Earlier this month, one of the most rigorous trials ever run on a vitamin was stopped early — because the people getting the vitamin were dying faster than the people getting nothing [1].
It was vitamin C. High-dose, into the vein, in patients with severe burns. The idea sounded right: burns flood the body with damage, vitamin C mops up that damage, so give plenty.
It proved the opposite. Deaths roughly doubled. The safety board halted the trial [1].
And here's why it matters even if you never touch an IV: the same trap — assuming more of a "good" antioxidant is automatically better — has backfired over and over with the pills on the shelf.
Table of Contents
The dramatic case
Start with why the burn trial sounded so right.
A severe burn sets off a storm of what scientists call oxidative stress — think of it as cellular rust, free radicals tearing at tissue. Vitamin C is an antioxidant; it neutralises that kind of damage. So the logic was simple: more rust, so add more rust-remover.
The dose tells you how far past normal they went — 50 milligrams per kilogram, every six hours, for four days. For a typical adult, that works out to roughly 14 to 16 grams of vitamin C a day, delivered straight into the bloodstream. Compare that with the 75 to 90 milligrams most adults need in an entire day [2]. This was not nutritional supplementation. It was a pharmacologic flood.
And the flood backfired. The main result — death or lasting organ failure — went the wrong way [1].
I want to be careful with the death number, because the trial stopped with relatively few deaths, so the exact size is uncertain. But every way they looked at it, it pointed the same way — roughly a doubling. That's why the oversight board pulled the plug.
And it wasn't a one-off. The exact same dose of intravenous vitamin C had been tested four years earlier in a completely different group of critically ill patients — people with sepsis — and it did the same thing: a higher rate of death or organ failure, 44.5% versus 38.5% [3].
Two trials. Same flood. Two different sets of very sick people. Same wrong direction.
So how does an antioxidant end up doing harm? And the mechanism here matters for what you decide to do with your own supplement routine. The researchers point to two things. First, your kidneys turn excess vitamin C into oxalate, and a flood of it can crystallise and damage the kidneys — exactly the wrong thing in someone already fighting for their organs. And second — the part that sounds like a paradox. Vitamin C is normally a free-radical mop. But a badly burned body is flooded with loose iron from damaged tissue, and when you add a massive dose of vitamin C to that, the chemistry can run backwards: instead of soaking up free radicals, the vitamin starts making them, producing hydrogen peroxide that harms the very cells it was meant to protect. The antioxidant becomes a pro-oxidant — it's actually the same reaction scientists have tried to use to kill cancer cells. The authors are careful to call this a likely explanation, not a proven one. Same molecule — but flooded into a body already in crisis, it does the opposite.
And it's not just in the ICU that the "more is better" approach has backfired. In the supplement space, "more is better" has backfired for decades.
The wrong way
The pattern is almost always the same: an antioxidant looks great on paper, so people take a big dose of it, and the careful trial finds the opposite.
Start with beta-carotene — a building block your body turns into vitamin A. On paper, a beautiful cancer-fighter. So researchers gave it to more than 18,000 people at high risk of lung cancer — smokers, former smokers, asbestos workers. The beta-carotene group got 28% more lung cancer. That trial was stopped early too [4].
And that wasn't the only one — a separate large trial in male smokers had found the same kind of signal, about 18% more lung cancer in the beta-carotene group [5].
Then vitamin A on its own. A huge review pulling together 67 trials and more than 230,000 people found that, in the most careful studies, antioxidant supplements as a group slightly raised the risk of dying — and vitamin A was one of the worst, raising it by 16% [6].
Now vitamin E — and this is the one that should stop people, because it wasn't sick patients and it wasn't smokers. It was one of the largest prevention trials ever run: about 35,000 healthy men, given a common megadose of vitamin E — 400 international units a day. To put that in perspective, that's many times the amount you'd get from a normal diet, sold as a single capsule. The men on vitamin E ended up with significantly more prostate cancer [7].
