Antioxidants are a group of vitamins and minerals that protect your body against free radicals (which cause oxidative damage to your cells). Diets rich in whole foods, particularly brightly-coloured fruits and vegetables (which are high in antioxidants) are protective against many diseases which are caused by oxidative damage.
Given the benefits of antioxidants, scientists decided to investigate antioxidant supplements. Let’s turn to research to see if antioxidant supplementation is worthwhile.
Currently, no research has found that antioxidant supplementation is able to decrease mortality (rate of death). Some research shows that some antioxidants can slightly increase mortality, for example, some studies have linked the use of high-dose beta-carotene supplements to an increased risk of lung cancer in smokers (Cortés-Jofré et al., 2012) and bladder cancer (Jeon et al., 2011) and the use of high-dose vitamin E supplements to increased risks of hemorrhagic stroke (a type of stroke caused by bleeding in the brain) (Schürks et al., 2011).
Your body naturally produces free radicals when you exercise, so providing antioxidant supplements was thought to improve exercise performance by combating these free radicals. However, several studies have found that taking antioxidant supplementation can interrupt your body’s natural adaptations to exercise and may even reduce the health benefits that exercise provides (Morrison et al., 2015)
Like some other supplements, antioxidant supplements may interact with certain medications. For example, vitamin E supplements may increase the risk of bleeding in people who are taking anticoagulant drugs (“blood thinners”). There is conflicting evidence on the effects of taking antioxidant supplements during cancer treatment; some studies suggest that this may be beneficial, but others suggest that it may be harmful. It is recommended that you speak to your doctor before starting any supplements.
Regular vitamin C has not been shown to prevent the common cold, but it may reduce its severity and duration.
In a large meta-analysis (an analysis that groups the data of several studies) of 29 studies with around 11,000 participants, taking vitamin C supplements (1-2 g daily) was shown to decrease the duration of colds by 8% while also decreasing their severity (Hemilä & Chalker, 2013). It is even more effective in people who are under intense physical stress- in marathon runners and skiers, vitamin C almost halved the duration of the common cold. It is recommended to take vitamin C in smaller doses — usually less than one gram — given that higher doses are less well-absorbed and can cause stomach upset (NRV, 2017).
Keep in mind that therapeutic supplementation, that is, taking vitamin C supplements once you get common cold symptoms, was not found to be effective. Rather vitamin C supplements would need to be taken on a regular basis to see any benefit. The authors concluded that considering the level of benefit is relatively small, long-term supplementation is not justified in its own right. However, “given the low cost and safety, it may be worthwhile for common cold patients to test on an individual basis whether therapeutic vitamin C is beneficial for them” (Hemilä & Chalker, 2013).
In short, there are several types of antioxidant supplements and most don’t provide any benefits, with some showing potential harm. On the other hand, while Vitamin C supplementation can’t prevent or treat colds it can modestly reduce the duration and severity of common colds if taken on a regular basis. Overall it is recommended to get your antioxidants from your diet, which you can do by eating plenty of antioxidant-rich whole foods e.g. vegetables and fruits, whole grains, nuts, seeds and legumes.
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Cortés-Jofré, M., Rueda, J. R., Corsini-Muñoz, G., Fonseca-Cortés, C., Caraballoso, M., & Bonfill Cosp, X. (2012). Drugs for preventing lung cancer in healthy people. The Cochrane database of systematic reviews, 10, CD002141. https://doi.org/10.1002/14651858.CD002141.pub2
Douglas, R. M., Chalker, E. B., & Treacy, B. (1998). Vitamin C for the common cold. Cochrane Database of Systematic Reviews(2). https://doi.org/10.1002/14651858.CD000980
Jeon, Y.-J., Myung, S.-K., Lee, E.-H., Kim, Y., Chang, Y. J., Ju, W., Cho, H.-J., Seo, H. G., & Huh, B. Y. (2011). Effects of Beta-Carotene Supplements on Cancer Prevention: Meta-Analysis of Randomized Controlled Trials. Nutrition and Cancer, 63(8), 1196-1207. https://doi.org/10.1080/01635581.2011.607541
Morrison, D., Hughes, J., Della Gatta, P. A., Mason, S., Lamon, S., Russell, A. P., & Wadley, G. D. (2015). Vitamin C and E supplementation prevents some of the cellular adaptations to endurance-training in humans. Free radical biology & medicine, 89, 852–862. https://doi.org/10.1016/j.freeradbiomed.2015.10.412
National Health and Medical Research Council (Australia) and Ministry of Health (New Zealand) (2017) Nutrient Reference Values for Australia and New Zealand: Nutrients.
Schürks, M., Glynn, R. J., Rist, P. M., Tzourio, C., & Kurth, T. (2010). Effects of vitamin E on stroke subtypes: meta-analysis of randomised controlled trials. BMJ (Clinical research ed.), 341, c5702. https://doi.org/10.1136/bmj.c5702
Last Reviewed: 20/06/22
Last modified: July 14, 2022
