Question explored with the scientific record
Are antioxidants helpful to health. If so, which are best
The answer depends heavily on which antioxidant and who takes it. Most large trials show no net benefit; some show clear harm.
The most reliable evidence comes from large, randomized, placebo-controlled trials. The SU.VI.MAX study found that a low-dose combination of antioxidants (vitamin C, vitamin E, beta-carotene, selenium, zinc) reduced cancer incidence in men during the supplementation period, with a relative risk of 0.71 [1]. However, that benefit disappeared entirely in the 5-year follow-up after supplements stopped, and women saw no benefit at any point [1]. This pattern—a temporary effect that vanishes—is not what you want from a health intervention.
Far more concerning are the beta-carotene trials. Two large, high-quality randomized trials—ATBC and CARET—found that beta-carotene supplements increased lung cancer incidence and deaths in smokers and asbestos-exposed workers [3]. In ATBC, the relative risk for lung cancer was 1.18 [3]. In CARET, it was 1.28 [3]. A systematic review confirmed that beta-carotene supplementation increases the risk of lung cancer (relative risk 1.13) and stomach cancer (1.34) in these high-risk groups [6]. For a healthy non-smoker, the Physicians' Health Study found no harm but also no benefit from beta-carotene over more than 12 years [3].
Vitamin E shows a dose-dependent risk. A meta-analysis of 19 trials found that high-dose vitamin E (400 IU/day or more) increased all-cause mortality by about 4% [2]. A larger 2011 meta-analysis of 57 trials found no overall effect on mortality [5], but the high-dose signal from the more detailed 2005 analysis is worth noting.
| Antioxidant | What the trials show | Best evidence |
|---|---|---|
| Beta-carotene (smokers / asbestos-exposed) | Increases lung cancer and death | ATBC, CARET trials [3][7] |
| Beta-carotene (healthy non-smokers) | No benefit, no harm | Physicians' Health Study [3] |
| Vitamin E (high dose ≥400 IU/day) | May increase all-cause mortality | Miller 2005 meta-analysis [2] |
| Low-dose multi-antioxidant (men) | Reduced cancer during use only | SU.VI.MAX trial [1] |
| Selenium + CoQ10 (elderly) | Reduced cardiovascular death | Alehagen 2015 trial [4] |
The one standout is a 2015 trial of selenium (200 mcg) plus coenzyme Q10 (200 mg) in elderly Swedish adults. Over 10 years of follow-up, supplementing for just 4 years reduced cardiovascular mortality by about 50% [4]. This result needs replication.
My call: For healthy people not deficient in any micronutrient, the evidence does not support routine antioxidant supplementation—and beta-carotene is clearly harmful for smokers and asbestos-exposed people. The selenium/CoQ10 combination shows real promise for older adults but is a single trial. Confidence: moderate that the general recommendation should be to get antioxidants from food, not pills, unless a specific deficiency or targeted high-risk population (like older adults for selenium/CoQ10) is being addressed.
Sources used 7
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Incidence of cancers, ischemic cardiovascular diseases and mortality during 5‐year follow‐up after stopping antioxidant vitamins and minerals supplements: A postintervention follow‐up in the SU.VI.MAX Study
A randomized, double-blind post-trial follow-up of the SU.VI.MAX study shows that low-dose antioxidant supplementation reduced cancer incidence and all-cause mortality in men during active supplementation, but these benefits disappeared during the 5-year post-intervention period…
DOI: 10.1002/ijc.25201 -
Meta-Analysis: High-Dosage Vitamin E Supplementation May Increase All-Cause Mortality
A dose–response meta-analysis of 19 randomized trials (135,967 participants) finds that high-dose vitamin E supplementation (≥400 IU/d for ≥1 year) may increase all-cause mortality, while lower doses show no clear harm or benefit.
DOI: 10.7326/0003-4819-142-1-200501040-00110 -
CHEMOPREVENTION OF LUNG CANCER: The Rise and Demise of Beta-Carotene
Beta-carotene chemoprevention trials for lung cancer, justified by promising epidemiologic evidence, not only showed no benefit in ATBC and CARET but significantly increased lung cancer incidence and mortality, leading to revised public health recommendations.
DOI: 10.1146/annurev.publhealth.19.1.73 -
Reduced Cardiovascular Mortality 10 Years after Supplementation with Selenium and Coenzyme Q10 for Four Years: Follow-Up Results of a Prospective Randomized Double-Blind Placebo-Controlled Trial in Elderly Citizens
A 4-year randomized, double-blind, placebo-controlled trial of elderly Swedish citizens found that selenium and coenzyme Q10 supplementation reduced cardiovascular mortality by about 50% over 10 years, with persisting protection after cessation and beneficial effects across seve…
DOI: 10.1371/journal.pone.0141641 -
Vitamin E and All-Cause Mortality: A Meta-Analysis
A comprehensive random-effects meta-analysis of 57 randomized trials (n≈246,371 participants) assessing vitamin E supplementation in adults finds no overall effect on all-cause mortality (RR ≈ 1.00, 95% CI 0.98–1.02), with no dose-response and no significant mortality risk acros…
DOI: 10.2174/1874609811104020158 -
Beta‐carotene supplementation and cancer risk: a systematic review and metaanalysis of randomized controlled trials
This systematic review and meta-analysis of randomized controlled trials found that beta-carotene supplementation does not reduce cancer incidence and may increase the risk of lung and stomach cancers, particularly in smokers and asbestos workers.
DOI: 10.1002/ijc.25008 -
The Carotene and Retinol Efficacy Trial (Caret)
The Carotene and Retinol Efficacy Trial (CARET) found that daily supplementation with beta-carotene and retinyl palmitate did not reduce lung cancer incidence in high-risk populations and was associated with increased risk of lung cancer and overall mortality.
DOI: 10.1002/9780471462422.eoct053