Antioxidants are a broad group of compounds that destroy single oxygen molecules, also called free radicals, in the body, thereby protecting against oxidative damage to cells. They are essential to good health and are found naturally in a wide variety of foods and plants, including many fruits and vegetables. Many antioxidants, either singly or in combination, are also available as over-the-counter nutritional supplements in tablet or capsule form. The most commonly used antioxidants are vitamin C, vitamin E, and beta carotene. Others include grape seed extract, vitamin A, selenium, and coenzyme Q10. It is unknown whether or not supplemental antioxidants provide the same benefits as those occurring naturally in foods, however.
In brief, antioxidants destroy free radicals in the body. Free radicals are byproducts of oxygen metabolism that can damage cells and are among the causes of many degenerative diseases, especially diseases associated with aging. They are also associated with the aging process itself. As a person ages, cell damage accumulates, and supplementing the diet with extra antioxidant-rich foods can help slow the oxidative damage done to cells. Scientific studies validate the role of antioxidants in preventing many diseases. Although studies have shown lower rates of cancer and heart disease in people who eat a recommended amount of fruits and vegetables, recent clinical studies have shown that supplementation
Many herbs and medicinal plants are good natural sources of antioxidants. These include carrots, tomatoes, yams, leafy greens, blueberries, billberries, ginkgo biloba, garlic, and green tea, to name a few. A diet rich in vitamin C, vitamin E, and beta carotene may help reduce the risk of some cancers, heart disease, cataracts, and strokes.
A study by the University of Arizona found that vitamin A has a protective affect against many types of cancer, according to Dr. Michael Colgan in his book, The New Nutrition. Vitamin A is a fat-soluble antioxidant found in animal products but can be made by the body from its precursor, beta carotene. Foods rich in vitamin A are liver, eggs, and fortified dairy products. Vitamin A helps bones and teeth develop, and promotes vision. As an antioxidant, it protects cell membranes and fatty tissue, helps repair damage caused by air pollutants, and boosts the immune system. A deficiency of this vitamin can result in dry skin, brittle hair, vision problems, blindness, and increased susceptibility to respiratory infections.
Probably the most widely used of all vitamin supplements, vitamin C is a powerful antioxidant that has a myriad of functions and helps strengthen the immune system. It became famous in the 1970s when Nobel Prize-winning scientist Linus Pauling advocated daily mega doses (8-10 grams) of vitamin C to prevent and ease the symptoms of the common cold. Many clinical studies that show vitamin C is superior to over-the-counter medicines in reducing the symptoms, duration, and severity of colds. As an antioxidant, vitamin C may help fight cardiovascular disease by protecting the linings of arteries from oxidative damage. In 2002, debate still continued on the vitamin's effects on heart disease. One study revealed that Vitamins C and E helped reduce arteriosclerosis (hardening of the arteries) following heart transplants. Yet another study demonstrated that vitamin therapy had not effect on preventing heart disease. There is some evidence and research that vitamin C can help prevent cancer. Studies have shown it is also beneficial in protecting the body against the effects of smoking and air pollutants.
Vitamin E is a potent antioxidant by itself, but its effectiveness is magnified when taken with other antioxidants, especially vitamin C, selenium, and beta carotene. Some scientific evidence indicates that vitamin E helps promote cardiovascular health. Past studies have demonstrated higher vitamin E intake is associated with decreased incidence of heart disease in both men and women. In fact, the combination of Vitamin C and E can slow progression of cardiovascular disease following heart transplant. In 2002, researchers stated that the vitamin combination might also be useful in other organ transplants. In addition, Harvard Medical School reported in the same year that Vitamin E might play a role in helping people live longer, citing its role in strengthening the immune system.
This class of antioxidants includes beta carotene, lutein, and lycopene. They are found in a variety of fruits and vegetables such as carrots, pumpkins, kale, spinach, tomatoes, and pink grapefruit. Research evidence suggests carotenoids lower the risk of heart disease and some types of cancer, and strengthen the immune system. Lycopene, which is concentrated in the prostate gland, is believed to protect the prostate from cancer. Lutein is thought to prevent macular degeneration, a major cause of blindness, or stop its progression. Beta carotene increases the lungs' defense system in smokers or those exposed to other air-borne pollutants. It also has been used as an immune system stimulator in people with AIDS. In 2002, a report revealed that more than 90% of ophthalmologists and optometrists surveyed believe that lutein helps prevent eye disease.
