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Vitamin C and the common cold: the ski camp that convinced a Nobel laureate
Every year, somewhere between the first cold snap and the first blocked nose, a headline arrives to tell us that vitamin C does not stop us catching colds. It arrived again this week, in a widely syndicated piece from a nutrition academic taking apart the belief one more time. The finding is not new. It has been the settled reading of the trial literature for over a decade.
What is strange is that it keeps needing to be said.
Beliefs that survive their own evidence usually have a good story holding them up, and this one has a very good story: a chemist who had already won two Nobel Prizes, a small trial in the Swiss Alps, and a book that sold the idea to a century. The interesting part is not that the story was wrong. It is that the trial at the centre of it was right — and is still right, in the narrow group of people it actually studied.
The trial that convinced Linus Pauling
Pauling won the Nobel Prize in Chemistry in 1954 and the Peace Prize in 1962, and in 1970 he published a book recommending a gram or two of vitamin C a day. He was not inventing a hunch. Among the evidence he leaned on was a randomised, double-blind, placebo-controlled trial run by Ritzel in 1961 on schoolchildren at a skiing camp in the Swiss Alps: on one gram a day, the vitamin C group had roughly 45% fewer colds and about 61% fewer days of cold symptoms.
Those are large numbers. They are also, as far as anyone has been able to tell since, real. Ritzel's trial has held up under repeated re-examination, and later reviewers have concluded it reflects a genuine biological effect rather than a statistical accident.
So the belief did not come from nowhere. It came from a good trial, read by a brilliant man, who then did the one thing that quietly breaks most health advice: he generalised it.
What happens when you run the trial on everyone else
Over the following fifty years, the question was put to the test on a scale few nutrition questions ever get. The pooled result is unambiguous, and it is worth saying precisely because precision is the whole point here.
Across 29 placebo-controlled trials and 11,306 participants in the general population, regular vitamin C supplementation produced a pooled risk ratio for catching a cold of 0.97, with a confidence interval of 0.94 to 1.00. That is a 3% difference whose interval touches "no difference at all". In practical terms: if you are an ordinary adult eating an ordinary diet, taking vitamin C every day through the winter is not going to change how often you get sick.
But the same review contains a second number, and it is the one nobody quotes. In five trials of 598 people under heavy short-term physical stress — marathon runners, skiers, soldiers on subarctic exercises — the pooled risk ratio was 0.48, with an interval of 0.35 to 0.64. Their colds were roughly halved.
Read those two lines next to each other and the fifty-year argument dissolves. The effect never moved. The audience did. Pauling read a result from children skiing in the Alps and extended it to office workers in temperate cities, and the trials have been patiently explaining the difference ever since.
Figure 1 — pooled risk ratios
The same supplement, two different populations
The trial that ended the argument, and the argument inside it
If Ritzel's ski camp is the trial that started the belief, a 1975 trial at the US National Institutes of Health is the one usually credited with ending it — and it is a small masterpiece of how evidence actually behaves.
Karlowski and colleagues ran NIH employees through nine months of capsules, with separate daily and during-illness capsules at three grams each. In the arm taking both — six grams a day while ill — colds ran about 17% shorter, a little over a day. Then they argued that their own positive result should be discarded, because the blinding had broken: the placebo capsules were lactose, which tastes sweet, and ascorbic acid does not. Participants could tell. A subgroup who had not tasted their capsules showed a much smaller effect, and the authors concluded the benefit could be explained by expectation rather than chemistry.
That conclusion travelled for decades. In 1996, Hemilä went back to the data and pointed out that the reasoning ran the wrong way round: participants who had spent the winter getting colds tended to conclude they were on placebo, and participants who stayed well tended to conclude they were on vitamin C. Guessing correctly was not necessarily a cause of the result. It could just as easily have been a consequence of it.
Nobody in this story is a villain. Two sets of careful scientists looked at one dataset and each found the reading that matched what they already suspected. That is worth remembering the next time a single study is described to you as settling something.
Four different questions, four different answers
Most of the confusion around vitamin C is not really disagreement. It is four separate questions being answered at once and the answers being averaged into a shrug.
Figure 2 — what the trials asked
"Does vitamin C work?" is four questions
Not in the general population. RR 0.97 across 11,306 people. Halved in trials of marathon runners, skiers and soldiers.
Taken regularly, before the cold: 8% shorter in adults (3–12%), 14% in children (7–21%).
15% reduction in severity (9–21%) across 10 trials at 1 g/day or more — concentrated in the severe symptoms, not the mild ones.
No consistent effect on duration or severity in the trials that began dosing after symptoms had already started.
Why the severity finding is the one that changed
Earlier reviews pooled "duration of cold" as a single outcome, which mixes a day of sniffles with a day spent unable to work. The 2023 analysis separated them across 15 comparisons from 10 trials and found the benefit sat almost entirely in the severe end: a significant effect on the duration of severe symptoms, no significant effect on mild ones, and a statistically significant difference between the two (P = 0.002). A small average can hide an uneven distribution.
What vitamin C is actually for
Underneath the argument about colds, vitamin C's real job description is unglamorous and completely uncontested. In the EU, the authorised claim is that vitamin C contributes to the normal function of the immune system. That is a statement about a system working normally. It is not a promise that a system will out-perform a virus, and the gap between those two sentences is where fifty years of marketing has lived.
The adult reference intake sits somewhere between 45 and 90 mg a day depending on your sex and which national body is writing the guidance, with a tolerable upper limit for supplements around a gram or two. Actual deficiency is rare in countries with year-round produce — under 4% of the population in the Australian figures cited this week. Most people asking whether they should take more vitamin C are already replete, which is exactly the condition under which supplementing something changes the least.
This is the same trap we wrote about when we looked at what the liposomal vitamin C trials actually show. Those trials are real, and the absorption advantage is measurable. But absorption is an input, not an outcome. Getting more of a nutrient into a bloodstream that already has enough is a solved problem in search of a benefit.
So who was the ski camp, and are you in it?
The honest version of the advice is not "vitamin C does nothing". It is: the effect scales with how hard your body is being worked and how thin your intake is. The people in whom vitamin C halved colds were not healthier than average. They were being put through something — subarctic military exercises, competitive endurance events, a week of skiing in the cold as a child.
If you are training seriously through winter, working outdoors in the cold, or coming off a period where fruit and vegetables have genuinely dropped out of your week, you are closer to the group where the trials found something than the group where they did not. If you are otherwise well-fed and moderately active, the reasonable expectation is a slightly less miserable cold rather than one that never arrives.
Either way, the useful thing to notice this week is not a dose. It is a habit of reading. Ask, of any supplement result, four questions in order: who was studied, what exactly was measured, was the effect on the average or on the bad end, and does the trial population resemble me? Pauling got the first three right. It was the fourth that undid him — and it is the fourth that most wellness advice still skips.
That habit generalises well beyond a vitamin. It is the same discipline behind how we score the evidence behind every ingredient we sell, including when the score comes back inconvenient.
The bottom line
Vitamin C will very probably not stop you catching a cold this winter, and the trials have been consistent about that for a long time. Taken regularly — not started at the first sneeze — it makes colds a little shorter and, on the better analysis, meaningfully less severe at the bad end, which is not nothing when a bad cold costs you a working week.
The larger lesson is the one hiding in the ski camp. A real finding in a specific population became a universal rule because it was told well, by someone credible, in a book. Fifty years and 11,000 participants later, the finding is exactly where it always was. Nobody moved it. We just kept assuming it applied to us.
