The short answer
Large randomized trials have not shown that vitamin, mineral or antioxidant supplements prevent cancer. High-dose beta-carotene increased lung cancer in smokers, and vitamin E increased prostate cancer.
NCI's review of nine randomized trials found no evidence that dietary antioxidant supplements are beneficial in preventing cancer.
The USPSTF recommends against beta-carotene and vitamin E for preventing cancer or heart disease (grade D), and finds the evidence insufficient to judge multivitamins or most single nutrients (grade I).
Beta-carotene increased lung cancer in the ATBC trial of male smokers, and the CARET trial in smokers and asbestos-exposed workers was stopped early for more lung cancer and more deaths from any cause.
In trials in people who smoke or were exposed to asbestos, USPSTF reports an 18% higher lung cancer risk with beta-carotene (RR 1.18, 95% CI 1.03 to 1.36).
Watch: Can supplements prevent cancer?
59 sec · Captioned · Trials found supplements don't prevent cancer — and high doses can backfire.
Educational only — this video explains general report language and is not medical advice. Only your care team can say what a result means for you.
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The full explanation.
The claim
Vitamin, mineral and antioxidant supplements lower your risk of getting cancer. That means vitamin C, vitamin E, selenium, beta-carotene, or a daily multivitamin.
What the evidence shows
This claim has been tested head-on, in large randomized trials. The answer has been consistently disappointing. NCI reviewed nine randomized controlled trials of antioxidant supplements. It concluded that they did not provide evidence that dietary antioxidant supplements are beneficial in primary cancer prevention.
In 2022 the US Preventive Services Task Force landed in the same place. It found the evidence insufficient to judge multivitamins for preventing cancer or heart disease. It also found the evidence insufficient to judge most single or paired nutrients. For two supplements it went further, and recommended against them outright.
The example everyone should know: beta-carotene
Beta-carotene is the pigment that makes carrots orange. People who eat more of these vegetables get less lung cancer. So researchers tested the pill.
The ATBC trial gave middle-aged male smokers in Finland beta-carotene, vitamin E, both or neither. Lung cancer went up among the men taking beta-carotene.
The CARET trial in the United States tested beta-carotene plus retinol. The people in it were smokers, and people exposed to asbestos at work. It was stopped early. The supplement group had more lung cancer, and more deaths from any cause. In extended follow-up, those higher risks persisted.
The USPSTF reviewed the trials in people who smoke or were exposed to asbestos. It reports an 18% higher lung cancer risk with beta-carotene (RR 1.18, 95% CI 1.03 to 1.36). It gives beta-carotene and vitamin E a grade D: it recommends against using them to prevent cancer or heart disease.
SELECT tested selenium and vitamin E in men aged 50 and older. It was also stopped early. It found no reduction in prostate cancer, and more prostate cancers among the men taking vitamin E alone.
That is the pattern. A nutrient that looks protective in food does not become a protective drug in a capsule. At high doses it can even push the other way.
What this does not mean
It does not mean nutrients are bad, or that food does not matter. Diets high in vegetables, fruit, whole grains and fiber are associated with lower cancer risk. But food is not the same thing as an isolated extract at many times the dietary dose.
It does not mean supplements are never appropriate. Correcting a documented deficiency is a real medical use. So is folic acid in pregnancy, and so are supplements prescribed after certain surgeries. Those are treatments for a specific problem. They are not cancer prevention.
It also does not mean supplements are harmless just because they are sold without a prescription. In the US they are not reviewed for effectiveness before sale. Some interact with chemotherapy, targeted drugs, immunotherapy or radiation. And high-dose antioxidants during active treatment are an open safety question. Your oncology team will want to weigh in on that.
What does lower risk
The prevention steps with real evidence behind them are unglamorous. Do not smoke, and quit if you do. Keep alcohol low. Stay active, and at a weight that is healthy for you. Protect your skin from the sun. Get the HPV and hepatitis B vaccines. And do the screening tests recommended for your age and history. Those change outcomes in a way no capsule has.
The bottom line
No supplement has been shown to prevent cancer in healthy people. Two well-run trials found that high-dose beta-carotene increased lung cancer in smokers. Bring a full list of everything you take, with brands and doses, to your next appointment. That matters most if you are in cancer treatment, or about to start. Then let your clinician tell you what fits your situation.
Sources
Words to know
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Common questions
Is there any supplement proven to prevent cancer in healthy people?
No. Across large randomized trials of antioxidants, vitamins and minerals, none has been shown to reduce cancer risk in the general population. The USPSTF found the evidence insufficient even for ordinary multivitamins, and recommends against beta-carotene and vitamin E specifically.
How can a supplement make cancer risk worse?
The clearest example is beta-carotene. Two trials tested it in people at high lung cancer risk. In ATBC, lung cancer went up among male smokers taking it. In CARET, the trial was stopped early because smokers and asbestos-exposed workers taking beta-carotene had more lung cancer and more deaths. High doses of an isolated nutrient behave differently in the body than the same nutrient in food.
If vegetables lower cancer risk, why does the pill not work?
Food delivers hundreds of compounds together, at modest doses, in a package your body evolved to handle. A supplement isolates one compound, often at many times the dietary amount. The trials show that difference matters, and it is one reason nutrition advice keeps pointing back to whole foods.
Are supplements safe during cancer treatment?
Not automatically. Some supplements interact with chemotherapy, targeted therapy, immunotherapy or radiation, and the effect of high-dose antioxidants during treatment is an open safety question. Bring a full list of everything you take, including doses, to your oncology team so they can check it against your regimen.
Are supplements tested before they are sold?
Not for effectiveness. In the US, dietary supplements are not reviewed by the FDA for whether they work before they go on sale, and manufacturers are responsible for their own safety and labeling. A product on a pharmacy shelf has not necessarily been shown to do anything.
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Your next step
What the evidence shows about common cancer claims.
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Written by: Cancer ExplainedSources last checked: 2026-08-13 what this meansLast updated: 2026-08-18Next planned review: 2027-01-30
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
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High-risk topic — talk to your care team. This topic can involve urgent, individual medical decisions. This page is general education only: it cannot tell you whether your situation is an emergency or what you personally should do. Follow your oncology team's instructions and contact them for individual guidance.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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