Q: Every time I walk into a health food store or open a fitness magazine, I see advertisements for antioxidants. These ads claim that I need to ingest antioxidant supplements if I exercise to counter the damaging effects of "free oxygen radicals." Is this true?
A: No, these ads are misleading. Let me explain why.
Each cell of the body must have oxygen to produce energy. As we take in oxygen during rest and exercise, some of the oxygen particles change and react with cell membranes and proteins, causing damage. These reactive oxygen particles are highly unstable and are known as free oxygen radicals. As the decades roll by, the oxidative damage caused by free oxygen radicals promotes cancer, heart disease, diabetes, and Alzheimer disease and accelerates aging, especially in people who are obese, smoke, and avoid fruits and vegetables in their diets (1, 2).
During intense exercise, oxygen intake by the body can increase 10- to 20-fold compared to rest. This increase in oxygen consumption causes an "oxidative stress" that leads to higher than normal production of free oxygen radicals (3). Although companies that sell antioxidant supplements like to emphasize this fact, what they leave out is that the body is equipped with a sophisticated defense system that is quite efficient in eliminating most of the radicals. This defense system consists of antioxidant enzymes that battle radicals on the front lines, with antioxidant nutrients from the diet providing the second line of defense (3).
Most studies show that the antioxidant defense system improves with your level of fitness (3, 4). In other words, the more you exercise, the more your body turns into a strong fortress against the onslaught of free radicals. A good analogy is the link between weight training and muscle size. At first, you feel muscle soreness, but over time, weight training produces bigger and stronger muscles. In much the same way, aerobic exercise produces oxidative stress but then, as the weeks go by, stimulates improved antioxidant defenses. In fact, exercise training is so effective as an antioxidant therapy that it helps counter the negative effects of oxidative stress on aging and heart disease (4, 5).
But let me emphasize that the antioxidants from your diet also play a critical role in protecting cells in your body from these reactive oxygen particles. There are many types of antioxidants found in certain types of nutrients and chemicals from the diet (Table). Vitamins E and C and the vitamin A precursor, β-carotene, are strong antioxidants and are found in fruits, vegetables, whole grains, and nuts and seeds. Good sources of vitamin E are vegetable oils, nuts and seeds, the wheat germ in whole-grain products, and dark green vegetables. Vitamin C is found in most fruits and vegetables. β-Carotene is found in orange fruits and vegetables (e.g., carrots, apricots, cantaloupe, squash, and sweet potatoes) and dark green vegetables (e.g., spinach, kale, and broccoli).
Phytochemicals such as lutein and lycopene (Table) are special chemicals within plants that are not vitamins or minerals but have health-protective effects (6). Some phytochemicals have antioxidant activity, although they work in many other ways, too. Nuts, seeds, whole grains, fruits, and vegetables contain an abundance of phytochemicals that help prevent chronic disease, including cancer. The foods and herbs with the highest anticancer activity include garlic, soybeans, cabbage, ginger, carrots, celery, cilantro, parsley, and parsnips. Other foods with cancer-protective activity include onions, citrus fruits, broccoli, brussel sprouts, cabbage, cauliflower, tomatoes, pepper, brown rice, and whole wheat. In general, phytochemicals are most abundant within the red, yellow, orange, green, and purple colors of fruits and vegetables.
Do antioxidant supplements boost defenses against free oxygen radicals? In other words, if a certain amount from your diet is good, is 100 times that amount from using a supplement better? The answer is "no," with several recent studies showing that large antioxidant supplements harm health more than they help (7).
And for athletes, the latest research also indicates "no." In my laboratory, we have given elite athletes huge amounts of vitamin C (1,500 mg/day) and vitamin E (800 IU/day) and then compared oxidative stress and immune suppression with athletes using placebos before and after competing in Ironman triathlons and 50- to 100-mile race events (8, 9). Not only did the antioxidant supplements fail to counter oxidative stress in these athletes, they also were ineffective in protecting their immune systems.
In general, the best strategy to promote health and fitness is to be physically active and consume five or more servings of fruits and vegetables each day, and six or more servings of whole grains. Count on your exercise program to build your antioxidant defense system. Antioxidant supplements beyond a healthy diet are not needed. Fruits and vegetables are complex foods containing more than 100 beneficial vitamins, minerals, fiber, and other substances, and no pill has captured their protective effects. One of the strongest findings from science in the past decade is that the fittest and healthiest people on earth are physically active and have diets emphasizing colorful fruits and vegetables, and whole grains (7).
1. Cutler, R.G., J. Plummer, K. Chowdhury, et al. Oxidative stress profiling: Part II. Theory, technology, and practice. Annals of the New York Academy of Sciences
2. Vincent, H.K., and A.G. Taylor. Biomarkers and potential mechanisms of obesity-induced oxidant stress in humans. International Journal of Obesity (London)
3. Powers, S.K., K.C. DeRuisseau, J. Quindry, et al. Dietary antioxidants and exercise. Journal of Sports Sciences
4. Kojda, G., and R. Hambrecht. Molecular mechanisms of vascular adaptations to exercise. Physical activity as an effective antioxidant therapy? Cardiovascular Research
5. Yu, B.P., and H.Y. Chung. Adaptive mechanisms to oxidative stress during aging. Mechanisms of Ageing and Development
6. Ji, L.L., and D.M. Peterson. Aging, exercise, and phytochemicals: promises and pitfalls. Annals of the New York Academy of Sciences
7. Kris-Etherton, P.M., A.H. Lichtenstein, B.V. Howard, et al, and the Nutrition Committee of the American Heart Association Council on Nutrition, Physical Activity, and Metabolism. Antioxidant vitamin supplements and cardiovascular disease. Circulation
8. Nieman, D.C., D.A. Henson, S.R. McAnulty, et al. Vitamin E and immunity after the Kona Triathlon World Championship. Medicine and Science in Sports and Exercise
9. Nieman, D.C., D.A Henson, S.R. McAnulty, et al. Influence of vitamin C supplementation on oxidative and immune changes following an ultramarathon. Journal of Applied Physiology