Vitamin C: can it cure colds and cancer?

Summary

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Podcast Summary: What's That Rash?

Episode: "Vitamin C: can it cure colds and cancer?"

Host: Norman Swan
Co-host/Expert: Dr. Danielle
Date: March 3, 2026
Podcast by: ABC News

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Episode Overview

This episode tackles one of the most asked health questions: Does vitamin C supplementation actually prevent or cure colds and cancer? Listeners Angeline, Claude, and Beatrice have written in with queries ranging from everyday vitamin C intake to high-dose IV therapy. Dr. Danielle and Norman Swan explore the science — and myths — behind vitamin C, its historic association with scurvy, Linus Pauling’s controversial advocacy, and what modern research really tells us about vitamin C’s powers and pitfalls.

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Key Discussion Points & Insights

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1. What Is a Vitamin?

[03:03 – 03:55]

• Dr. Danielle defines vitamins as micronutrients "in other words, small dose that your body needs to survive to important metabolic processes that we can't make ourselves. The one exception to that is vitamin D, which you can make yourself when exposed to sunlight" (03:12).
• Humans, unlike most animals, cannot synthesize vitamin C themselves and must obtain it from the diet, particularly fruits and vegetables.

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2. The History of Vitamin C and Scurvy

[04:14 – 07:57]

• Scurvy is a disease caused by vitamin C deficiency, resulting historically in "a luxuriancy of funguous flesh, putrid gums, and the most dreadful terrors and sudden death" (Norman Swan, 04:39).
• The British Navy’s struggle with scurvy is recounted, with lemon juice being an early remedy, though the connection was not firmly established at first.
• Fun fact: Sailors who ate ship’s rats got vitamin C, since rats produce it themselves.

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3. The Naming and Discovery of Vitamin C

[07:26 – 07:57]

• Albert St. Giorgi discovered and chemically identified vitamin C, originally calling it "hexuronic acid" before settling on "ascorbic acid," meaning anti-scurvy (Norman Swan, 07:49).

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4. Linus Pauling and the Vitamin C Hype

[08:02 – 10:44]

• Nobel laureate Linus Pauling popularized the idea that high-dose vitamin C could extend life, cure colds, and even prevent cancer; this became known as "orthomolecular medicine."
• Dr. Danielle: "He was criticised for his views on vitamin C and by the mainstream medical community... there was really very little or no research to back this up." (10:06).
• Subsequent randomized trials show that vitamin C "at best, might shorten the duration of symptoms" for the common cold, but not prevent or cure it.

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5. Immune Boosting, Cancer, and IV Vitamin C

[10:44 – 14:20]

• Antioxidant Role: In small, food-derived doses, vitamin C acts as an antioxidant alongside other micronutrients.
• High-Dose IV Vitamin C: At high intravenous doses, vitamin C paradoxically becomes a "pro-oxidant," causing damage rather than protection, and can even kill healthy cells.
  • "There is an anti-cancer effect, but it's not because it's good for your body, it's because it's bad for your body" (Dr. Danielle, 12:45).
  • Some evidence suggests it might enhance chemotherapy, especially in pancreatic cancer, but it’s not “ready for showtime.”
• Cancer Clinical Trials: The effectiveness of IV vitamin C is still uncertain, and oral high-dose supplementation has not shown any significant anti-cancer effects (Norman Swan & Dr. Danielle, 13:59).
• Kidney Stone Risk: Excessive intake can cause kidney stones, placing a burden on the kidneys (Dr. Danielle, 16:23).

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6. Should You Supplement or Eat Your Vitamin C?

[15:03 – 16:03]

• Dr. Danielle's bottom line: "You would avoid high dose supplementation? You would avoid supplementation altogether, to be honest, and really just take it in the diet because it's meant to be taken in relatively small doses with other bioactive compounds... so you really stick with what we know is that food works” (15:03).
• Only 8 mg/day is needed to prevent scurvy; a single orange or even a potato provides more than enough.
• “You should be eating five and two [serves of vegetables and fruit] every day anyway, for all sorts of different reasons. I guess what I'm trying to say here is don't stress too much about it.” (Norman Swan, 15:45).

