Show of hands how many times you have been told to load up on vitamin C when you’ve been feeling a bit run down with a cold or the flu? I’m sure many – if not all of you.
Vitamin C has been proposed for treating respiratory infections since it was isolated all the way back in the 1930s. However, it became very popular in the 1970’s when Nobel prize winner Dr. Linus Pauling claimed claimed that taking large doses of vitamin C helps prevent and treat the common cold.
What does Vitamin C actually do?
Okay, basics first.
Vitamin C is a water soluble vitamin that acts as an antioxidant and has a role in most aspects of the immune system (i.e. your defence system). High concentrations are found in white blood cells (blood cells which fight infection) and low levels in the blood are associated with reduced immunity (1). Therefore topping up our white blood cells during times of infection with vitamin C seems like a smart idea.
..But what does the evidence say?
Incidence* of colds
A systematic cochrane review in 2013 pooled together 29 trials, with a total of 11,306 participants, and concluded that Vitamin C supplementation does not reduce the incidence of common colds in the general population (2). However there is some evidence that vitamin C supplementation decreases the incidence of colds in special conditions/certain population groups (i.e. those undergoing intense physical stress, such as marathon training) (2).
[*Incidence: The rate of new (or newly diagnosed) cases of the disease.]
Duration and severity of colds
Okay, taking a vitamin C supplement may not stop you from catching a cold but can it reduce the length of time you have it?
First of all – for clarity – in studies looking at the effect of Vitamin C on the duration and severity of colds, “regular supplementation” means that vitamin C was administered each day over the whole study period and “therapeutic vitamin C” means that administration was started only after the onset of symptoms (3)
In the same cochrane review described above, regular supplementation at doses >1g/day, reduced the duration of colds by 8% in adults and 18% in children (2). Mean Duration of the common cold is about a week, so you might save about half a day. Vitamin C also significantly reduced the severity of the colds (2). Severity was measured by ‘;days confined to home’/’days off work or school’ or by a symptom severity score.
Therapeutic supplementation (i.e. vitamin C given after the cold started) trials showed no consistent benefit to vitamin C vs. a placebo (1).
So in summary…
Vitamin C supplementation does not prevent colds in the general population, there is some evidence that if taken regularly, it may reduce the duration and severity of the common cold.
When it comes to nutritional supplements, I generally have the same point-of-view, FOOD FIRST. That is – if you can get it through your diet, and you have no issues absorbing the nutrient(s), then it is unlikely that you need to supplement. Of course there are exceptions to the rule (see below) but for the majority of ‘otherwise healthy’ individuals, a balanced diet should in theory provide you with all the nutrients you need.
Read my Do I need a supplement? article for more information.
So what can you do to prevent getting a cold this winter?
- Eat a balanced diet and aim to hit your 5-a-day: getting enough vitamin C (40mg/day for adults) is typically not an issue for most people – foods like citrus fruits, peppers, broccoli, strawberries, and potatoes contain vitamin c.
- Get your flu jab if you’re an “at risk” individual: read Ciara’s article here for more on that.
- Consider a vitamin D supplement: this is a big exception to the food first rule as Vitamin D is particularly diet alone and is made mostly in our skin following exposure to the sun. Therefore here in the UK, advice from Public Health England (PHE) is that all adults and children over the age of 1 should be taking a 10 microgram supplement of vitamin D each day throughout the autumn and winter months. Certain groups of people are recommended to take it all year.
- Exercise regularly: while intense training sessions such as competitions can cause a transient dip in immunity, regular, moderate intensity exercise can help support your immune system and reduce inflammation (4)
- Get enough sleep: while more sleep won’t necessarily prevent you from getting sick, sleep deprivation can affect your immune system and make you more susceptible to catching a cold or the flu (5)
- Stop smoking: smoking (including passive smoking) can impair the defence system of the airways, increasing the risk of coughs, colds and chest infections (6,7). For advice and support, check out the STOPTOBER website page.
Geissler, C. and Powers, H.J. Human nutrition (13th ed.) Oxford: Oxford University Press; 2017
Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane database of systematic reviews. 2013(1).
Hemilä H. Vitamin C and infections. Nutrients. 2017 Apr;9(4):339.
Nieman DC, Wentz LM. The compelling link between physical activity and the body’s defense system. Journal of sport and health science. 2019 May 1;8(3):201-17.
Prather AA, Janicki-Deverts D, Hall MH, Cohen S. Behaviorally assessed sleep and susceptibility to the common cold. Sleep. 2015 Sep 1;38(9):1353-9.
Feldman C, Anderson R. Cigarette smoking and mechanisms of susceptibility to infections of the respiratory tract and other organ systems. Journal of Infection. 2013 Sep 1;67(3):169-84.
Zhou G, Liu H, He M, Yue M, Gong P, Wu F, Li X, Pang Y, Yang X, Ma J, Liu M. Smoking, leisure-time exercise and frequency of self-reported common cold among the general population in northeastern China: a cross-sectional study. BMC public health. 2018 Dec;18(1):294
feature image: stephanie-harvey via Unsplash