Bioflavonoids are a group of about 5,000 compounds that act as antioxidants. They occur in fruits, vegetables, green tea, soy products, herbs, and spices. A combination of bioflavonoids has a synergistic effect when taken with vitamin C. They have been shown to be beneficial in treating a variety of conditions, including allergies, arthritis, diabetes, hypertension, and viral infections. One group of bioflavonoids found to be a powerful antioxidant is oligomeric proanthocyanidins (OPCs), also known generically as pycnogenol. Extremely high concentrations of OPCs are found in maritime pine bark (Pinus maritima) extract, grape seed extract, and grape and peanut skins. Due primarily to its much lower cost, grape seed extract is the most commonly used OPC. Procyanidins, a group of compounds found in the extract, are thought to increase the effectiveness of other antioxidants, especially vitamin C and vitamin E, by helping them regenerate after neutralizing free radicals in the blood and tissue.
The other widely used antioxidants are selenium, coenzyme Q10, and certain amino acids. Selenium, especially
Bottled antioxidant formulae are available in a single pill or as part of a multivitamin. The usual dosages of antioxidants taken individually can vary widely. The United States Department of Agriculture (USDA) has established recommended daily allowance, but these may be conservative amounts for preventing diseases. For instance, the USDA recommendation for vitamin C is 60 mg a day but natural healthcare practitioners commonly recommend 500 mg a day or more. The dosage may also depend on whether it is being taken to treat or prevent a specific condition. With that in mind, the common daily dosages for specific antioxidants are: vitamin A, 5,000-15,000 IU; beta carotene, 15,000-25,000 IU; vitamin C, 250-1,500 mg; vitamin E, 30-400 IU; selenium, 50-400 micrograms; bioflavonoids, 100-500 mg; grape seed extract, 150-200 mg; coenzyme Q10, 90-150 mg; alpha lipoic acid, 20-50 mg or 300-600 mg for elevated blood sugar levels; glutathione, 100 mg; N-acetyl cysteine, 600 mg.
Vitamin C: May interfere with some laboratory tests, including urinary sugar spilling for diabetics. Vitamin A: Can be toxic in high doses of more than 15,000 IU per day or chronic doses for months, and may cause birth defects if taken in high doses during pregnancy. In 2002, one study showed that consistent Vitamin A intake could increase the risk of hip fractures in postmenopausal women, but the study was not representative of all women, and more study on the upper limits of safe Vitamin A consumption for women in their 40s and 50s is needed. Vitamin E: Dangerous in very high doses. Carotenoids: No known precautions are indicated for normal doses. Bioflavonoids: No known precautions are indicated for normal doses. Selenium: No precautions indicated at normal doses, but a physician should be consulted before taking daily doses of more than 200 micrograms. Coenzyme Q10: No known precautions are indicated for normal dosage. Amino acids: There are no known precautions indicated for alpha lipoic acid, cysteine, glutathione, or NAC.
Vitamin C: Individual tolerances vary. High doses may cause cramps, diarrhea, ulcer flare-ups, kidney stones, and gout in some people. Vitamin A: High doses can lead to headaches, nausea, hair loss, and skin lesions; may cause bone disease in people with chronic kidney failure. Vitamin E: Usually no adverse side effects in doses of up to 400 mg a day, high doses may elevate blood pressure and lead to blood-clotting problems. Carotenoids: No known side effects occur with normal dosage. Bioflavonoids: No known negative side effects in normal doses. Selenium: No reported adverse side effects with normal dosage of 200 micrograms, higher doses may cause dizziness and nausea. Coenzyme Q10: No adverse side effects have been reported. Amino acids: There are no known side effects associated with normal doses of alpha lipoic acid, cysteine, glutathione, or NAC.
Vitamin C: No known common adverse interactions with other drugs. Vitamin A: Women taking birth control pills should consult with their doctors before taking extra vitamin A. Vitamin E: Should not be used by persons taking anti-coagulation drugs. Carotenoids: No known negative interactions with other drugs. Bioflavonoids: No known adverse interactions with other drugs. Coenzyme Q10: No negative drug interactions yet reported. Amino acids: There are no adverse reactions yet reported between alpha lipoic acid, cysteine, glutathione, or NAC and other medications.
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Ken R. Wells
Teresa G. Odle