Answers to Antioxidant Questions
Susan M. Kleiner, PhD, RDTHE PHYSICIAN AND SPORTSMEDICINE - VOL 24 - NO. 8 - AUGUST 96
It seems like the more things change, the more they stay the same. For decades, dietitians told you to eat a balanced diet of a variety of foods and to eat in moderation. Then came news that antioxidants may help your body function better, prevent certain diseases, and relieve muscle damage and soreness after exercise. Dietitians wondered if eating whole foods was not enough and whether you should supplement your diet with antioxidants.
But currently, in light of new research (1), scientists are rethinking their recommendations about antioxidant supplements. So what's the final word? Even though the research gets confusing, learning more about antioxidants will help you make a decision.
What Is an Antioxidant?
Your body naturally produces chemicals called free radicals that cause irreversible damage (oxidation) to cells. They can leave your body vulnerable to advanced aging, cancer, cardiovascular disease, and degenerative diseases like arthritis.
Although your body has a natural antioxidant mechanism that protects you from most cell damage, certain environmental factors, like cigarette smoke, exhaust fumes, radiation, excessive sunlight, certain drugs, and stress, can increase free radicals. And, ironically, so can the healthy habit of exercising.
Fortunately, many substances in food act as antioxidants. Scientists have conducted studies, particularly on vitamins E and C, and the nutrient beta-carotene, to find out what role they play in protecting you.
Cardiovascular disease. One cause of heart disease is arterial plaque, which is the buildup of cholesterol (a fatty substance) on your artery walls. The main culprit of plaque buildup is thought to be the oxidation of low-density lipoprotein cholesterol (LDL-C).
Early studies (2,3) found that vitamin E decreases LDL-C oxidation. The greatest risk reduction occurred in men and women who took 100 mg of vitamin E per day (the recommended dietary allowance [RDA] is 12 mg for women and 15 mg for men). More recent research (4) found that the minimum dose of vitamin E needed to significantly decrease the risk is 400 mg per day.
But to confuse the issue, a study (5) on women who had gone through menopause refuted these findings. Women who ate moderate amounts of foods rich in vitamin E had about half the chance of dying from heart disease than women who avoided vitamin E-rich foods. But there was no decrease in risk for women who took vitamin E supplements.
Cancer. Because research (6) found that people who ate foods rich in vitamin C and beta-carotene lowered their risk of developing many cancers, scientists began to study whether supplements could help even more.
It may be too soon to tell. Many studies look promising, but two (7,8) completed within a year of each other showed such startling preliminary results that the researchers stopped the studies early. In both studies, smokers supplemented with beta-carotene had a greater risk of developing lung cancer than those who were not supplemented. And another study (9) found no evidence that supplementing with 50 mg of beta-carotene lowered death rates from cancer, heart disease, or any other causes.
The Exercise Equation
During exercise, your body naturally produces more free radicals. Certain exercises, such as weight lifting or running downhill, can lead to muscle injury and soreness and the production of even more free radicals that can last for many days.
By far the most promising studies about antioxidants and exercise have centered around vitamin E. These studies (10,11) have shown that vitamin E reduces free radical production and oxidation related to exercise. In one of the studies (10), subjects over age 55 who ran and walked downhill benefited from a daily 800-mg vitamin E supplement. Subjects under age 30, however, did not benefit. The author concluded that as people age, their vitamin E levels decrease--but their need for them increases--and that supplements can help.
Back to Basics?
It seems clear that people who consume diets high in antioxidant-containing foods are protected from many chronic diseases. Even though research appears to be contradictory, it may be that the evidence has been somewhat misinterpreted. Perhaps the protection you get from food comes from the food itself and the combination of its compounds, rather than just the specific antioxidant it contains.
The amounts of vitamin C and beta-carotene that seem to be protective are easily obtained from food. To get enough of these two vitamins, follow the United States Department of Agriculture's Food Guide Pyramid recommendations (12). Strive to eat 3 to 5 servings of vegetables and 2 to 4 servings of fruits every day (table 1: not shown).
Getting enough vitamin E in your diet may be tricky because the greatest sources of vitamin E are foods rich in vegetable oils, like seeds, nuts, and wheat germ. Like many active people, you may be lowering your fat intake and not meeting the RDA for vitamin E. Try adding some vitamin E sources into your diet and don't be afraid of a little fat: A diet low in fat does not mean a diet devoid of fat.
If you still aren't getting enough vitamin E, a supplement of 100 to 400 mg per day is adequate. If you'd like to boost your intake of the other antioxidants as well, take a one-a-day vitamin-mineral supplement that contains antioxidants. Reasonable levels are 250 mg of vitamin C and 5 to 6 mg of beta-carotene.
When the research gets confusing, consider the entire body of evidence, and look for long-term trends. The evidence weighs heavily on the side of eating exactly as we've always been told: with balance, variety, and moderation.
- Omenn GS, Goodman GE, Thornquist MD, et al: Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med 1996;334(18):1150-1155
- Stampfer MJ, Hennekens CH, Manson JE, et al: Vitamin E consumption and the risk of coronary disease in women. N Engl J Med 1993;328(20): 1444-1449
- Rimm EB, Stampfer MJ, Ascherio A, et al: Vitamin E consumption and the risk of coronary heart disease in men. N Engl J Med 1993;328(20):1450-1466
- Jialal I, Fuller CJ, Huet BA: The effect of alpha-tocopherol supplementation on LDL oxidation: a dose-response study. Arterioscler Thromb Vasc Biol 1995;15:190-198
- Kushi LH, Folsom AR, Prineas RJ, et al: Dietary antioxidant vitamins and death from coronary heart disease in postmenopausal women. N Engl J Med 1996;334(18):1156-1162
- Report of the Council on Scientific Affairs. Diet and cancer: where do matters stand? Arch Intern Med 1993; 153(1):50-56
- The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group: The effect of vitamin E and beta-carotene on the incidence of lung cancer and other cancers in male smokers. N Engl J Med 1994;330(15):1029-1035
- Omenn GS, Goodman G, Thornquist M: The beta carotene and retinal efficacy trial (CARET) for chemoprevention of lung cancer in high risk populations: smokers and asbestos-exposed workers. Cancer Research 1994;54(7 Suppl):2038-2042
- Hennekens CH, Buring JE, Manson JE: Lack of effect of long-term supplementation with beta carotene on the incidence of malignant neoplasms and cardiovascular disease. N Engl J Med 1996;334(18):1145-1149
- Evans W: The protective role of antioxidants in exercise induced oxidative stress. Keynote address, 13th Annual SCAN Symposium, April 28, 1996, Scottsdale, Arizona
- Ji LL: Oxidative stress during exercise: implication of antioxidant nutrients. Free Radical Bio Med 1995;18(6):1079-1086
- The Food Guide Pyramid. United States Department of Agriculture Human Nutrition Information Service. Home and Garden Bulletin Number 252, August, 1992
Remember: You, your physician, and your nutritionist need to work together to discuss nutrition concerns. The above information is not intended as a substitute for appropriate medical treatment.
Dr Kleiner is a private nutrition consultant to athletes in the Seattle area. She is a member of the American College of Sports Medicine and of the American Dietetic Association and its practice group, Sports and Cardiovascular Nutritionists (SCAN), and a fellow of the American College of Nutrition.