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Notable Quotes & Memorable Moments

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• Norman Swan (on childhood vitamin C tablets): "I think there's something Pavlovian about it. Like as a kid it felt like maybe getting a bit of a treat and so even as an adult when I see them I'm like, ooh, yummy treat." ([01:17])
• Dr. Danielle (debunking mega doses): "In high doses, particularly when it's given intravenously, it turns into a pro oxidant... when you take very high doses intravenously, you're taking vitamin C as a drug which actually can damage cells." ([12:10])
• Dr. Danielle: "You would avoid supplementation altogether... just take it in the diet because it's meant to be taken in relatively small doses with other bioactive compounds." ([15:03])
• Norman Swan (on scurvy and potatoes): "One potato has 27 milligrams of vitamin C. Well, speaking of potatoes, scurvy broke out in Ireland with the potato blight in the 19th century." ([15:40])
• Dr. Danielle (about Linus Pauling): “He lived a long time. I think he went to his 90s, but he was extolling the virtues of vitamin C for cancer and unfortunately died the following year of cancer. But, you know, it's not schadenfreude, just unfortunate." ([16:03])
• Dr. Danielle (on supplements): "So those yummy little chews that I was saying before, probably not worth it... you might get a pain in the side" ([16:37–16:41])

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Segment Timestamps

• Vitamin C in Diet vs. Supplements: 01:03 – 02:31
• What Is a Vitamin?: 03:03 – 03:55
• Scurvy and Vitamin C Deficiency: 04:14 – 06:50
• Discovery and Naming: 07:26 – 07:57
• Linus Pauling’s Influence/Missteps: 08:02 – 10:44
• Vitamin C in Immune Health/Cancer: 10:44 – 14:20
• Should You Supplement?: 15:03 – 16:03
• Kidney Stone Risk: 16:23 – 16:37

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Summary Takeaways

• There is no robust evidence that vitamin C supplementation prevents colds or cancer.
• Most people can easily get sufficient vitamin C from a regular diet; deficiency is rare.
• High doses, especially IV, are only possibly relevant as adjuncts in certain cancer treatments, but this approach is experimental and risky due to potential cell and kidney damage.
• Stick to the “five and two” rule of fruit and veg — and skip the megadoses and chewy vitamin C sweets.

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For questions or corrections, email the team at [e-mail].

Transcript

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[Norman Swan]

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[Norman Swan]

Yep, yep, we're trying to track them down.

[Dominique Bayans]

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[Norman Swan]

Norman, I know that you're not a supplement guy, but if I could choose one supplement to have, it would definitely be the chewy vitamin C. Oh, really? They're yummy. They taste like a lolly.

[Dr. Danielle]

Has it got sugar in it? Is it rotting your teeth too?

[Norman Swan]

No, I think they're called sugarless C or something like that. I think there's something Pavlovian about it. Like as a kid it felt like maybe getting a bit of a treat and so even as an adult when I see them I'm like, ooh, yummy treat.

[Dr. Danielle]

And have you been relieved of a cold as a result?

[Norman Swan]

No, you've cured me of wanting any supplements which I spoil is kind of preempting the answer to today's question here

[Dr. Danielle]

on I might be wrong. I might be wrong. So let's just not give it away here.

[Norman Swan]

All right, all right, all right. Well, let's get into it. This is of course, what's that Rash.

[Dr. Danielle]

The podcast which answers the health questions that everybody's asking

[Norman Swan]

people today, Norman, are asking about vitamin C supplementation. Angeline says, I tend to catch colds and flu pretty easily, so I try to get the flu shot each year and generally keep a healthy lifestyle. In recent years I've also started taking vitamin C, a thousand milligram daily dose. I'm not sure if it's actually helped me. Is there any evidence vitamin C supplements work and if so, how much should we take daily? My brother in law takes 2,000 milligrams every day and he never seems to get sick. He claims that it's the vitamin C that does it. Claude has also emailed saying, although I prefer to get my vitamins from Food rather than supplements. I tend to have one or two chewable C's a day.

