Don’t take antioxidant supplements to prevent cancer (beta-carotene, vitamin E, vitamin A)

Cost: Roughly 0.5 to 2 yuan per day. For smokers, the real cost is a higher risk of lung cancer.
In plain terms: This isn’t just ineffective — it’s actually harmful. A review of 78 randomized controlled trials involving nearly 300000 people found that those taking antioxidant supplements had a slightly higher overall mortality rate. Two large trials focused on smokers showed that beta-carotene raised the likelihood of developing lung cancer by 18% to 28% and increased death rates by 8% to 17%. Smokers and people exposed to asbestos should absolutely avoid these supplements.
Benefit: Cochrane analyzed 78 randomized controlled trials with 296707 participants. Overall, those taking antioxidant supplements had a relative risk of death of 1.02 (a value of 1 means no difference; the 95% confidence interval was 0.98–1.05). When only higher-quality trials were considered, the relative risk rose to 1.04 (1.01–1.07). Specifically, beta-carotene raised the risk to 1.05 (1.01–1.09) and vitamin E to 1.03 (1.00–1.05). The ATBC trial followed 29133 male smokers who took 20 mg of beta-carotene daily; it found a 18% higher rate of lung cancer (range 3%–36%) and an 8% higher overall mortality rate (range 1%–16%). The CARET trial included 18314 smokers and asbestos-exposed individuals; it showed a 28% higher risk of lung cancer (relative risk 1.28, 1.04–1.57) and a 17% higher risk of all-cause death (relative risk 1.17, 1.03–1.33). The perception that these supplements are beneficial stems from the flawed logic that antioxidants prevent aging, which in turn prevents cancer — each step of this chain seems intuitive at first glance.
Evidence grade: A
Sources: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
Notes: The US Preventive Services Task Force, the official US body that evaluates preventive measures, assigned a grade D to beta-carotene and vitamin E in 2022, meaning these supplements are not recommended. Smokers and asbestos-exposed individuals have already suffered harm from their use. Antioxidants naturally present in fruits and vegetables are not covered by this recommendation, so they can still be consumed as normal.