So here's where the official recommendation has landed. In 2022, an independent government panel — the US Preventive Services Task Force — looked at all of it and said it plainly: it recommends against the use of beta-carotene or vitamin E supplements for the prevention of cardiovascular disease or cancer [8].
Notice the careful wording there, because it's honest. For beta-carotene, they said the harms outweigh the benefits. For vitamin E, they didn't say it kills you — they said there's no net benefit. The clear harm signal for vitamin E comes from the prostate-cancer trial and that big review. The takeaway is simpler than any single number: taking a lot of one antioxidant has, again and again, done nothing useful and sometimes done real harm.
And right about now, a lot of people are going to raise a common objection — so let me take it head-on. The argument goes: those vitamin E trials all used one synthetic form, called alpha-tocopherol. The "full-spectrum" forms — tocotrienols — are supposed to be safer.
The problem is that, at the moment, we just aren't sure. Researchers gathered every randomised tocotrienol trial in humans — 30 trials, about 2,600 people — and every single one measured short-term blood markers. Not one tracked whether people lived longer, or got less cancer, or had fewer heart attacks. Most ran only weeks to months [9].
So the harm from high-dose alpha-tocopherol is real and measured. The idea that a different form must therefore be safe is just an assumption — with no long-term trial behind it. And that is exactly the "sounds good on paper" reasoning that keeps getting people into trouble. Plausible? Maybe. Proven? Not even close.
So used the wrong way — wrong dose, wrong population, wrong assumptions about form — these things backfire. But used the right way, antioxidants genuinely help. And the cleanest proof of that starts with the exact question we just raised: does the form matter?
The right way
It does. And the best example in all of medicine starts with the same villain from a minute ago — beta-carotene.
There's a common eye disease called age-related macular degeneration. It slowly destroys the centre of your vision, and for a long time the one thing that genuinely slowed it down was a specific antioxidant supplement formula — vitamins C and E, zinc, and beta-carotene. It worked. It cut the risk of the disease getting worse by about a quarter [10].
But there was a problem sitting inside that formula: the beta-carotene. The same building block that, in those big trials, raised lung cancer in people who'd smoked. You had this strange situation where the treatment that saved people's vision contained the ingredient that, in the wrong population, raised cancer risk.
So researchers started looking for an alternative. Lutein and zeaxanthin are the pigments that give corn and egg yolks their yellow colour, and the body deliberately stockpiles them in one tiny spot — the very centre of the retina, the part that does your sharpest vision. They sit there as a built-in filter, soaking up the most damaging light before it hits the cells behind them. Supplementing with these supplies more of what the eye already uses, instead of trying to feed in a foreign antioxidant.
So researchers built a second trial — AREDS2 — and asked a direct question: take the beta-carotene out, swap in lutein and zeaxanthin, and see what happens. This is the whole idea in one experiment. It's the real version of the tocotrienol question. Not "we assume a different form is safer" — but actually test it, head-to-head, with hard outcomes.
And here's what they found. First, on safety: lung cancer was 2.0% in the people getting the formula with beta-carotene, versus 0.9% in the people getting it without. Take the beta-carotene out, and that signal goes away [11].
And second, on whether the new formula still worked. In the direct comparison, the lutein-and-zeaxanthin formula came out at least as good as the old beta-carotene one for slowing the disease — slightly better, in fact [12]. So safer, and at least as effective. The whole field switched. Beta-carotene was dropped, and lutein and zeaxanthin became the standard formula.
Speaking of changes, there's been another one related to antioxidants and exercise that's come in just the past year on the back of new evidence.
If you're young and healthy and you train, taking big doses of antioxidant vitamins around your workouts is a mistake. Regular readers will have seen me cover this in detail — the short version is that exercise produces a brief burst of free radicals, and that burst is the signal your body reads to adapt. Mop it up with high-dose vitamin C and E, and you blunt the cellular machinery that exercise is trying to build [13]. Those free radicals from exercise aren't just background noise — researchers describe them as important to getting the full benefit of training [14].