[Dr. Danielle]

Oh, he's onto the same thing as you.

[Norman Swan]

Yeah, they taste good. I remember reading a study that said the more C in your blood, the less cannabis cancer cells. Also, it's associated with boosting the immune system, but I've heard you say it can be counterproductive. And someone said it's hard on the kidneys. And then Beatrice is blowing everyone else out of the water asking about mega doses of vitamin C, like 60,000 milligrams administered via an IV drip. Is it safe? So, yeah. We've got questions about vitamin C today, Norman.

[Dr. Danielle]

We have, and it's got a rich history.

[Norman Swan]

Oh, my gosh.

[Dr. Danielle]

Well, we should explain what a vitamin is to start with. You say vitamins, I say vitamins.

[Norman Swan]

All I want to talk about is scurvy. But fine, let's talk about it. What is the definition of a vitamin?

[Dr. Danielle]

A vitamin is micronutrient. And we'll come back to this idea of a micronutrient. In other words, small dose that your body needs to survive to important metabolic processes that we can't make ourselves. The one exception to that is vitamin D, which you can make yourself when exposed to sunlight. But most of the vitamins are ones where you actually need to take them via your mouth.

[Norman Swan]

And for an animal, say a human that needs something but can't manufacture it in their body, we're actually pretty well adapted to getting it out of the food that we eat. So for most humans, vitamin C, you get it most notoriously through fruit and vegetables. And I think most people associate vitamin C specifically with citrus fruit because they are very high in it.

[Dr. Danielle]

Indeed. And there are animals that can make their own vitamin C, but not humans.

[Norman Swan]

Most animals can make their own vitamin C. That's what's actually really wild to humans. And most primates, but not all primates and bats also need to supplement vitamin C from their diet. But most other animals can just, like, figure it out by themselves.

[Dr. Danielle]

So let's get to scurvy. How can we stay away from it?

[Norman Swan]

I thought you'd never ask. I think if you are informed enough about health to be listening to what's that rash. You probably know that scurvy is a vitamin C deficiency. Just a little recap on how scurvy presents in the body. It's hectic. Vitamin C is important in the manufacturing of collagen, which is pretty important for, like, our bodies sticking together.

[Dr. Danielle]

It's part of our connective tissue.

[Norman Swan]

And so then the Symptoms of scurvy. Well, let me read to you part of the ship's log from Commander George Anson. This is from a British exhibition in the 1740s. They lost. They lost 1,300 of an original 2,000 men to illness, at least some of which to scurvy. And he described almost the whole crew was afflicted by symptoms, including a luxuriancy of funguous flesh, putrid gums, and the most dreadful terrors and sudden death. Why do you die from it?

[Dr. Danielle]

Well, your body essentially falls apart and you bleed and you get internal haemorrhage and external haemorrhage, basically body failure.

[Norman Swan]

The thing with scurvy that's interesting to me is that the cure for it is really simple. Vitamin C almost straight away starts to reverse the effects of scurvy. And it's something that humans have kind of known about and then forgotten and rediscovered and forgotten and rediscovered over a few thousand years. There's even in ancient Egyptian texts, this idea that eating vegetables can help prevent it.

[Dr. Danielle]

But we've made a false hero here, though, our discovery, haven't we?

[Norman Swan]

In the British Navy, there's a few heroes. Are you talking about Lind?

[Dr. Danielle]

James Lynde, who found that lemon juice improved scurvy, but he actually never really tied that down.

[Norman Swan]

He also blamed a lot of things on damp air, which, I mean, people loved to blame things on air back in those days. And to be fair, I can only

[Dr. Danielle]

imagine you and I did for Covid a lot.

