Antioxidant Safety and Marketing Claims: High Doses, Smoking, Cancer Treatment and ORAC

Smoking and beta-carotene

If you smoke or used to, avoid high-dose beta-carotene supplements. In a trial of 29,133 male smokers, 20 mg a day was linked with 18% more lung cancer. [1] In CARET (18,314 smokers, former smokers and asbestos-exposed workers), beta-carotene 30 mg plus vitamin A 25,000 IU was linked with a relative risk of lung cancer of 1.28 and the trial was stopped early. [2] In AREDS2, lung cancer occurred in 2.0% with beta-carotene versus 0.9% without, mostly in former smokers. [3] The NEI advises current and former smokers to use the AREDS2 formula, which has no beta-carotene. [4] See carotenoids.

Cancer treatment

Some cancer treatments work by generating reactive oxygen substances, so antioxidants might reduce their effectiveness. [5] In a study of 1,134 women with breast cancer, any antioxidant supplement use during chemotherapy was linked with higher risks of recurrence and death, though the participants chose their own supplements, so the result may be biased. [5] The National Cancer Institute says some trials found worse outcomes with antioxidants during treatment, especially in smokers, and that these supplements should be used with caution. [6] A 2025 review of radiotherapy found antioxidants may reduce side effects but could compromise treatment, concluding recommendations are premature. [7] The NCCIH also says vitamin C supplements may interact with cancer treatments. [5] Tell your oncology team about everything you take.

High doses

• Vitamin E: high doses may increase bleeding risk and interact with anticoagulant or antiplatelet medicines. [5] SELECT linked vitamin E 400 IU to more prostate cancer (hazard ratio 1.17). [8] The NHS (UK) says 540 mg (800 IU) or less a day of supplements is unlikely to cause harm, while noting its page was last reviewed in 2020. [9] See vitamin E.
• Vitamin C: high doses can cause diarrhea, nausea and stomach cramps, and can worsen iron overload in hemochromatosis. [5] See vitamin C.
• Vitamin A: the NHS says more than an average of 1.5 mg a day over many years may weaken bones. [10]
• Combinations: in one study an antioxidant combination reduced the cholesterol-lowering effect of two drugs. [5]
• Overall: a Cochrane review of 78 trials found beta-carotene and vitamin E seemed to increase mortality. [11]

ORAC and similar marketing numbers

ORAC is a laboratory score of antioxidant capacity. A 2012 trade-press report says the USDA removed its ORAC database, citing routine misuse by manufacturers and the fact that laboratory results cannot be extrapolated to effects in the body. [12] High-ORAC claims on labels tell you little about what happens in the body. Label: marketing claim.

Biomarkers versus outcomes

A biomarker is a lab number. Oral glutathione raised blood glutathione in one trial, and astaxanthin lowered a blood marker in a meta-analysis, but neither result shows prevented disease. [13][14] Berberine lowers HbA1c, yet that is not the same as fewer complications. [15] Ask: what outcome, in whom, over how long?

"Anti-aging" and disease-prevention promises

No supplement in this category has shown it slows human aging. The best-tested approach, a Cochrane review, found no evidence to support antioxidant supplements for prevention. [11] See NAD, NMN and longevity claims. Phrases like "cures", "detox" or "prevents cancer" on a label are red flags; see evaluating safety claims.

What to do

Use the lowest useful amount for a defined reason, avoid stacking products with the same ingredient, and review them with a clinician: amounts and duplicate ingredients, medication interactions and surgery.