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Facts about Antioxidants1

Kaitlin G. Clark and Wendy J. Dahl2

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 (Jenkins and Honig 1996). 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 found in vegetables containing them. Vitamin C and vitamin E also function as antioxidants. Table 1 shows some common food sources of antioxidants.

Table 1. 

Some common food sources of antioxidants1.

Food Source

Antioxidant Content

Food Source

Antioxidant Content

 

Vitamin C1

mg

 

Lutein +

Zeaxanthin1

mg

red peppers (1 medium)

152

spinach (1/2 cup cooked)

15

green pepper (1 medium)

96

kale (1/2 cup cooked)

13

broccoli (1 cup chopped)

81

collards (1/2 cup cooked)

9

orange (1 medium)

68

peas (1/2 cup cooked)

2

kiwifruit (1)

64

squash (1/2 cup cooked)

2

grapefruit (1 medium)

38

broccoli (1/2 cup cooked)

1

 

Vitamin E1

mg

 

Lycopene1

mg

wheat germ (1 oz.)

4.5

tomato juice (1 cup)

22

almonds (1 oz.)

7.3

watermelon (1 wedge)

13

safflower oil (1 Tbsp.)

4.6

ketchup (1 Tbsp.)

2.5

hazelnuts (1 oz.)

4.3

pink grapefruit (1/2)

2

 

Vitamin A1 RAE* micrograms

 

Beta-carotene1

micrograms

sweet potato (1/2 cup canned)

955

pumpkin pie (1 slice)

7366

pumpkin (1/2 cup canned)

953

spinach (1/2 cup cooked)

5659

carrots (1/2 cup cooked)

665

sweet potato (1 small baked)

6905

cantaloupe (1 small)

745

carrot (1 medium)

5054

spinach (1/2 cup cooked)

472

collards (1/2 cup cooked)

4287

1 (USDA, 2013)

*RAE = Retinol Activity Equivalents; 1 RAE = 1 microgram retinol; 1 microgram retinol = 12 micrograms beta-carotene, thus values for vitamin A include beta-carotene.

Antioxidant Activity

There are many other antioxidants that help protect the body. The amount of other 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).

Recommended Intake

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).

Table 2. 

RDA for vitamins C, E, and A

Age (years)

Vitamin C (mg/day)

Vitamin E

(mg/day)

(as α-tocopherol)

Vitamin A

(micrograms/day)

(RAE*)

Children 1–3 years

15

6

300

Children 4–8 years

25

7

400

Males 9–13 years

45

11

600

Males 14–18

75

15

900

Males >19

90

15

900

Females 9–13

45

11

600

Females 14–18

65

15

700

Females >19

75

15

700

*Retinol Activity Equivalents

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.

Antioxidant Supplements

While consuming antioxidants from fruits and vegetables is associated with a decreased risk of cancer and cardiovascular disease (Garrido, Terron, & Rodriguez 2013), taking antioxidants as supplements is not recommended due to increased risk (Bjelakovic et al. 2012).

References

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. Retrieved from http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD007176.pub2/abstract;jsessionid=EC594E97108DBA5C8DF87E62312EB6FB.f01t01

Garrido, M., Terron, M.P., Rodriguez, A.B. (2013). Chrononutrition against oxidative stress in aging. Oxidative Medicine and Cellular Longevity. Retrieved from http://www.hindawi.com/journals/oximed/2013/729804/

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.

Jenkins, M., Honig, C. (1996). Antioxidants and free radicals. Retrieved from http://www.rice.edu/~jenky/sports/antiox.html

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. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249911/

Mandelker, L. (2008). Cellular effects of common antioxidants. The Veterinary Clinics of North America. Small Animal Practice, 38(1), 199-211. Retrieved from http://www.sciencedirect.com/science/article/pii/S0195561607001362

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. Retrieved from http://pubs.acs.org/doi/abs/10.1021/jf9035832

U.S. Department of Agriculture, National Academy of Sciences. Institute of Medicine. Food and Nutrition Board. (n.d.). Dietary Reference IKntakes: Recommended Dietary Allowances and Adequate Intakes, Vitamins. Retrieved from http://iom.edu/Activities/Nutrition/SummaryDRIs/~/media/Files/Activity Files/Nutrition/DRIs/RDA and AIs_Vitamin and Elements.pdf

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. Retrieved from http://pubs.acs.org/doi/abs/10.1021/jf801381y

U.S. Department of Agriculture, Agricultural Research Service. USDA Nutrient Database for Standard Reference, Release 26. 2013. Available at: http://www.nal.usda.gov/fnic/foodcomp/search/. Accessed December 29, 2013.

Footnotes

1.

This document is FSHN14-02, one of a series of the Food Science and Human Nutrition Department, UF/IFAS Extension. Original publication date February 2014. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Kaitlin G. Clark, MS-DI student; Wendy J. Dahl PhD, assistant professor; Department of Food Science and Human Nutrition, UF/IFAS Extension, Gainesville, FL 32611.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.