[Norman Swan]

Well, that's true.

[Dr. Danielle]

Maybe you should have been taking vitamin C. No, no, I'm not going to be on that track again.

[Norman Swan]

No, let's not go there, please. No. I mean, obviously some diseases, aerosol and airborne diseases, vitamin deficiency is not one of them. But I can only imagine what the inside of a ship's hull smelt like after 10 or 12 weeks at sea. So maybe it's a defensible thing. Also, on ships hulls, sailors who ate the ship's rats were inadvertently protecting themselves against scurvy, because rats are one of the creatures that can synthesise their own vitamin C. And if you were a hungry enough sailor to eat a rat, you probably were getting vitamin C from that rat.

[Dr. Danielle]

And Lyndon never smelled a la in terms of his research.

[Norman Swan]

Exactly. So Lind is the person that we often kind of associate with vitamin C and scurvy prevention. But there was a couple of generations of scientists that sort of built on that research to take us to knowing about vitamin C specifically and also synthesizing it, a couple of really Important people in this journey. Albert St. Giorgi, who was awarded the 1937 Nobel Prize in Physiology or Medicine, he was one of the people that got the chemical structure nailed down. He didn't want to call it vitamin. Do you know what he wanted to call it?

[Dr. Danielle]

I think he called it hexuronic acid

[Norman Swan]

or something, didn't he, before he called it that? So you know how if something's a sugar that it's sometimes got the suffix O S, E, like ose he wanted to call it, God knows, because he didn't really know what it was for, but he knew it was a sugar of some sort.

[Dr. Danielle]

Hilarious.

[Norman Swan]

Anyway, basically they figured it out. It was the same thing as ascorbic acid. Do you know why it's called ascorbic acid?

[Dr. Danielle]

No, I don't.

[Norman Swan]

A as in preventing or against scorby. Scurvy. It's anti scurvy acid. That's really where the name comes from.

[Dr. Danielle]

But then we have another Nobel laureate who gets involved in the vitamin C story.

[Norman Swan]

Are you talking about Linus Pauling?

[Dr. Danielle]

I am.

[Norman Swan]

This is a really weird sidebar.

[Dr. Danielle]

So lies weren't a sidebar. He was front and center anyway.

[Norman Swan]

So I suppose the thing to say about Linus Pauling is he's a. He's a Nobel Laureate. So his field of science was chemistry and structural chemistry.

[Dr. Danielle]

Really very, very basic chemistry in which modern chemistry is built. So it was a brilliant Nobel Prize. But like a few Nobel laureates, he expanded beyond his area of expertise. But pretty much like a medical journalist,

[Norman Swan]

I'll let you say it, not me. He actually won two Nobel Prizes. So he won one for chemistry. Good for him. And then he also won a second Nobel in 1963, the Peace Prize, for his work towards nuclear disarma. So he was a politically charged figure. He was sort of tarred with the communist brush. But in addition to that, he suffered from some health issues. And in his kind of quest to keep himself healthy, he sort of fell down. A bit of a vitamin C rabbit hole that we're kind of really only just climbing out of today.

[Dr. Danielle]

He became a major promoter of vitamin C for extended lifespan, extended healthy lifespan, and indeed to prevent the common cold. He just thought vitamin C was an amazing compound that had huge health benefits, not just in preventing infection, but also preventing cancer.

[Norman Swan]

So Pauling's thing was what he would eventually call orthomolecular medicine. It's a Greek prefix, ortho, meaning sort of straight or correct or right. And his idea was that if you had the right molecules in your body, you could cure a whole suite of health problems. And I suppose it's fitting that vitamin C is in this debate because you have a deficiency disease which is scurvy, and you have a vitamin which cures it. And he wanted to kind of extend that, to be like, what if you had even more and you could cure other things as well. And his devotion to the idea that it could be something of a cure all has had some real long term ripples in terms of our understanding of what this vitamin can do.

