Does vitamin C really help against a cold?

Today the dictator of The Imaginarium has come down with a particularly annoying form of man-flu. I am not certain why this is, and despite being a woman, I still get terrible man-flu.

What to do?

I immediately received good advice from various people and well-wishers (thank you). What most people told me was: sleep, drink water, and take vitamin C. I understand the sleeping and the drinking water part but what about vitamin C (ascorbic acid in science-lingo)? What is the truth behind this old claim for beating colds and the flu? Is it placebo or does it really work?

Some Scandinavian friends also suggested that I should drink a large glass of whiskey but since it is 9 a.m., I think I will pass on that one for now. NB: Irish friends suggested warm whiskey with lemon (vitamin C again) and honey. Though even this sweeter version does not seem appropriate at 9 a.m.

Whiskey - good stuff! (Image credit: "Redbreast15")

Whiskey – good stuff! (Image credit: “Redbreast15“)

Does vitamin C really help against a cold?

This simple question turned out to be more difficult to answer than I had anticipated. This is one of the reasons why I have strayed away from human biology: one cannot do proper experiments. It is not like one can shut people in a room for a month and control every step they take and compare them with a group that one treated differently; or kill and dissect them for that matter.

Messy, messy statistics…

There are so many variables involved with testing the efficacy of vitamin C that the statistics become messy and well, very messy. Due to this difficulty one needs to include a very large number of participants for the study to hold statistically. I was struck by the low number of participants in some of these studies. I understand that 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). OK enough statistical ranting and back to the ascorbic acid.

By Jason Rogers [CC BY 2.0 (], via Wikimedia Commons

Man-flu. (Image credit: Jason Rogers)

Another urban legend debunked

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 data-bases, 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. Hail to the great God(s) of massive computer power! This means that all of these little studies are 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. This study included only 12 patients that had already had shown symptoms of autism. Such studies should not be included in a meta-analysis. They are bad and can cause a lot of harm.

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 diarrhoea; it is not completely harmless to overdose even on water-soluble vitamins over an extended period of time.

Vitamin C supplementation did not effect 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) and somewhat lessen the severity of it.


The Florida Navel Orange. (Image credit: Benjamin D. Esham)

Interestingly is also that when the meta-analysis people analysed 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 not very likely that some larger groups react very differently and show a stronger response to this treatment.

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 whiskey (lemon and honey are optional)(?!)

Science Safely! terribly, terribly sick right now.

…is terribly, terribly sick right now.

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.

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