And it's not only antioxidant vitamins. The same "don't blunt a useful signal" logic catches a couple of other popular things. Metformin, in people without diabetes, blunts some of the gains from training [15]. In a resistance-training study, the people on placebo built more muscle than the people on metformin [16]. And resveratrol did the same to the heart benefits of exercise in older men — the placebo group improved their fitness more than the resveratrol group did [17].
So if you train, adding any of these is likely the "more isn't better" mistake. For years, that made antioxidants look like a blanket bad idea for anyone exercising.
But here's the turn — and it's the population point. In older adults, the picture flips. As we age, the balance tips the other way: the system tips toward too much oxidative stress rather than too little. And in that group, antioxidants paired with exercise actually beat exercise alone [18]. I want to be straight about the size of that, though. The effects were small, and the authors themselves say the real-world significance still isn't clear. This isn't "older people should megadose antioxidants." It's a clean illustration of the idea: same intervention, opposite answer, depending on who you are. Young and training — leave the burst alone. Older, with the balance already tipped — a little support can help. And that flip is only true for the antioxidants; metformin and resveratrol stay in the don't-blunt-your-training bucket.
There's a smarter version of "support" worth a mention, which regular readers have seen me talk about — a precursor called GlyNAC. Rather than flooding the body with a finished antioxidant, you give it the raw materials to make its own, and let it self-regulate how much it needs. In older adults, that improved a range of aging markers [19].
Now one last thing — a frontier, where the evidence is thinner but genuinely interesting. Those same eye antioxidants, lutein and zeaxanthin, don't just collect in the eye. They build up in the brain too. And the amount in your eye can be measured easily, so researchers use it as a window onto the brain. The eye part is solid — these reliably raise the pigment in the macula [20]. In a 2026 trial in teenagers who used a lot of screens, attention and processing speed improved as well [21]. But I want to put a clear fence around the brain claim. The eye effect is solid. The brain effect is promising, not proven — the cognitive studies are small, and a striking amount of this research is funded by the companies that sell the ingredient. So it's a reasonable bet, not a settled fact.
To me, the lesson is simple. It isn't that antioxidants are bad. Rather, the right form, at the right dose, for the right person beats megadosing every single time. That's not a small point — it's the whole reason a carefully worked-out formula matters more than the instinct to just throw more at the problem. "More is better" is the thing that keeps backfiring.
So here's the practical takeaway. Don't megadose by default. When you see a label boasting a thousand percent of your daily vitamin E, or several thousand percent of vitamin C, treat that as a warning sign, not a selling point — it's the "more is better" instinct printed on a bottle. And before you trust what's in there at all, check the dose and the form against a third-party resource — consumerlab.com or labdoor.com will tell you what's actually inside and whether the amount is sensible. The right amount of the right form beats flooding the system.
And that burn trial from the start wasn't "vitamins are poison." It was the clearest possible picture of the wrong dose, in the wrong population.
References
1. https://doi.org/10.1001/jama.2026.10616
2. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
3. https://doi.org/10.1056/NEJMoa2200644
4. https://doi.org/10.1056/NEJM199605023341802
5. https://doi.org/10.1056/NEJM199404143301501
6. https://doi.org/10.1002/14651858.CD007176
7. https://doi.org/10.1001/jama.2011.1437
8. https://doi.org/10.1001/jama.2022.8970
9. https://doi.org/10.1093/nutrit/nuae061
10. https://doi.org/10.1001/archopht.119.10.1417
11. https://doi.org/10.1001/jama.2013.4997
12. https://doi.org/10.1001/jamaophthalmol.2013.7376
13. https://doi.org/10.1113/jphysiol.2013.267419
14. https://doi.org/10.1016/j.jshs.2024.05.001
15. https://doi.org/10.1111/acel.12880
16. https://doi.org/10.1111/acel.13039
17. https://doi.org/10.1113/jphysiol.2013.258061
18. https://doi.org/10.1038/s41598-025-16917-2
19. https://doi.org/10.1093/gerona/glac135
