Antioxidants and Cancer: Prevention Trial Results and Treatment Cautions
What randomized trials found when antioxidant supplements were tested to prevent cancer, why beta-carotene harmed smokers, and why people in cancer treatment should tell their oncology team first.
Content last updated . This page has not been medically reviewed.
If you are being treated for cancer
Tell your oncology team about every vitamin, mineral and antioxidant supplement you take or are thinking of taking, before you start or stop anything. NCCIH says antioxidants might reduce the effectiveness of cancer treatments that work by generating reactive oxygen-containing substances, and advises you to check with the health care providers managing your treatment. [1] The National Cancer Institute (NCI) likewise says people with cancer should inform their doctors about any dietary supplement they use. [2] Do not stop or change a prescribed treatment because of this page.
The short answer
Randomized trials of antioxidant supplements for preventing cancer did not show benefit, and some showed harm. After reviewing nine randomized controlled trials, the NCI concluded they did not provide evidence that dietary antioxidant supplements are beneficial in primary cancer prevention. [2] NCCIH says the current evidence does not support the idea that antioxidant supplements can prevent cancer, and that high doses of beta-carotene may increase the risk of lung cancer. [1]
None of this says that antioxidant-rich foods are unhelpful. Observational studies of foods and supplements have given mixed results and cannot adequately control for bias, which is why the NCI treats randomized trials as the stronger test. [2]
The key prevention trials
| Trial | Who | Tested | What it found |
|---|---|---|---|
| ATBC (Finland) | 29,133 male smokers aged 50 to 69 [3] | Alpha-tocopherol 50 mg/day and/or beta-carotene 20 mg/day for 5 to 8 years [3] | No reduction in lung cancer with alpha-tocopherol; higher lung cancer incidence with beta-carotene (an 18% change, 95% CI 3 to 36%) [3] |
| CARET (US) | 18,314 smokers, former smokers and asbestos-exposed workers [4] | 30 mg beta-carotene plus 25,000 IU retinol daily [4] | Relative risk of lung cancer 1.28 (95% CI 1.04 to 1.57); trial stopped 21 months early [4] |
| SELECT (US, Canada, Puerto Rico) | 35,533 men [5] | Selenium 200 mcg/day, vitamin E 400 IU/day (all-rac form), both, or placebo [5] | Vitamin E alone: more prostate cancer (hazard ratio 1.17, 99% CI 1.004 to 1.36) [5] |
| Physicians' Health Study I (US) | Male physicians | Beta-carotene 50 mg every other day for 12 years | No effect on cancer incidence, cancer mortality or all-cause mortality in smokers or non-smokers [2] |
| HOPE-TOO | People with vascular disease or diabetes | Vitamin E 400 IU/day, median 7 years | No difference in cancer incidence or cancer deaths [6] |
These are study amounts in specific groups. They are not advice, and each result applies to the form and population tested. The NCI's table also lists SU.VI.MAX in France, which combined several nutrients: it reported lower total cancer and prostate cancer incidence and all-cause mortality among men only, and increased skin cancer incidence among women only. [2] Mixed results like these are why single trials should not be over-read.
Pooled reviews
- USPSTF 2022 (community-dwelling, nonpregnant adults, US). Moderate certainty that the harms of beta-carotene outweigh the benefits for preventing cardiovascular disease or cancer. It recommends against beta-carotene or vitamin E for this purpose, and found the evidence insufficient for other single or paired nutrients. [7]
- Evidence review behind it. Beta-carotene, with or without vitamin A, was linked to a higher risk of lung cancer (odds ratio 1.20, 95% CI 1.01 to 1.42). [8]
- Cochrane 2012. No evidence to support antioxidant supplements for primary or secondary prevention; beta-carotene and vitamin E seemed to increase mortality. [9]
Smokers and asbestos-exposed workers
NCCIH says the strongest evidence of an increase in lung cancer risk with beta-carotene was in people at high risk, specifically smokers and people with occupational exposure to asbestos. [1] Details are on the beta-carotene, smokers and the ATBC and CARET trials page. The AREDS2 eye trial also saw more lung cancers with beta-carotene, mostly in former smokers, which is why the NEI advises smokers and former smokers away from that version. [10]
During chemotherapy or radiotherapy: what is known
The evidence is limited and mixed, so treat it as a caution, not a verdict.
