Do not take antioxidant supplements—beta carotene, vitamin E, or vitamin A—to prevent cancer
These supplements can do more than fail to help. Across 78 trials involving almost 300,000 people, some analyses found slightly higher mortality. Two large trials in smokers or people exposed to asbestos found 18%–28% more lung cancer and 8%–17% higher mortality with the tested beta-carotene regimens. Smokers and people exposed to asbestos should be especially cautious.
What it takes
About RMB 0.5–2 a day. For smokers, the more serious cost is increased lung-cancer risk.
What you may gain
A Cochrane review combined 78 randomized controlled trials involving 296,707 people. Overall mortality with antioxidant supplements had an RR of 1.02 (95% CI 0.98–1.05); an RR of 1 means no difference. Restricting the analysis to trials at lower risk of bias produced an RR of 1.04 (1.01–1.07), a small increase. The separate estimates were 1.05 (1.01–1.09) for beta carotene and 1.03 (1.00–1.05) for vitamin E. ATBC enrolled 29,133 male smokers; 20 mg of beta carotene daily increased lung-cancer incidence by 18% (3%–36%) and overall mortality by 8% (1%–16%). CARET enrolled 18,314 smokers or people exposed to asbestos. Lung-cancer risk rose by about 28%, RR 1.28 (1.04–1.57), and all-cause mortality by about 17%, RR 1.17 (1.03–1.33). “Antioxidants prevent aging, and preventing aging prevents cancer” sounds plausible at every step, but plausibility is not evidence of benefit.
Context & considerations
In 2022, the USPSTF gave beta carotene and vitamin E a D recommendation for this preventive use, meaning it recommended against them. Harm has already been demonstrated in smokers and people exposed to asbestos. This does not apply to antioxidants naturally present in vegetables and fruit; keep eating those foods.
Research & references
Bjelakovic G et al. (2012). Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev. https://doi.org/10.1002/14651858.CD007176.pub2; The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group (1994). The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. NEJM. https://doi.org/10.1056/NEJM199404143301501; Omenn GS et al. (1996). Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. NEJM. https://doi.org/10.1056/NEJM199605023341802.