Vitamin C - efficacy, misconceptions and myths

In my experience there is no vitamin more misunderstood that Vitamin C in terms of its efficacy, functionality and sources.    

Vitamin C is a water-soluble vitamin.  This means it is not stored in the body in the way fat soluble vitamins are (vitamin A for example).  It does not ‘build up’ in the body (in the way anti-inflammatories do) and any excess will simply be excreted in urine.  We cannot synthesize the nutrient endogenously – therefore daily intake is essential for optimal health.

Dose

There is discrepancy regarding the optimal dose of vitamin C.  The UK RDI for adults 19-64 is surprisingly low – 40mg a day.  To put this into perspective an average 100g orange contains around 50mg of vitamin C.  The Australian NRVs set the level at a similar amount – 45mg/day. 

There is argument that the RDI is set too low and should be adjusted.  This is because the amount set is the amount needed to prevent the onset of scurvy – a disease caused by vitamin C deficiency – but not necessarily the daily amount for optimal physiological functioning.   Amounts closer to 900-100mg daily have been recommended.

It should be noted that certain groups may have higher vitamin C requirements.  These include: smokers, people with malabsorption issues and those with certain chronic diseases. Young people and the elderly may also have different needs - but these are reflected in the RDI values.

Immune Health

 Vitamin C is an often-used remedy for both prevention and treatment of the common cold.  We all have experienced the advice to ‘drink some orange juice’ or ‘take some vitamin C’ when we start showing symptoms of a common cold.  But is there any evidence to support this?  Recent studies have suggested that the efficacy may be overstated.

A recent review suggests that increased intakes of vitamin C (200mg/day) do not reduce the incidence of the common cold within the general population.   

Higher intakes may be beneficial under certain conditions however.  These can include those undergoing extreme physical exercise, those exposed to very cold environments and those who may have low vitamin C absorption rates (eg. Elderly people and smokers).

The use of vitamin C may modestly shorten the duration of a cold (by around 8%) but taking vitamin C after the onset of symptoms does not, at this point, appear to confer any benefit.

There is some evidence of the efficacy of vitamin C in treating respiratory infections specifically.  This 2017 review found that vitamin C appears to be able to both prevent and treat respiratory and systemic infections if doses are high enough (around 100-200mg).

However don’t guzzle down an entire bottle of little orange pills at this point.   As this paper points out most of the benefit incurred is due to an avoidance of deficiency.  Cases where higher doses enhanced immune functioning tended to be limited to those involving some sort of physical strain (as mentioned above).  The paper concluded: “With regard to the therapy of the common cold the application of vitamin C alone is without clinical effects.”

Side Effects

Common side effects of too much vitamin C tend to be relatively minor and circle around digestive issues including:

-       Stomach pain

-       flatulence

-       Diarrhoea

Fortunately, these only tend to be experienced in response to supplementation of vitamin C and rarely seen through dietary consumption.

Sources of Vitamin C

Another area where vitamin C is misunderstood.  We all know about citrus fruits (oranges etc) being sources of vitamin C.  But did you know the following all contain high levels of vitamin C – in many cases more than oranges:

-       Peppers

-       Broccoli

-       Kiwi fruit

-       Pineapple

-       Cauliflower

-       Kale

-       Brussels sprouts

-       Strawberries

-       Red cabbage

-       Blackcurrants

What to do?

If you are eating a healthy, balanced diet you are extremely unlikely to be deficient in vitamin C – at least according to the current RDI.   The best bet is to eat according to the eatwell guide consuming plenty of fruits and vegetables, paying particular attention to those listed above

If you are involved in strenuous, regular physical exercise or are in one of the groups with higher requirements mentioned above there may be some benefit to considering supplementation – but do not exceed an upper limit of 1000-2000mg/day.

Feed the life you want to lead,

Duncan