Vitamin E and beta-carotene, taken as antioxidant supplements, are included in this encyclopedia precisely because the longevity evidence points the wrong way. A Cochrane review of 78 randomized controlled trials, covering 296,707 participants, found both supplements associated with a small but statistically significant increase in all-cause mortality, particularly at doses above the RDA (recommended dietary allowance). A separate meta-regression confirmed specific dose thresholds where this harm appears. Below-RDA doses didn’t show harm, but also showed no benefit, meaning there's no dose range at which supplementing with these two compounds has been shown to actually help. That distinction comes from a later meta-regression by the same group, which found beta-carotene and vitamin E above the RDA significantly increased mortality and concluded that information on doses below the RDA is lacking. Lacking information is not the same as evidence of safety.
- A Cochrane review of 78 RCTs (296,707 participants) found a small but statistically significant increase in all-cause mortality.
- Harm specifically appeared above the RDA, beta-carotene above 9.6mg/day and vitamin E above 15mg/day.
- Below-RDA doses showed no harm, but also no benefit, there's no dose range where supplementing clearly helps.
- Earlier landmark trials (ATBC, CARET) found beta-carotene increased lung cancer mortality risk specifically in smokers.
The Cochrane review of antioxidant supplements
The review covered 78 trials and 296,707 participants. Across all of them, in a random-effects model, there was no significant effect on mortality: RR 1.02, 95% CI 0.98 to 1.05.
Restricted to the 56 trials at low risk of bias, mortality significantly increased: RR 1.04, 95% CI 1.01 to 1.07. Beta-carotene ran at RR 1.05 (95% CI 1.01–1.09) across 26 such trials, vitamin E at RR 1.03 (95% CI 1.00–1.05) across 46. Vitamin A, vitamin C and selenium did not significantly affect mortality.
The gap between those two results is the interesting part. The harm signal appears when the weaker trials are excluded, which is the opposite of how bias usually flatters a finding.
Cochrane reviews are widely regarded as among the most rigorous, systematically conducted forms of evidence synthesis in medicine, combining data across many independent trials using standardized methodology specifically designed to minimize bias. A Cochrane review pooling 78 randomized controlled trials and 296,707 participants, a genuinely enormous sample size relative to almost anything else covered in this encyclopedia, found that beta-carotene and vitamin E supplementation were associated with a small but statistically significant increase in all-cause mortality.
The word "small" matters here, this isn't a dramatic, large-magnitude increase in risk, but "statistically significant" means the finding is very unlikely to be due to chance alone given the scale of the pooled data. A separate meta-regression, a statistical technique for examining how effect size changes with dose across many trials, further confirmed that this harm tracked specifically with dose, reinforcing that this isn't a fluke finding from a single outlier trial but a pattern that holds up across a large, carefully analyzed body of evidence.
Where the harm shows up
The meta-regression specifically identified dose thresholds, beta-carotene above 9.6mg/day and vitamin E above 15mg/day, above which mortality risk increased significantly. Both of these thresholds sit above typical RDA levels, meaning the harm isn't associated with ordinary dietary intake of these nutrients from food, it's specifically tied to concentrated supplemental doses exceeding what a normal diet would typically provide.
This is a genuinely different kind of finding than most entries in this encyclopedia, where the usual honest caveat is "the evidence for benefit is weaker than marketed." Here, the more directly relevant caveat is that supplementing above these specific thresholds is associated with measurable harm, not simply an absence of benefit.
Below-RDA vs. above-RDA
| Below-RDA Intake | Above-RDA Supplemental Doses | |
|---|---|---|
| Associated harm | No | Yes, statistically significant increase in mortality |
| Associated benefit | No | No |
| Typical source | Normal varied diet | Concentrated supplements |
| Recommended target | RDA from food | Not supported by evidence |
Trial results by supplement and by risk of bias. The harm signal appears in the low-risk-of-bias subset, not across all trials.
There is no dose range in this table where supplementing beyond what a normal diet provides shows a demonstrated benefit, this is a rare, clean case where the evidence-supported answer is simply not to supplement with concentrated doses of these two compounds specifically.
The lung cancer trials
Beyond the Cochrane review, earlier landmark trials specifically examined beta-carotene supplementation in smokers, a population already at elevated baseline risk for lung cancer. The ATBC and CARET trials, both large, well-designed randomized controlled trials conducted in the 1990s, found that beta-carotene supplementation increased lung cancer mortality risk specifically in smokers, a striking, unexpected finding at the time given that beta-carotene was originally hypothesized to be protective based on earlier observational research.
This history is part of why beta-carotene supplementation in particular carries a longer track record of caution among researchers than many other antioxidant supplements, the harm signal here isn't a brand-new 2025 discovery, it's a pattern that has been building across multiple independent, well-designed trials over several decades.
Safety
This is one of the clearest examples in supplement research of "more isn’t better." If you eat a normal, varied diet, you're very likely already getting adequate amounts of both vitamin E and beta-carotene from food, without needing a concentrated supplement at all. Given the specific mortality and cancer-risk findings covered above, this is a genuine case where avoiding supplementation above RDA levels is the evidence-supported choice, not an overly cautious one.
Common misconceptions
"Antioxidant supplements are always beneficial or at worst neutral." This entry is a direct counterexample, a large, rigorous Cochrane review found a statistically significant increase in mortality above RDA doses, "antioxidant" doesn't automatically mean "safe at any dose."
"If a little is fine, more must be better." The data shows the opposite, below-RDA intake showed no harm, but doses above specific thresholds showed increased mortality risk, this is a case where more is measurably worse, not simply unhelpful.
"The lung cancer finding only applies to smokers, so it's irrelevant to me." The ATBC and CARET findings were specific to smokers, but the Cochrane review's mortality finding applies more broadly across the general population studied, worth taking both findings seriously rather than assuming only the smoker-specific one matters.
An entry about a harm finding
Most articles default to listing potential benefits. These two are here precisely because the evidence points the other way.
Below the RDA and above it are entirely different situations. Correcting a deficiency helps. Pushing intake well beyond it is where the harm signal appears.
It is the clearest illustration on this site that more antioxidants isn’t automatically better, and can occasionally be worse.
The app flags genuine harm findings clearly, not just weak-evidence supplements.
Sources
Key references for the claims on this page. Where a figure is attributed to a specific study or body, it is named here.
- Bjelakovic G, Nikolova D, Gluud C. Meta-regression analyses, meta-analyses, and trial sequential analyses of the effects of supplementation with beta-carotene, vitamin A, and vitamin E singly or in different combinations on all-cause mortality: do we have evidence for lack of harm? PLOS ONE. 2013;8(9):e74558. The source of the below-RDA versus above-RDA distinction. DOI
- 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. Beta-carotene supplementation increased lung cancer incidence.
- Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. New England Journal of Medicine, 1996. The CARET trial was stopped early for harm.
- Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database of Systematic Reviews. The review underlying the harm signal described here.
Frequently asked
Do these supplements increase mortality risk?
A Cochrane review of 78 RCTs and 296,707 participants found a small but statistically significant increase in all-cause mortality above RDA doses.
Is there a safe dose?
Below-RDA doses showed no harm but also no benefit. Harm appeared above 9.6mg/day beta-carotene and 15mg/day vitamin E.
Does beta-carotene increase cancer risk?
In earlier landmark trials (ATBC and CARET), it increased lung cancer mortality risk specifically in smokers.
Should I get these nutrients from food instead?
Yes, a normal varied diet very likely already provides adequate amounts, without the risks associated with concentrated supplemental doses.