From the first hint of cold winter mornings, supermarkets and pharmacies begin an intense marketing campaign to encourage us to stock up on vitamin C to get through the cold and flu season.
But where did that idea come from?
As we will see, it is a story that includes a Nobel Prize winner, a book and some statements that do not quite add up.
Nobel Prize winner writes a book
Linus Pauling was an American chemist who won two Nobel Prizes. one was in 1954 for chemistryfor his research on chemical bonds. The other was in 1962 for peacefor his activism against nuclear weapons testing.
He was not a dietitian or an infectious disease doctor. But that didn’t stop him publishing a book on vitamin C and colds in 1970. This book is widely credited with skyrocketing vitamin C sales at the time, a trend that continues today.
In this book, Pauling said that we should consume high doses of vitamin C, about 1,000 to 2,000 milligrams a day for good health, and even more to prevent a cold.
His recommendations were it is said to be initially from a placebo-controlled trial in children at a ski camp in the Swiss Alps. He then analyzed four other studies conducted after his claims.
But his interpretation of these studies has been widely criticized. There were incorrect mathematical analyses, reliance on four poor-quality trials, and overemphasis on the study in children.
So, do megadoses of vitamin C work?
The short answer is really no. Multiple studies conducted since those analyzed by Pauling show that if there is an effect on vitamin C and colds, it is minimal. Even then, marginal benefits occur only in certain circumstances, such as if you are an athlete or in the military.
a study, published in 2023was 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 1,000 mg of vitamin C per day, not just when they had a cold.
Overall, the researchers found that people who took vitamin C had a 15 percent reduction in severe cold symptoms compared to those who did not take it. This was expressed as the number of days “confined indoors,” which the authors recognized as a limitation. Vitamin C did not affect the duration of mild symptoms.
TO meta-analysis in 2013 It was found that taking lower doses (about 200 mg a day) did not decrease the number of colds in the general population. However, there were fewer colds among athletes and army personnel.
As in the other study, regular vitamin C supplements showed a reduction in symptom severity in children and adults by between 8% and 14%. However, taking vitamin C at the onset of a cold had no benefit.
So from these two meta-analyses, Pauling’s original advice is overstated. There is no evidence that vitamin C reduces the risk of catching a cold.
There is some evidence that it will reduce the duration of severe symptoms, but on average only by about 10%. So if severe cold symptoms last five days, severe symptoms will subside in about 12 hours. If severe symptoms last 24 hours, this will be reduced by approximately two and a half hours.
Taking vitamin C when symptoms begin will have no effect. You should take it regularly, even before you get sick.
So how much vitamin C is too much?
Pauling’s recommendation for good health, between 1,000 and 2,000 mg per day, is around the upper limit of what is now considered safe to consume.
Australia has not set a upper limit for vitamin C, due to inconclusive evidence. But the guidelines refer to other expert recommendations that adults consume no more than 1,000 mg a day. In it USAthe upper limit for adults is 2000 mg per day.
Pauling’s recommendation is also much higher than the recommended daily intake in Australia and other countries. For adults aged 19 and over in Australia, this is 45mg.
This is what you would find in half an orange, three to four florets of cooked broccoli or a third of a glass of orange juice.
So what should I do?
Taking high doses of vitamin C (more than 1000 mg per day) on an ongoing basis may increase the risk of adverse events as:
- gastrointestinal effects, such as diarrhea, nausea, stomach cramps, and bloating
- increased oxalate excretionwhich can cause kidney stones
- an increase in iron absorption, which can lead to tissue damage in people with undiagnosed diseases hemochromatosis (an inherited disorder in which too much iron is absorbed from food)
- interactions with radiotherapy, chemotherapy and statins, cholesterol-lowering drugs.
If you think you would benefit from vitamin C supplements, talk to your GP. You should limit the dose to less than 1000 mg per day and be aware of side effects.
Remember less than 4% of Australians They are deficient in vitamin C.