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 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).
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Watch: Can supplements prevent cancer?
59 sec · Captioned · Trials found supplements don't prevent cancer — and high doses can backfire.
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This page is for anyone who takes, or is thinking about taking, vitamins or supplements to lower their cancer risk. It covers what the large trials found .
The claim
The claim is that vitamin, mineral, and antioxidant supplements lower your risk of getting cancer. That includes vitamin C, vitamin E, selenium, beta-carotene, and daily multivitamins.
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. Researchers tested it as a pill.
In the ATBC trial, lung cancer went up among male smokers taking beta-carotene supplements.
The CARET trial in the United States was stopped early. Participants taking beta-carotene had more lung cancer and more deaths from any cause.
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.
The SELECT trial in the United States was also stopped early. It found no reduction in prostate cancer. Later follow-up found more prostate cancer among men who took vitamin E alone.
Taking a nutrient as a supplement is not the same as eating it in food.
What this does not mean
It does not mean nutrients are bad. These trials tested supplements, not food.
It also does not mean supplements are harmless just because they are sold without a prescription. Ask your oncology team before taking any supplement during treatment, and bring a list of everything you take.
The bottom line
No supplement has been shown to prevent cancer in healthy people. Large trials found that beta-carotene supplements 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 ask your clinician what fits your situation.
Sources
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. In ATBC, lung cancer went up among male smokers taking it. CARET was stopped early because participants taking beta-carotene had more lung cancer and more deaths from any cause.
Are supplements safe during cancer treatment?
Do not assume so. Ask your oncology team before taking any supplement during treatment, and bring a full list of everything you take.
Questions to ask your doctor
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Your next step
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Written by: Cancer ExplainedSources last checked: 2026-10-02 what this meansLast updated: 2026-10-02Next 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, and this 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 then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
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.
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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, and this 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 then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. 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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