Our bodies are made up of cells. Chemical reactions, known collectively as metabolism, are constantly occurring inside our cells. These reactions are necessary for life, but sometimes they create free radicals. Free radicals are highly reactive molecules that can initiate damaging chain reactions in our cells (Alkadi 2020). This is known as oxidative stress. Research has linked oxidative stress to many diseases: arthritis, lung diseases (such as emphysema), heart disease, stroke, ulcers, hypertension, Parkinson’s and Alzheimer’s diseases, muscular dystrophy, and others. Oxidative stress also contributes to the normal aging process (Lobo et al. 2010).
Antioxidants can inactivate free radicals and protect our cells from oxidative stress and the damage it causes. Antioxidants also can help our immune system defend against bacteria, fungi, viruses, and some cancers (Mandelker 2008). The body produces some of its own antioxidants but eating a plant-based diet increases the level of antioxidants in our bodies.
Sources of Antioxidants
There are many different compounds that can act as antioxidants. Some, such as carotenoids (e.g., beta-carotene, lutein, lycopene), can be identified by the orange-red color of the vegetables containing them. Vitamin C and vitamin E also function as antioxidants. Table 1 shows some common food sources of antioxidants.
The amounts of antioxidants in a food can be determined as "antioxidant activity," which is a measure of how well they inhibit free radicals. The fruits highest in antioxidant activity are blueberries, pomegranates, blackberries, strawberries, and raspberries (Wolfe et al. 2008). The vegetables highest in antioxidant activity are beets, red peppers, eggplant, Brussels sprout, and broccoli (Song et al. 2010).
The Recommended Dietary Allowances (RDA) for antioxidant vitamins are given in Table 2. Because smokers have higher levels of oxidative stress, an additional 35 mg per day of vitamin C is recommended (IOM 2001).
RDA for vitamins C, E, and A
Other antioxidants are not vitamins and do not have recommended intakes. Plant foods are the best source of antioxidants. Making half of your daily food intake fruits and vegetables (especially dark-green, red, and orange vegetables) and choosing whole grains should provide plenty of antioxidants in your diet. It is also important to consume a variety of fruits and vegetables, since different antioxidants are found in different foods.
While consuming antioxidants from fruits and vegetables is associated with a decreased risk of cancer and cardiovascular disease (Garrido, Terron, and Rodriguez 2013), taking antioxidants as supplements is not recommended due to increased risk of disease (Bjelakovic et al. 2012).
Alkadi, H. 2020. “A Review on Free Radicals and Antioxidants.” Infectious Disorders-Drug Targets (Formerly Current Drug Targets-Infectious Disorders) 20(1):16-26..
Bjelakovic, G., Nikolova, D., Gluud, L.L., Simonetti, R.G., Gluud, C. 2012. "Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases." Cochrane Database of Systematic Reviews 3 (2020). https://doi.org/10.1002/14651858.CD007176.pub2.
Institute of Medicine. 2001. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academies of Science. Washington, D.C.
Lobo, V., Patil, A., Phatak, A., & Chandra, N. 2010. "Free radicals, antioxidants and functional foods: Impact on human health." Pharmacognosy Review, 4(8), 118-126.
Mandelker, L. 2008. "Cellular effects of common antioxidants." The Veterinary Clinics of North America. Small Animal Practice, 38(1), 199-211..
Song, W., Derito, C. M., Liu, M.K., He, X., Dong, M., & Liu, R.H. 2010. "Cellular antioxidant activity of common vegetables." Journal of Agricultural and Food Chemistry, 58(11), 6621-6629. https://doi.org/10.1021/jf9035832.
U.S. Department of Agriculture, National Academy of Sciences. Institute of Medicine. Food and Nutrition Board. n.d. "Dietary Reference Intakes: Recommended Dietary Allowances and Adequate Intakes, Vitamins." Accessed March 16, 2021. https://ods.od.nih.gov/HealthInformation/Dietary_Reference_Intakes.aspx.
U.S. Department of Agriculture, Agricultural Research Service. n.d. "FoodData Central." Accessed February 18, 2022. https://fdc.nal.usda.gov/.
Wolfe, K. L., Kang, X., He, X., Dong, M., Zhang, Q., & Liu, R. H. 2008. "Cellular antioxidant activity of common fruits." Journal of Agricultural and Food Chemistry, 56(18), 8418-8426. Accessed March 16, 2021. https://doi.org/10.1021/jf801381y.
Some common food sources of antioxidants.1