Antioxidants

Description

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 Q ₁₀. It is unknown whether or not supplemental antioxidants provide the same benefits as those occurring naturally in foods, however.

General use

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 of diet with antioxidant vitamin therapy does not lower risk of cardiovascular disease or certain other diseases.

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.

Vitamin A

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 .

Vitamin C

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

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.

Carotenoids

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

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.

Other antioxidants

The other widely used antioxidants are selenium, coenzyme Q₁₀, and certain amino acids . Selenium, especially when teamed with vitamin E, may help protect against lung, colon, prostate, and rectum cancers. The antioxidant benefits of coenzyme Q₁₀ may include slowing the aging process, boosting the immune system, and preventing oxidative damage to the brain. Some still suggest its use to treat a variety of cardiovascular diseases. Amino acids that have strong antioxidant effects include alpha lipoic acid, cysteine, glutathione , and N-acetyl cysteine (NAC).

Preparations

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.

Precautions

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.

Side effects

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.

Interactions

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.

Resources

BOOKS

Balch, Dr. James F. The Super Antioxidants: Why They Will Change the Face of Health Care in the 21st Century. M. Evans and Co., 1998.

Colgan, Dr. Michael. The New Nutrition. CI Publications, 1996.

Challem, Jack, editor. All About Antioxidants. Avery Publishing Group, 1999.

Hendler, Dr. Sheldon Saul The Doctors'Vitamin and Mineral Encyclopedia. Simon and Shuster, 1990.

Moss, Ralph W. Antioxidants Against Cancer. Equinox Press, 2000.

Murray, Michael T. Natural Alternatives to Over-the-Counter and Prescription Drugs. William Morrow and Co., 1994.

Packer, Lester, et al. The Antioxidant Miracle: Your Complete Plan For Total Health and Healing. John Wiley and Sons, 1999.

Smythies, John R. Every Person's Guide to Antioxidants Rutgers University Press, 1998.

PERIODICALS

Abramowiez, Dr. Mark, editor. "Vitamin Supplements." The Medical Letter (July 31, 1998): 75-77.

"Antioxidant Vitamin E Reported to Strengthen Immune System." Obesity, Fitness & Wellness Week (March 2, 2002): 12.

Fang, James C., et al. "Effect of Vitamins C and E on Progression of Transplant-Associated Arteriosclerosis: A randomized Trial." The Lancet (March 30, 2002): 1108.

Kiningham, Robert."The Value of Antioxidant Vitamin Supplements." American Family Physician (Sept. 1, 1999): 742.

Koch Kubetin, Sally. "Antioxidants Fall Short." OB GYN News (February 1, 2002): 29.

Langer, Stephen."Antioxidants: Our Knights in Shining Armor." Better Nutrition (May 1997): 46-50.

"Lutein Helps Protect Eyes, Doctors Say in Survey." Ophthalmology Times (March 15, 2002): 29.

Raloff, Janet."The Heart-Healthy Side of Lycopene." Science News (Nov. 29, 1997): 348.

Scheer, James F. "Twelve Key Antioxidants: May Their Force Be With You." Better Nutrition (Jan. 1999): 58.

Schindler, Martha."The Magnificent Seven." Vegetarian Times (Feb. 1999): 86.

"Simvastatin Yes, Antioxidant No ñ Two Important New Studies." Clinical Cardiology Alert (January 2002): 1.

Tyler, Varro E."The Miracle of Anti-Aging Herbs." Prevention (Nov. 1999): 105.

"Vitamin A Intake Levels Reaffirmed as Safe and Beneficial." Medical Letter on the CDC & FDA (January 27, 2002): 14.

Ken R. Wells

Teresa G. Odle

Antioxidants

Americans spend several billion dollars a year on antioxidants in an effort to improve their health. Science has been looking at antioxidants and their role in everything from preventing cancer and heart disease to boosting the immune system and slowing the aging process. Antioxidants provide a layer of protection for the cells and tissues of the body, just as a thick coat of wax helps protect a car's finish. Specifically, antioxidants protect against free radical damage. What are free radicals ?

People must breathe in oxygen to live. Continuously on the move in the blood stream and transported to every cell, oxygen is necessary for all essential bodily functions. However, a small amount of this oxygen gets loose and produces unstable by-products called free radicals. Body processes, such as metabolism , as well as environmental factors, including pollution and cigarette smoke, can produce free radicals. An overload of free radicals in the body causes damage to the cells, ultimately resulting in disease and accelerated aging.