[Dr. Danielle]

And it spawned a lot of research. So he was criticised for his views on vitamin C and by the mainstream medical community. Now, the mainstream medical community has been wrong about a lot of things, but there was really very little or no research to back this up. He became an author in a few papers which were poorly conducted, and he really was unable to prove scientifically his assertions about vitamin C. And around that time, and subsequently, people have done randomized trials of vitamin C supplementation in the prevention of the common cold and found that at best, it might shorten the duration of symptoms. But that's about it.

[Norman Swan]

So I think some of the big claims around vitamin C are common cold, like you said, immune system, broadly, maybe it's protecting you against colds, maybe it's protecting you against other things as well. And then cancer prevention, especially. That third question that we got, which was about big IV doses. Let's talk through what we actually know about these three things.

[Dr. Danielle]

Let's go back to that comment I made right at the beginning, that vitamins are really micronutrients. They work in the body in small, relatively small doses associated with other compounds in food that almost certainly help those vitamins and other micronutrients to work. So vitamin C in doses that you would get in foods, is actually an antioxidant. So the oxidative process is part of that aging process. It's the toxicity of oxygen essentially rusting your tissues from the inside out. So the idea here is that you have these antioxidants, one of which is vitamin C, which help mop up this process, but not by themselves in association with other bioactive compounds. So here's the weird thing, which Pauling never actually knew about and has only been known about recently for reasons which are not fully understood. In high doses, particularly when it's given intravenously, it turns into a pro oxidant. In other words, it speeds up the damage to tissues and the aging process. So when you take very high doses intravenously, you're taking vitamin C as a Drug which actually can damage cells. So there is in fact, it turns out almost certainly an anti cancer effect of high dose intravenous vitamin C which by itself does not seem to have any significant effect on cancer, but when given with other chemotherapeutic agents seems to enhance their effects. Now the evidence is not brilliant on that. There are clinical trials still going on. Little bit of evidence of prolonged surv in pancreatic cancer when hydro's vitamin C is used in association with chemotherapy. So it's not yet ready for showtime. But there is an anti cancer effect, but it's not because it's good for your body, it's because it's bad for your body.

[Norman Swan]

It's killing cancer cells. It can kill your healthy cells as well by the sounds of it.

[Dr. Danielle]

Absolutely. Yep.

[Norman Swan]

Because I was gonna say, like, why on earth do we even have these high dose vitamin C supplements being offered? But it turns out there could be an application for them, but it's a pretty narrow part of the population.

[Dr. Danielle]

Yeah. And it doesn't look as though it works when you take it orally.

[Norman Swan]

I think the thing with the end of Pauling's story is it ended up being this big beef where he was very pro high dose vitamin C infusions because it was controversial, because he was a controversial guy. The Mayo Clinic did some trials basically showing that his theory didn't work. But they used a different method of delivery. They used an oral delivery instead of an intravenous delivery. Anyway, without getting too much into the weeds, people who've commented on this have kind of observed that this whole back and forth with Pauling put the research into vitamin C back decades because it was kind of tainted by this episode.

[Dr. Danielle]

Yeah, but those orthomolecular physicians who are still around actually give high dose intravenous vitamin C. And from the evidence that we've got, it's not something you particularly want to have. Interestingly, the Australian Institute of Sport uses vitamin C after intense exercise to help repair muscles.

[Norman Swan]

This is what I wanted to ask about. What's it doing in muscles? And has this got anything to do with this idea that overall it might be good for your immune system?

[Dr. Danielle]

Well, what they're doing is trying to. The theory is after intense exercise you get increased oxidation, what's called reactive oxygen species, and you give the vitamin C to reduce these reactive oxygen species, which you'd have to say that if it was really high dose, you'd have question whether or not they're achieving their end there. But they do seem to have some evidence to back them up.

[Norman Swan]

Okay, so to kind of bring this home, Angelina and Claude were both asking about moderate level vitamin C supplementation. Beatrice is asking about this really high level vitamin C supplementation. What do we say?

