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ANALYSIS: Can vitamin C really prevent or cure a cold?

We’re often told that there is no cure for any of the multitude of viruses behind the shared symptoms which make up the common cold. Yet a big segment of the pharmaceutical market caters for exasperated individuals eager to get back on their feet as fast as possible.

Although compositions vary, most remedies contain vitamin C as an ingredient. Is there any evidence to support its use in fighting off a cold?

To vitamin C or not to vitamin C?

Two publications, writing recently about this issue, reached the exact opposite conclusion.

Huffington Post SA, citing (pre-2016) summaries from the United States’ National Institute of Health, wrote that a high dose vitamin C is unlikely to do much to prevent or treat a cold. And, what’s worse, it only puts you at risk of possible side-effects such as diarrhoea, nausea, kidney stones or even excessive dietary iron absorption when used regularly.

Men’s Health, on the other hand, reported on a review of 24 studies between 1972 and 2002 by the University of Helsinki and published in January this year. Their finding: The key to using vitamin C to help you fight off a cold is very high doses.

By very high doses, they mean in the order of 6-8 g. By comparison, the recommended quantity needed daily - by way of diet - to remain healthy is probably slightly less than 0.1 g.

There is a condition for this theory, however. The review paper found that even high doses will likely only help prevent a cold when someone is exposed to extreme environments, like marathon runners or military personnel in cold-weather training.

Despite the lack of preventative power in general, there may still be something to say for vitamin C’s ability to reduce the duration of a cold, though.

Understandably, this leaves regular folk in a predicament. Should I spend money on vitamin C supplements to help fight a cold, or not? Let’s take a look at the evidence.

Human bodies unable to make vitamin C

Let’s start off with the basics. Vitamin C, or ascorbic acid, is an essential nutrient, which is to say that we have to get it from our diet, as our bodies are unable to make it.

This vitamin plays a vital role in a multitude of the chemical reactions in our body, particularly in many of the reactions that eventually form the structural proteins of our skin, blood vessels and internal tissues. It therefore has a direct role in growing, healing and general cell maintenance.

People also may be familiar with its role as an antioxidant, helping to lessen the burden of free radicals that build up in our bodies as a result of cellular processes.

Effect studied since the 1940’s

These facts make a good argument for why vitamin C is an essential nutrient, but what does it have to do with our immune systems? Research is gradually shedding light on this question.

Vitamin C has been shown to play a role in the production of various components of the immune system. A Harvard study suggests that vitamin C might be involved in the very mobility of the individual cells that make up our immune system.

The research community has been looking at the effect of vitamin C on the common cold since the 1940’s. But it was only in 1970 when chemistry Nobel prize winner Linus Pauling started exulting vitamin C, that the number of publications exploded. Still, a firm conclusion remained murky as many papers reported contradictory results.

This kind of uncertainty is something that researchers have to deal with on a regular basis. As such, tools have been developed to sort through the large amount of noise in any field, including meta-analyses.

When conducting a meta-analysis, researchers examine the findings of multiple research studies using specialised analytic tools as if they were one large study. This process more accurately reflects the reality of the phenomenon being examined than any of the individual studies.

The Cochrane organisation maintains meta-analyses of vitamin C studies,  spanning nearly 50 years worth of research, and we’ll be looking at their 2013 review for guidance.

How it affects frequency, duration & severity of colds



We can approach the effect of vitamin C on the common cold from many angles. The first is how it affects how often you catch a cold.

The Cochrane review pooled 10,708 people from 24 studies between 1942 and 2002 who took 0.25 - 2 g of vitamin C as a daily supplement, often over the course of a single winter. The researchers found that there was almost no change in the number of distinct episodes of illness. They got the same result when they restricted the study pool to the people who took more than 1 g daily.

But something unexpected happened in 5 studies where the authors examined the effect of vitamin C on people under significant short term stress, namely marathon runners, skiing students and military personnel on sub-arctic operations. Not only did vitamin C supplements taken during the periods of stress reduce the number of colds, it just about halved it.

So while vitamin C probably won’t help the general public catch fewer colds,  what about once you already have the sniffles?


For this part, the Cochrane reviewers examined 17 publications, covering 21 different trials with 7,215 distinct episodes of illness between them. Regular vitamin C supplements did indeed shorten the duration of colds, by 3.7%-12%. For children, the findings were a little more impressive, with colds being 7.3%-21% shorter.

But individual variety may not act in everyone’s favour. For a statistical minority, vitamin C supplements actually increased the duration of their cold.

Here’s the interesting part:  Both the Cochrane review, as well as the review Men’s Health wrote about, found evidence that taking a large dose - around 8g at the very beginning of a cold - is equally, if not more, effective to shorten a cold than chronic supplementation at lower doses.

There is a very narrow window of opportunity, though. If you begin to take vitamin C days into an already established cold, the effects drop to barely different from a sugar pill.


The final point of analysis was the severity of colds. Although there was a small improvement in the severity of symptoms found across most of the studies included, it wasn’t universal and results were modest.

Might be able to shave off a day

In conclusion, if your diet is balanced, taking a daily supplement of vitamin C is unlikely to improve your odds of avoiding a cold.

But if take you a large dose, up to 8 g just as you begin to feel ill, you might be able to shave just under a day or so off the total episode. However, this is subject to large variation between people and everyone reacts differently. Side-effects may even be a possibility.

To minimise the side-effects associated with short bouts of use - mainly diarrhoea - one of the leading researchers on vitamin C recommended to Africa Check to take vitamin C “in as many split doses as you can over the course of a day”. Prof Harri Hemilä from the department of public health at the University of Helsinki said this should be done while the primary cold symptoms last, typically a few days to a week. He advised against the general daily use of vitamin C.

The official Cochrane recommendation is to add vitamin C as soon as a cold is starting to see if it has any effect on you. But once you’re already a number of days into a cold, there isn’t much vitamin C will do for you.

In the end, there is a much cheaper and proven way to prevent the spread of common seasonal viruses: Thoroughly washing your hands with soap and water after coming in contact with sick people or frequently touched surfaces.

Petrie Jansen van Vuuren is a medical student at the University of the Witwatersrand, with a postgraduate background in neuroscience research at the University of Pretoria.

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