The following article was published on The Conversation.

Monday’s medical myth: vitamin C prevents colds

By Michael Tam, University of New South Wales

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.

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?

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.

Michael Tam does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

This article was originally published at The Conversation.
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