As the early chill of winter begins to seep into morning air, grocery stores and pharmacies launch their campaigns. Their goal? To persuade consumers to arm themselves with vitamin C, a supposed shield against the inevitable cold and flu season.
But how did this widespread belief take root?
The origins of this notion weave a tale that involves a Nobel Prize laureate, a controversial book, and a series of claims that, upon closer inspection, don’t entirely hold up.
Nobel Prize winner writes a book
Enter Linus Pauling, a distinguished American chemist, celebrated with two Nobel Prizes. In 1954, he garnered the award in chemistry for his pioneering work on chemical bonds, and by 1962, he had earned another, this time for peace, recognizing his fervent opposition to nuclear weapons testing.
Though his expertise lay far from nutrition or virology, Pauling ventured into these realms with the publication of a book in 1970, exploring vitamin C’s role in treating colds. This book is often credited as the catalyst for the vitamin C sales boom, a phenomenon that shows no signs of waning even today.
In this book, Pauling said we should consume high doses of vitamin C, around 1,000–2,000 milligrams a day for good health, and even more to prevent a cold.
His recommendations were said to be initially from one placebo-controlled trial in children on a ski camp in the Swiss Alps. He then analysed a further four studies conducted after his claims.
But his interpretation of these studies has been widely criticised. There were incorrect mathematical analyses, reliance on four poor-quality trials and the overemphasis of the study in children.
So, do mega-doses of vitamin C work?
The short answer is not really. Multiple studies conducted since the ones Pauling analysed show that if there is an effect on vitamin C and colds, it’s minimal. Even then, any marginal benefits are only under certain circumstances, such as if you’re an athlete or in the army.
One study, published in 2023, was a meta-analysis that combined the results of ten placebo-controlled trials. These looked at the effect of vitamin C on the severity and duration of colds. In total, these trials involved 2,736 healthy people (adults, children and athletes) who regularly took at least 1,000mg of vitamin C a day, not just when they had a cold.
Overall, the researchers found people who took vitamin C had a 15 per cent reduction in severe cold symptoms compared to those who didn’t take it. This was expressed as the number of days “confined indoors”, which the authors acknowledged as a limitation. Vitamin C did not affect how long mild symptoms lasted.
A meta-analysis in 2013 found taking lower doses (at around 200mg a day) did not decrease the number of colds in the general population. However, there were fewer colds for athletes and army personnel.
Similar to the other study, regular vitamin C supplements showed a reduction in severity of symptoms in children and adults by 8–14 per cent. However, taking vitamin C at the start of the cold had no benefit.
So, from these two meta-analyses, Pauling’s original advice is over-stated. There is no evidence vitamin C will reduce your risk of catching a cold.
There is some evidence it will reduce how long severe symptoms last, but on average only by about 10 per cent. So if severe symptoms from a cold last for five days, it will reduce severe symptoms by about 12 hours. If the severe symptoms last for 24 hours, they will reduce by about two-and-a-half hours.
Taking vitamin C when symptoms start will have no effect. You need to be taking it regularly, even before you get sick.
So how much vitamin C is too much?
Pauling’s recommendation for good health, at around 1,000–2,000mg a day, is around the upper limit of what’s now considered safe to consume.
Australia has not set an upper limit for vitamin C, due to inconclusive evidence. But guidelines refer to other expert recommendations for adults to not consume more than 1,000mg a day. In the United States, the upper limit for adults is 2,000mg a day.
Pauling’s recommendation is also much higher than the recommended daily intake in Australia and other countries. For adults over 19 in Australia, this is 45mg.
This is what you would find in half an orange, three to four florets of cooked broccoli or one-third of a glass of orange juice.
So what should I do?
Taking high doses of vitamin C (over 1,000mg a day) continually can increase your risk of adverse events such as:
- Gastrointestinal effects, such as diarrhoea, nausea, stomach cramps and bloating
- More oxalate excretion, which may lead to kidney stones
- An increase in iron absorption, which may lead to tissue damage in people with undiagnosed haemochromatosis (an inherited disorder where you absorb too much iron from your food)
- Interactions with radiation therapy, chemotherapy and the cholesterol-lowering drugs statins.
If you feel you would benefit from vitamin C supplements, discuss this with your GP. You should limit the dose to below 1,000mg a day and be mindful of the side effects.
Remember less than 4 per cent of Australians are deficient in vitamin C.
Evangeline Mantzioris is the program director of human nutrition at Adelaide University and an accredited practising dietitian. She has received funding from the National Health and Medical Research Council. She has been appointed to the National Health and Medical Research Council Dietary Guideline Expert Committee. The views and opinions expressed in this article are those of the authors alone and do not represent the views of the NHMRC or the Expert Committee.
