It’s such an oft-repeated thing it has become common knowledge: Vitamin C is what we need when we are coming down with a cold or flu.

Many swear it helps them prevent winter ills; others say it eases and erases symptoms and helps them bounce back if they do get struck down. But what is the truth here? Is vitamin C the cold cure and immunity boost we may believe it to be?

Where did this idea come from?

The link between vitamin C and immunity is well established, in the sense that this is an essential vitamin that we need for the proper functioning of our immune system. Vitamin C plays a role in various processes in the body, including the production of white blood cells and antibodies. Having enough vitamin C in our bodies is important for our overall immune function, and our overall health.

This link was discovered way back before anyone had identified or named vitamins as vitamins, when it was found that sailors in the 18th century could recover quickly from scurvy when they ate citrus fruits, which we now know are high in vitamin C (it took until 1933 for the link to be fully understood).

We now know that this vitamin is crucial for collagen synthesis - it helps our skin heal and helps maintain bone, tendons and blood vessels - and it helps us absorb iron from the foods we eat. It is also an antioxidant, protecting cells from damage caused by harmful free radicals, reducing oxidative stress and promoting overall cellular health.

The idea of supplementing with vitamin C probably came from the fact that it is not stored in the body; we need to get it regularly from what we eat and drink in order to keep our levels up. The ‘insurance policy’ thinking that applies to most vitamins comes into play here: if we’re not getting enough from our food, we reason, why not top up with a supplement?

Do vitamin C supplements help us with colds and flu?

We know vitamin C is good for immunity. It is less clear, however, that supplements help with prevention or symptoms of colds and flu. Despite nearly a century of research, the evidence remains pretty mixed.

Taking vitamin C regularly as a supplement does not seem to prevent colds or flu in most people. There is an exception: there have been some studies looking at people under extreme physical stress, such as marathon runners and soldiers in

sub-arctic conditions, where it was found that if the participants started taking vitamin C two to three weeks before their strenuous activities, their risk of developing a cold was reduced by about half.

For those of us who are not sub-arctic soldiers or marathoners, the evidence in large reviews shows that taking vitamin C does not prevent a cold. However, taking it regularly before you get the cold could shorten the amount of time you will be

sick by around 10 percent. So a cold that would have lasted 10 days will be over in nine.

It has also been found that people who always took vitamin C had slightly milder cold symptoms. This seems to be particularly the case for children.

That said, taking vitamin C after your cold symptoms appear probably will not do any good. The evidence shows this does not have any effect on how long you will be ill for.

What about liposomal vitamin C?

Liposomal or lipo-spheric vitamin C seems to be all the rage. It comes with big claims - and a price tag to match. It is a form of vitamin C encapsulated in liposomes (tiny fat-like particles).

There have been some studies looking at the effectiveness of liposomal vitamin C that suggest it appears to be absorbed better by the body. Whether that translates into any cold and flu benefits is not clear. 

Any downsides to taking it?

Taking any vitamin C supplements in very high doses (more than 2000 milligrams a day, which is considered the safe upper limit) can cause diarrhoea and other digestive issues. There is no such risk in the vitamin C you get from food.

The only other downside is really that it is not doing anything, and you are simply excreting any excess in the form of, as nutritionists like to put it, expensive urine.

If not vitamin C… what can I take?

There is no magical thing that will protect us from viral illness (which hopefully we all know by now). But health experts stress that looking after ourselves as well as possible will help our immune system to stay in top shape, so that when we do

get hit with a virus, we can handle it OK.

Nutritionist Nikki Hart is of this view, and cautions against singling out one vitamin as the solution.

“Vitamins, minerals, phytonutrients - they all work to repel oxidative damage”, she explains.

“So you can't just label vitamin C as protective.”

She stresses that the best way to get our vitamins – including vitamin C – is through food. Citrus fruit and other colourful fruits and vegetables are all useful here, and getting lots of those on our plates means we will easily hit the recommended

daily intakes. Hart said food is best not only because it offers a highly bioavailable form of vitamin C, but we also get other goodies, too, like fibre and other vitamins.

She also said we need to remember all the things that boost immunity (and many other things too): physical activity, enough sleep, minimising alcohol and not smoking.

“The immune system is bigger than just vitamins and minerals.”

Lastly, there is one old bit of wisdom that might be true: one study found chicken soup is not only comforting, but it might have anti-inflammatory properties that lessen cold symptoms. 

In other words, spending the supplement money on fresh produce might be a better, and more enjoyable, way of avoiding or treating a cold.