As the body uses oxygen, free radicals—oxygen molecules that are missing electrons—are formed. These free radicals are unstable molecules that can cause damage to cells. This cell damage is thought to build up over time and may lead to aging and disease. Everything from cancer and heart disease, to wrinkles and cataracts may be attributed to the action of free radicals. Environmental factors, such as exposure to radiation and tobacco smoke may also increase the number of free radicals in the body.
Antioxidants are compounds that work to deactivate free radicals. The best known antioxidants are vitamins A, E, C and beta-carotene, but there are many others, including selenium, lutein, and lycopene.
The ability of antioxidant supplements to prevent disease has not been widely supported by scientific evidence. Some observational studies (which track participants without making changes to their diet or treatments) have found reduced risk of certain diseases with a higher intake of fruits and vegetables that contain antioxidants. However, clinical trials have not shown any benefit.
One exception is the National Eye Institute study of age-related eye disease. It found that a combination of antioxidants and zinc reduced age-related macular degeneration (AMD) by 25% in people who had intermediate or advanced AMD in one eye. The risk was reduced by about 17% when antioxidants were used alone. Other studies demonstrated slowing of disease progression in patients with AMD or cataracts.
Some studies have suggested that for certain people, over consumption of antioxidants can be harmful. Studies of beta-carotene in humans were stopped in 1994, after results suggested that people at risk for cancer were at even greater risk after taking high doses of synthetic beta-carotene. Taking more than 400 units a day for more than a year increases your risk of death from any cause.
Though the jury is still out on the role of antioxidant supplements as disease and age fighters, consuming more antioxidant-rich fruits and vegetables has well-documented benefits in improving health, aside from their antioxidant contents.
|Antioxidant||Recommended Amount*||Good Food Sources|
Women: 75 mg
Men: 90 mg
Smokers: extra 35 mg
|Citrus fruits; vegetables such as broccoli, cauliflower, and kale|
|Vitamin E||15 mg||Fortified cereals, vegetable oils, nuts, mangoes, and wheat germ|
|Selenium||55 micrograms (mcg)||Tuna, ham, brown rice, whole wheat bread|
Women: 700 REA**
Men: 900 REA
Eggs, liver, vitamin A-fortified milk
Yellow-orange or dark-green leafy vegetables and fruits, such as kale, beet greens, spinach, carrots, sweet potatoes, pumpkin, papaya, apricots, parsley, and basil
*Recommended amounts are given as dietary reference intakes (DRIs), which replace recommended dietary allowances (RDAs); these are the government's recommendations for good health.
**REA = retinol equivalents; a measurement of vitamin A that includes the two major forms of vitamin A found in foods: retinol and beta-carotene. There is no separate DRI set for beta-carotene.
The American Heart Association and the American Cancer Society do not endorse antioxidant supplements for the general population, but they do recommend a diet with plenty of antioxidant-rich fresh fruits, vegetables, and whole grains. You should also discuss any antioxidant use with your doctor before you begin.
American Heart Association
National Institute on Aging
Canadian Cancer Society
Canadian Cardiovascular Society
Antioxidant. EBSCO Natural and Alternative Treatments website. Available at: http://www.ebscohost.com/biomedical-libraries/natural-alternative-treatments. Updated August 22, 2013. Accessed July 2, 2014.
Antioxidant Supplements for Health: An Introduction. National Center for Complementary and Alternative Medicine website. Available at: http://nccam.nih.gov/health/antioxidants. Updated March 3, 2013. Accessed July 2, 2014.
The heart outcomes prevention evaluation study investigators, vitamin E supplementation and cardiovascular events in high-risk women. N Engl J Med. 2000;342:154-160.
Kris-Etherton PM, Lichtenstein AH. Antioxidant vitamin supplements and cardiovascular disease. Circulation. 2004;110(5):637-641.
Meydani M. Nutrition interventions in aging and age-associated disease. Ann N Y Acad Sci. 2001;928:226-235.
Phytochemicals. American Cancer Society website. Available at: http://www.cancer.org/treatment/treatmentsandsideeffects/complementaryandalternativemedicine/herbsvitaminsandminerals/phytochemicals. Updated January 17, 2013. Accessed July 2, 2014.
Selenium. EBSCO Natural and Alternative Treatments website. Available at: http://www.ebscohost.com/biomedical-libraries/natural-alternative-treatments. Updated August 22, 2013. Accessed July 2, 2014.
Vitamin A. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated January 6, 2014. Accessed July 2, 2014.
Vitamin C. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated December 3, 2013. Accessed July 2, 2014.
Vitamin E. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated March 6, 2013. Accessed July 2, 2014.
Last reviewed July 2014 by Michael Woods, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.