[Dr. Danielle]

You would avoid high dose supplementation? You would avoid supplementation altogether, to be honest, and really just take it in the diet because it's meant to be taken in relatively small doses with other bioactive compounds. Bioactive compounds that have yet to be identified, some of which have, but some of which haven't. So you really stick with what we know is that food works.

[Norman Swan]

Food works. And I think just for some, like, clarity, if you don't want to get scurvy, you only need about 8 milligrams a day of vitamin C. You can get this from 100 grams of onion, like one orange. One potato has 27 milligrams of vitamin

[Dr. Danielle]

C. Well, speaking of potatoes, scurvy broke out in Ireland with the potato BLIGHT in the 19th century.

[Norman Swan]

Exactly. And I think we think of citrus fruits as being very, very high vitamin C. And they are. But you actually don't need to eat very much fruit and vegetables to get what you need in terms of vitamin C. You should be eating five and two every day anyway, for all sorts of different reasons. I guess what I'm trying to say here is don't stress too much about it.

[Dr. Danielle]

And the sad story with Pauling, I mean, he lived a long time. I think he went to his 90s, but he was extolling the virtues of vitamin C for cancer and unfortunately died the following year of cancer. But, you know, it's not schadenfreude, just unfortunate.

[Norman Swan]

Exactly. And I guess the fact that we're all human, even if we're really, really

[Dr. Danielle]

smart, and there was a question about the damage to kidneys. And in fact, too much vitamin C can produce kidney stones, so there is a burden on the kidneys from too much vitamin C potentially producing kidney stones. You don't want to get a kidney stone very painful.

[Norman Swan]

So those yummy little chews that I was saying before, probably not worth it.

[Dr. Danielle]

Probably not worth it. You might get a pain in the side.

[Norman Swan]

Angeline, Claude, Beatrice, thank you all so much for asking us your question. You can ask us your question by emailing thatrashbc.net au what's in the meal bag? Megan says, I recently listened to your podcast on peptides, and she says before a recent hike, one of our group got injured and to aid a speedy recovery, did everything they could in inverted commas, including injecting peptides There were two occasions peptides were injected and they suffered a reaction that increased their heart rate. So the group member went on the hike, no problem, but then returned. They got suspicious about the bacteriostatic water that was used to inject the peptide. So they got this bacteriostatic water, they sniffed it, they got their hands on it and sort of rubbed it on their hands again a couple of minutes. Severe rise in their heart rate and blood pressure. Some skin tingling, some dizziness, tremors lasting 30 minutes with zero localised reactions such as redness and itching or swelling. And then two days later had a similar episode at work. What on earth could be going on here? And I can't remember if we went into bacteriostatic water, what it even is.

[Dr. Danielle]

Norman, look like anything that you buy online, you've no idea what was in it. So there could have been an adrenaline like substance in the water. There could be another chemical that affects the cardiovascular system. You just. Just don't know all sorts of things. You've just got no idea what you're injecting.

[Norman Swan]

So just like massive. Proceed with caution. Sign here.

[Dr. Danielle]

You don't know what you're buying.

[Norman Swan]

Well, Megan, thank you so much for the question. Also, Norman, I'm smarting because two different people have emailed us to correct my pronunciation of the word asterisk, which I do know how to pronounce. Sometimes my brain just works faster than my mouth does.

[Dr. Danielle]

Yeah, apparently you said asterisks.

[Norman Swan]

I did. And I actually really enjoyed the asterisks and obelisk comics when I was a kid. So thank you for the trip down memory lane.

[Dr. Danielle]

Yeah, yeah. Just an asterisk in history if you

[Norman Swan]

want to correct Norman's pronunciation on anything. The email address is that rash ABC Net au.

[Dr. Danielle]

You say tomato, I say tomato. You say potato, I say potato. La la la la la. Let's call the whole thing off. But we're not calling the whole thing off. We'll see you next week. See you then.