and drink plenty of fluids – water, juice, tea and the old favourite, chicken soup.

This has been the prevailing advice for generations and seems to be intuitively sensible. With an upper respiratory viral infection, you secrete more fluid from the nose and may be running a fever, which could result in additional fluid loss. Your appetite may also be decreased.

When considering treatment for colds, we first need to work out the desired outcome. Shortening the illness, or, perhaps making the symptoms less severe, would get most people’s vote.

Having established the desired outcome, it wouldn’t be hard to set up a trial of people with coughs and colds, where half the group was urged to drink extra fluid and the other half allowed to drink simply when thirsty.

If the trial was set up fairly, and there were enough participants, we would have empirical information about whether drinking extra fluids was effective.

I was part of a small team that searched medical journals electronically for any such trials. What did we find? No one seems to have bothered to conduct the trials. Or if they have, they haven’t published them.

I could finish off here with some comment about it being a pity this hasn’t been studied properly, and the irresponsibility of folk who go around offering a treatment for which there is no evidence, (both of which I believe, incidentally).

But there is a small postscript. In our search for evidence we stumbled across some medical journal articles called “case series”, which outline unusual events that doctors think tell a lesson, or spark a research question.

The doctors describe how series of individual children they treated came to harm after being given extra fluids for what was initially considered a trivial cold (or upper respiratory infection).

Usually, the infection turned out to be more severe than initially anticipated. The children then suffered something called cerebral oedema, which is extra fluid in the brain. This can cause convulsions and brain damage because of the restricted space inside the skull, and can even lead to death.

The doctors writing these case series weren’t sure what had caused the cerebral oedemas. It might have been some effect of the infection, of course. But the doctors all suggested it might have simply been the extra fluids the patients were given – sometimes by the medicos themselves (by intravenous drips in a few cases).

This could be the result of the body secreting Anti-Diuretic Hormone, which temporarily shuts off our kidneys from excreting urine. This occurs in times of severe stress. Anti-Diuretic Hormone probably evolved in order to protect us mammals from dying of fluid loss when wounded or very ill.

But it might prove fatal if a person with a severe infection was persuaded to drink fluids they didn’t need (above that dictated by their thirst) and, at the same time, started secreting Anti-Diuretic Hormone.

Right now, this is all speculation. We don’t really know. But until we do, perhaps we should stop exhorting our sniffly kids to “drink more fluids” because they have a respiratory virus.

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8 Comments sorted by

  1. Douglas Cotton

    B.Sc.(Physics), B.A.(Econ), Dip.Bus.Admin

    Another myth about colds is that cold weather causes them. The reason there are more in winter is almost certainly the fact that people get less vitamin D from the sun. In general, high dose vitamin C taken at least every 6 hours, together with up to 5,000 IU of vitamin D3 and a zinc supplement will shorten the duration and severity of a common cold.

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

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

      In reply to Douglas Cotton


      In traditional Chinese medicine cold weather or 'cold meteorological Qi' (han Qi ) is the external environmental factor that brings about 'warm factor epidemic' or 'wen bing'. And the signs and symptoms of warm factor disorder or wenbing' is very similar to common colds or influenza. Viewed from this perspective, the statement that 'colds are brought about by cold weather' is not a myth.

  2. Daniel Reeders

    logged in via Facebook

    I am surprised by this article. This is exactly how panics get started. A tabloid newspaper in a multinational news conglomerate that heavily syndicates its own articles could pick this up tomorrow and say "Professor of Public Health warns against giving children fluids when sick". We know that a case series barely makes it onto the hierarchy of evidence sources, but to the general public it falls under "research shows...". And did anybody check whether the risk identified in the case series is more common than the risk of dehydration in sick infants?

  3. Rosemary Stanton

    Nutritionist & Visiting Fellow at UNSW Australia


    The reference you cite is only for zinc, not for vitamins C and D (which readers might have inferred from the way you worded your statement).

    Evidence that vitamin C is helpful is scanty indeed. A review of all studies finds (small) advantages only for skiers, marathoners, male (not female swimmers) and army personnel exercising in sub-Arctic temperatures. For others, placebo-controlled trials do not support taking vitamin C during a cold.

    We also lack evidence for vitamin D and colds…

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    1. Doug Cotton


      In reply to Rosemary Stanton

      We meet again Rosemary. Your reference to the Life Extension Foundation does not quite paint the full picture. As a non-profit organisation they do not sell supplements for profit. They do so because no one else formulates such potent products. I defy you to find a better antioxidant mix than their main product Life Extension Mix which I have been taking for nearly 20 years along with many other state-of-the-art formulations - (Remember?)

      I think the reference…

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    2. Rosemary Stanton

      Nutritionist & Visiting Fellow at UNSW Australia

      In reply to Doug Cotton


      I previously objected to the implication that your reference referred to vitamins C and D when it actually referred to zinc supplements. Sending a reference to 460 abstracts on vitamin C hardly addressed the topic of this Conversation, which was the common cold. I did go down the list until I found one reference on vitamin C and the common cold, so I looked up the paper (from the Herbal Health Centre in East Sussex) and found its statistics faulty. When the confidence intervals for the data…

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    3. Doug Cotton


      In reply to Rosemary Stanton

      And here's a paper in the British Journal of Nutrition 1992 ..

      "vitamin C has consistently decreased the duration of cold episodes and the severity of symptoms."

      P.S. Being a member, I can assure you Life Extension Foundation Members do not participate in any profit sharing. There is a reduction of 25% in prices for members (encouraging membership) and further savings for purchasing four (4) at a time of any item - reflecting reduced handling costs I presume. They also have an annual 10% off sale to clear stock. In my opinion, their member prices are less than Australian health food store prices for anything that comes anywhere near the quality. You have to compare likes with likes. And of course they have numerous products that you can't buy in Australia, but can import from them (ex Fiji) for your own use. Some of these products actually slow the aging process as I know from personal (albeit anecdotal) experience.