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

Antioxidant supplements are not merely useless. Pooling 78 trials and nearly 300000 people, in the more rigorously designed trials those who took them had a slightly higher death rate. In two large trials done specifically on smokers, beta-carotene raised the share who got lung cancer by 18% to 28%. Deaths were also higher by 8% to 17%. Smokers and people exposed to asbestos especially should not take them.

Cost

Approximately 0.5 to 2 yuan per day. For smokers, the real cost is a higher risk of lung cancer.

Benefit

Cochrane reviewed 78 randomized controlled trials with 296,707 participants total. The overall risk ratio for mortality among supplement users was 1.02 (95% CI 0.98–1.05). When only higher-quality trials were considered, the risk ratio rose to 1.04 (1.01–1.07). Specifically, beta-carotene raised mortality risk to 1.05 (1.01–1.09) and vitamin E to 1.03 (1.00–1.05). The ATBC trial tracked 29,133 male smokers who took 20 mg daily; it found a 18% increase in lung cancer incidence (3%–36%) and an 8% rise in overall mortality (1%–16%). The CARET trial involved 18,314 smokers or asbestos-exposed individuals; it showed a 28% higher risk of lung cancer (RR 1.28, 1.04–1.57) and a 17% higher risk of all-cause mortality (RR 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 reasoning seems intuitive but is untrue.

Notes

The U.S. Preventive Services Task Force (USPSTF) rated both beta-carotene and vitamin E as “D” in 2022, meaning they advise against their use. Smokers and asbestos-exposed individuals have already suffered harm from taking them. Naturally occurring antioxidants found in fruits and vegetables are not included in this recommendation; you may continue eating those as normal.

Sources · 3

1. Bjelakovic G et al. (2012). Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev. doi.org/10.1002/14651858.CD007176.pub2
2. 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. doi.org/10.1056/NEJM199404143301501
3. Omenn GS et al. (1996). Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. NEJM. doi.org/10.1056/NEJM199605023341802