Beta-carotene
Also called: betacarotene, provitamin A.
Last reviewed 2026-09-16. How this works.
When to call your team — there is nothing to watch for
Whatever you are taking or thinking of taking, the people treating you can only weigh it if they know about it. That is true when nothing has been written down here, and it is most true then.
The harm recorded on this page is a raised chance of developing cancer over years. It is not something a person can feel happening, so there are no signs to watch for, and that is the point rather than an omission. What it is a reason for is telling your team what you take.
This block is about what to watch for, and it is not all this page holds: what has been recorded about harm is below. Nothing in this block is an all-clear for a question it does not mention.
Preventing lung cancer Grade E
Human evidence points the wrong way.
Harm has been recorded in people for this claim. The grade measures how strong the evidence for benefit is; it says nothing about the harm, and the two are read from different parts of this page.
A big trial of this supplement was stopped early because the people taking it were getting more lung cancer.
A trial stopped early: more lung cancer and more deaths in the supplemented group.
The harm
The CARET trial gave beta-carotene and retinyl palmitate to 18,314 people at high risk of lung cancer through smoking or asbestos exposure. It was stopped 21 months early because the supplemented group had 28 percent more lung cancer, 17 percent more deaths, and higher cardiovascular mortality than placebo.2
Follow-up after the trial ended found the relative risks for lung cancer and for death from any cause remained above one throughout. The harm did not stop when the supplement did.2
A Finnish trial in 29,133 male smokers had already pointed the same way, and a later pooling of eight studies across 167,141 participants confirmed it: beta-carotene supplementation was associated with an increased risk of lung cancer, and the association was stronger among smokers and asbestos workers.13
The claim
The claim was that beta-carotene, the pigment that makes carrots orange and that tracks with lower cancer rates in people who eat more vegetables, would prevent lung cancer if given as a supplement.
What it does
The reasoning was sound and the observational evidence was strong. This entry is in the book because it is the clearest example of what happens when a plausible mechanism and a consistent observational signal are finally put to a randomised test.
The evidence
The scope of the harm signal is worth stating. The trial in a population that was largely not current smokers found no significant benefit and no significant harm, so the danger is concentrated in exactly the group the supplement was meant to help.43
The studies this rests on
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CARET, beta-carotene and retinyl palmitate in people at high risk of lung cancer2
A randomised trial, double blind, measured a clinical outcome, 18314 participants.
stopped early for more lung cancer and more deaths in the supplemented group.
relative risk 1.36, interval 1.07 to 1.73. weighted lung cancer incidence; weighted lung cancer mortality 1.59, interval 1.13 to 2.23
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Pooled studies of beta-carotene and lung cancer3
A meta-analysis, summarising randomised and observational studies together, measured a clinical outcome, 167141 participants.
increased risk of lung cancer, stronger among smokers and asbestos workers.
relative risk 1.16, interval 1.06 to 1.26. among smokers and asbestos workers 1.21, interval 1.08 to 1.35
What to ask
Are any of the supplements I take ones you would want me to stop while I am being treated?
The dish-to-person gap
The register holds no concentration comparison for beta-carotene. This entry rests on randomised outcome trials.
Interactions
The register holds no measured interaction between beta-carotene and a cancer treatment class. Chapter 16 of the book covers supplement interactions in general, and an empty list here means nobody has measured this one.
Nobody having looked is not the same as nothing being there. That is what this line says and all it says.
The whole interaction list, and how to turn it into a pharmacy review request.
Find a trial instead
The question here has been answered by two large randomised trials, one of which was stopped early.
References
The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. New England Journal of Medicine 1994;330:1029-1035.
doi:10.1056/NEJM199404143301501 · PubMed 8127329
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 17 note 1.
The Beta-Carotene and Retinol Efficacy Trial (CARET).
No persistent identifier recorded.
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 17 note 17.
Role of beta-carotene in lung cancer primary chemoprevention: a systematic review with meta-analysis and meta-regression.
No persistent identifier recorded.
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 17 note 2.
Hennekens CH, Buring JE, Manson JE, et al. Lack of effect of long-term supplementation with beta carotene on the incidence of malignant neoplasms and cardiovascular disease. New England Journal of Medicine 1996;334:1145-1149.
No persistent identifier recorded.
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 17 note 3. The author string is abbreviated in the source that was read and has not been expanded.