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Antioxidant supplements — do they actually work?

One of the biggest gaps between marketing and evidence in the supplement aisle. The short version: antioxidant-rich food is great — isolated high-dose antioxidant pills mostly aren’t, and can even backfire.

Reviewed by Bodil Isaksson, Licensed Biomedical Scientist (Sweden)Last reviewed July 2026Supplement guide

SupplementsAntioxidantsEvidence

“Antioxidant” is one of the most powerful words in supplement marketing. But when isolated antioxidants are put to the test in large trials, the results are humbling — and occasionally worrying. Here is the honest picture, and where a few targeted antioxidants still earn their place.

Key takeaways

  • A Cochrane review of 78 trials (~296,000 people) found antioxidant supplements did not lower mortality — and beta-carotene, vitamin A and vitamin E may raise it.1
  • High-dose vitamin C + E can blunt the adaptations to exercise (mitochondrial biogenesis) — a real downside for athletes.2
  • Some free-radical activity is useful signalling; mopping it all up with megadoses can backfire.3
  • A colourful diet beats pills. A few targeted antioxidants (CoQ10, alpha-lipoic acid) have genuine niche uses.

What antioxidants are

Antioxidants neutralise reactive oxygen species (ROS) — the “free radicals” produced by normal metabolism. Crucially, the body already runs its own powerful antioxidant system (glutathione, superoxide dismutase, catalase), topped up by dietary antioxidants (vitamin C and E, carotenoids, and thousands of polyphenols in plants). ROS aren’t purely “bad” either — they act as signals that drive adaptation, immunity and repair.

The disappointing pill evidence

On paper, swallowing antioxidants to fight ageing and disease sounds obvious. In practice, the large trials have been a let-down.

No mortality benefitThe Cochrane meta-analysis of 78 randomised trials found antioxidant supplements did not reduce death overall.1
Some raised riskBeta-carotene increased lung cancer in smokers; high-dose vitamin E has been linked to higher mortality and prostate-cancer risk.1
Food ≠ pillsThe benefit of antioxidant-rich foods doesn’t transfer to isolated high-dose extracts — whole foods deliver a balanced matrix, not a megadose of one compound.

When they can harm

Blunting exerciseIn a controlled trial, 1000 mg vitamin C + 235 mg vitamin E daily blunted the endurance-training rise in mitochondrial proteins — the very adaptation you train for.2
AthletesReviews warn that high-dose antioxidants can hamper mitochondrial biogenesis, muscle hypertrophy and insulin-sensitivity gains.3 Time big doses away from training blocks, or skip them.
SmokersAvoid beta-carotene supplements entirely.1
CoQ10 / ubiquinolThe best case of the group: modest evidence in heart failure and possibly statin-related muscle symptoms; safe. A reasonable targeted choice.
Alpha-lipoic acidSome evidence for diabetic nerve pain and blood sugar; a defined niche.
AstaxanthinA carotenoid with promising but small studies for skin and eye; low-risk.
ResveratrolHeavily hyped, but poorly absorbed and human results are weak — underwhelming.
Polyphenols (curcumin, EGCG, quercetin, pycnogenol)Act more as signalling / anti-inflammatory compounds than blunt antioxidants; mixed, generally modest evidence.
Glutathione / NACSupport the body’s own master antioxidant — see our NAC guide. More promising than most direct antioxidant pills.

Individual antioxidant guides

Dedicated, evidence-based pages for each of the popular antioxidant supplements:

CoQ10CoQ10Alpha-lipoic acidAlpha-lipoic acidAstaxanthinAstaxanthinLutein & zeaxanthinLutein & zeaxanthinLycopeneLycopeneGlutathioneGlutathioneCurcuminCurcuminQuercetinQuercetinGreen tea (EGCG)Green tea (EGCG)Grape seed & PycnogenolGrape seed & PycnogenolCitrus bioflavonoidsCitrus bioflavonoidsMelatoninMelatoninResveratrolResveratrolFisetinFisetin

How to actually get them

Eat the rainbow. Berries, leafy greens, herbs and spices, colourful vegetables, coffee, tea, cocoa and extra-virgin olive oil deliver a broad, balanced spread of antioxidants in the amounts evolution tuned us for. If you use a targeted supplement (CoQ10, ALA), pick one with a clear reason and a sensible dose — not a shotgun “antioxidant complex” megadose.

Bottom line: food-source antioxidants are excellent; isolated high-dose antioxidant pills are, at best, unproven and, at worst, harmful — a few targeted ones (CoQ10, alpha-lipoic acid) aside.

References

Adult research summary for education, not a prescription. These are food supplements, not treatments for disease.

  1. Bjelakovic G, et al. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev 2012. pmc.ncbi.nlm.nih.gov
  2. Paulsen G, et al. Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind, randomised, controlled trial. J Physiol 2014. pmc.ncbi.nlm.nih.gov
  3. Potential harms of supplementation with high doses of antioxidants in athletes. 2022. pmc.ncbi.nlm.nih.gov · See also NCCIH, Antioxidant Supplements: What You Need To Know. nccih.nih.gov

This article summarises nutrition science for education. It is not a substitute for individual medical advice; consult a professional before starting a supplement, in pregnancy, or alongside medication.