In short
- There’s restricted proof that vitamin C is helpful for a chilly.
- A Nobel Prize winner’s ebook is broadly credited with sparking the idea.
From the primary trace of chilly winter mornings, supermarkets and pharmacies start heavy advertising and marketing to coax us to top off on vitamin C to get by way of the chilly and flu season.
However the place did that concept come from?
As we’ll see, it’s a narrative together with a Nobel Prize winner, a ebook and a few claims that don’t fairly stack up.
Nobel Prize winner writes a ebook
Linus Pauling was a chemist from the US who received two Nobel Prizes. One was in 1954 for chemistry, for his analysis into chemical bonds. The opposite was in 1962 for peace, for his activism towards nuclear weapons testing.
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He was not a dietitian or an infectious illness doctor. However that didn’t cease him publishing a ebook on vitamin C and colds in 1970. This ebook is broadly credited with the skyrocketing gross sales of vitamin C on the time, a pattern that continues at this time.
On this ebook, Pauling mentioned we should always eat excessive doses of vitamin C, round 1,000–2,000 milligrams a day for good well being, and much more to forestall a chilly.
His suggestions have been mentioned to be initially from one placebo-controlled trial in kids on a ski camp within the Swiss Alps. He then analysed an additional 4 research performed after his claims.
However his interpretation of those research has been broadly criticised. There have been incorrect mathematical analyses, reliance on 4 poor-quality trials and the overemphasis of the research in kids.
So, do mega-doses of vitamin C work?
The quick reply shouldn’t be actually. A number of research performed because the ones Pauling analysed present that if there’s an impact on vitamin C and colds, it’s minimal. Even then, any marginal advantages are solely below sure circumstances, akin to when you’re an athlete or within the military.
One research, printed in 2023, was a meta-analysis that mixed the outcomes of ten placebo-controlled trials. These regarded on the impact of vitamin C on the severity and period of colds. In whole, these trials concerned 2,736 wholesome folks (adults, kids and athletes) who usually took at the very least 1,000mg of vitamin C a day, not simply after they had a chilly.
General, the researchers discovered individuals who took vitamin C had a 15 per cent discount in extreme chilly signs in comparison with those that didn’t take it. This was expressed because the variety of days “confined indoors”, which the authors acknowledged as a limitation. Vitamin C didn’t have an effect on how lengthy gentle signs lasted.
A meta-analysis in 2013 discovered taking decrease doses (at round 200mg a day) didn’t lower the variety of colds within the normal inhabitants. Nonetheless, there have been fewer colds for athletes and military personnel.
Just like the opposite research, common vitamin C dietary supplements confirmed a discount in severity of signs in kids and adults by 8–14 per cent. Nonetheless, taking vitamin C in the beginning of the chilly had no profit.
So, from these two meta-analyses, Pauling’s unique recommendation is over-stated. There isn’t any proof vitamin C will cut back your threat of catching a chilly.
There may be some proof it’s going to cut back how lengthy extreme signs final, however on common solely by about 10 per cent. So if extreme signs from a chilly final for 5 days, it’s going to cut back extreme signs by about 12 hours. If the extreme signs final for twenty-four hours, they may cut back by about two-and-a-half hours.
Taking vitamin C when signs begin may have no impact. It’s essential be taking it usually, even earlier than you get sick.
So how a lot vitamin C is an excessive amount of?
Pauling’s advice for good well being, at round 1,000–2,000mg a day, is across the higher restrict of what’s now thought of secure to eat.
Australia has not set an higher restrict for vitamin C, on account of inconclusive proof. However tips consult with different knowledgeable suggestions for adults to not eat greater than 1,000mg a day. In the US, the higher restrict for adults is 2,000mg a day.
Pauling’s advice can be a lot increased than the really helpful day by day consumption in Australia and different nations. For adults over 19 in Australia, that is 45mg.
That is what you’ll discover in half an orange, three to 4 florets of cooked broccoli or one-third of a glass of orange juice.
So what ought to I do?
Taking excessive doses of vitamin C (over 1,000mg a day) regularly can enhance your threat of opposed occasions akin to:
- Gastrointestinal results, akin to diarrhoea, nausea, abdomen cramps and bloating
- Extra oxalate excretion, which can result in kidney stones
- A rise in iron absorption, which can result in tissue harm in folks with undiagnosed haemochromatosis (an inherited dysfunction the place you soak up an excessive amount of iron out of your meals)
- Interactions with radiation remedy, chemotherapy and the cholesterol-lowering medicine statins.
If you happen to really feel you’ll profit from vitamin C dietary supplements, talk about this together with your GP. You must restrict the dose to beneath 1,000mg a day and be aware of the unwanted effects.
Bear in mind lower than 4 per cent of Australians are poor in vitamin C.
Evangeline Mantzioris is this system director of human vitamin at Adelaide College and an accredited practising dietitian. She has acquired funding from the Nationwide Well being and Medical Analysis Council. She has been appointed to the Nationwide Well being and Medical Analysis Council Dietary Guideline Professional Committee. The views and opinions expressed on this article are these of the authors alone and don’t characterize the views of the NHMRC or the Professional Committee.
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