- Chemotherapy. In SWOG S0221, 1,134 women with breast cancer on a chemotherapy trial were asked about supplements. Use of any antioxidant supplement (vitamins A, C and E, carotenoids, coenzyme Q10) before and during treatment was associated with more recurrence (adjusted hazard ratio 1.41; 95% CI 0.98 to 2.04; P = .06), a result that did not reach conventional statistical significance. [11] The authors said the findings were consistent with caution about supplements, other than a multivitamin, during chemotherapy. [11] NCCIH notes the result may be biased because participants chose their own supplements. [1]
- Radiotherapy. A 2025 systematic review found antioxidants may reduce radiation side effects, with vitamins C and E showing positive effects on oral mucositis, dry mouth and cardiac function. It also found multiple studies indicating that concurrent antioxidant use may impair tumor control, increase recurrence and reduce survival, and concluded that clinical recommendations are premature. [12]
- Animal studies. The NCI notes that in some preclinical studies antioxidants promoted tumor growth and spread in tumor-bearing mice. [2] Mouse findings do not prove the same happens in people.
- Vitamin C. NCCIH says vitamin C supplements may interact with cancer treatments such as chemotherapy and radiation therapy. [1]
Proper evidence not found in the sources read for a safe, proven way to use antioxidant supplements to protect treatment outcomes. Your oncology team can say whether a specific supplement fits your regimen. See antioxidants and medicines, integrative care during cancer treatment and talking with a health professional.
Frequently asked questions
Can antioxidant supplements prevent cancer?
Randomized trials did not show benefit; the NCI reviewed nine and found no evidence of benefit for primary prevention. [2]
Why was beta-carotene harmful in smokers?
We read what happened, not why. In ATBC and CARET, beta-carotene was linked to more lung cancer in smokers and asbestos-exposed workers. [3][4]
Did vitamin E raise prostate cancer risk?
In SELECT, men taking vitamin E 400 IU/day had more prostate cancer than those on placebo (hazard ratio 1.17). [5] This was one form (all-rac alpha-tocopheryl acetate) in older men and should not be generalized to every form or group.
Should I take antioxidants during chemotherapy?
Ask your oncology team first. NCCIH says check with the providers managing your treatment. [1]
Do antioxidant-rich foods have the same risk?
The NCI says the tested antioxidants may act differently as purified chemicals than in foods, which contain complex mixtures. Supplement results should not be carried over to foods. [2]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Other safety points
High-dose vitamin E may raise bleeding risk, which matters before procedures; see supplements before surgery. [1] If you are pregnant or nursing, or considering a supplement for a child, NCCIH says it is especially important to consult a health care provider. [1] Kidney and liver conditions: not described in the sources we read for this page; ask a clinician or pharmacist.
References
- National Center for Complementary and Integrative Health (NCCIH, US). Antioxidant Supplements: What You Need To Know. Read 2026-10-23.
- National Cancer Institute (US). Antioxidants and Cancer Prevention. Read 2026-10-23.
- ATBC Cancer Prevention Study Group. The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. N Engl J Med 1994. Read 2026-10-23.
- Omenn GS et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease (CARET). N Engl J Med 1996. Read 2026-10-23.
- Klein EA et al. Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA 2011. Read 2026-10-23.
- HOPE and HOPE-TOO Trial Investigators. Effects of long-term vitamin E supplementation on cardiovascular events and cancer (HOPE-TOO). JAMA 2005. Read 2026-10-23.
- US Preventive Services Task Force. Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer: Recommendation Statement. JAMA 2022. Read 2026-10-23.
- O'Connor EA et al. (evidence review for the USPSTF). Vitamin and Mineral Supplements for the Primary Prevention of Cardiovascular Disease and Cancer: Updated Evidence Report and Systematic Review. JAMA 2022. Read 2026-10-23.
- Bjelakovic G et al. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev 2012. Read 2026-10-23.
- National Eye Institute (US). AREDS/AREDS2 Clinical Trials, last updated October 22, 2025. Read 2026-10-23.
- Ambrosone CB et al. Dietary supplement use during chemotherapy and survival outcomes of patients with breast cancer enrolled in a cooperative group clinical trial (SWOG S0221). J Clin Oncol 2020. Read 2026-10-23.
- Limbrunner J et al. The influence of antioxidant supplementation on adverse effects and tumor interaction during radiotherapy: a systematic review. Clin Exp Med 2025. Read 2026-10-23.