Antioxidant-rich food may help prevent various cancers, heart disease, and diseases of aging. Vitamins C and E, carotenoids (including beta-carotene), and the mineral selenium are all powerful antioxidants found in food. Vitamin C, a water-soluble vitamin, is also known as ascorbic acid. Most of the vitamin C in the diet (90%) comes from fruits and vegetables. However, since vitamin C is water soluble, cooking can destroy the vitamin C in a food.

Vitamin E, also known as alpha tocopherol, is a fat . Because vitamin E is found in oils, people who follow a low-fat diet may not get enough. Beta-carotene is a member of the carotenoid family. Found mainly in plants, carotenoids provide the vibrant red, yellow, green, and orange colors of fruits and vegetables, with carrots being a major contributor of beta-carotene. Typically, beta-carotene is a conditionally essential nutrient , but when one's intake of vitamin A is low, beta-carotene becomes an essential nutrient, meaning that it must be obtained from food and cannot be manufactured by the body.

Selenium is an essential trace mineral (trace minerals are needed only in small amounts). The amount of selenium found in food is directly related to the amount of selenium in the soil in which the food was grown. It is necessary for healthy immune function and is tied to killer-cell activity and antibody production. The many health benefits of the various antioxidants can be provided by a variety of food sources.

More and more functional foods contain combinations of various supplements. As popular as antioxidants are, an excess amount of them can be toxic. One reason to obtain antioxidants from food is that high doses may

actually promote free radical production, also known as pro-oxidation, increasing the chance for health problems. Those who may benefit most from antioxidants include people dealing with a lot of stress , dieters limiting their calories to 1,200 per day or less, people on a low-fat diet, smokers, older adults, and people with a family history of heart disease or cancer.

see also Functional Foods.

Susan Mitchell

Bibliography

Medical Economics Company (2001). PDR for Nutritional Supplements. Montvale, NJ: Author.

Internet Resources

American Dietetic Association. "Vitamin E: Disease Prevention for Your Good Health." Available from <http://www.eatright.org>

Doheny, Kathleen. "The Supplement Frenzy." Available from <http://www.webmd.com>

Antioxidants

Definition

Antioxidants are chemical compounds that can bind to free oxygen radicals preventing these radicals from damaging healthy cells.

Purpose

Preliminary studies have suggested that antioxidants are useful in a number of ways in regards to cancer. For instance, they may improve the effectiveness of chemotherapy , decrease side effects of chemotherapy and radiotherapy, and prevent some types of cancer. Sufficient epidemiological studies have shown that ingesting foods high in antioxidants, such as fruits and vegetables, can decrease the risk of many types of cancer. Studies have also found that cancer patients have lower levels of antioxidants in their blood. The American Cancer Society suggests eating five servings of fruits a day to decrease the risk of cancer.

Precautions

Studies of antioxidant supplements to decrease the risk of cancer have not been conclusive. Most antioxidant research has centered around vitamins A (and its provitamin, beta-carotene), C, E (alpha-tocopherol), and the trace element selenium. While some studies have shown positive effects for antioxidants in preventing cancer, they have been conducted mostly in underfed populations or persons otherwise deficient in these antioxidants. The CARET studies in the early 1990s found that if smokers take beta-carotene and vitamin A supplements they actually increase their risk of developing lung cancer. Rather than isolated antioxidants found in supplements, it may be the combination of antioxidants found in foods that are responsible for decreasing the risk of cancer. The American Institute of Cancer Research warns that antioxidant supplements cannot substitute for whole foods. Individuals who may want to consider supplements include those who are underfed, have certain medical conditions, chronic dieters, some vegetarians, some seniors, and newborns.

Concern has developed about potential negative interactions between high doses of antioxidants and chemotherapy. Anthracycline antitumor antibiotics used as chemotherapy act by creating free oxygen radicals to kill tumor cells through a process known as apoptosis. Although patients taking antioxidants may improve their tolerance to chemotherapy drugs, they may be decreasing the effectiveness of treatment and risking a recurrence of the tumor in the long run. This viewpoint is theoretical, however, and no clinical studies have as yet addressed it. Patients interested in using antioxidants during chemotherapy or radiotherapy should discuss this option with their physicians.

High doses of vitamins and minerals can be toxic. The National Academy of Sciences has suggested safe upper intake levels for adults for some antioxidants. These limits are 2, 000 milligrams of vitamin C per day from both foods and supplements combined, 1, 000 milligrams of vitamin E per day, and 400 micrograms per day of selenium from both supplements and foods. It is not known how higher levels than these will affect healthy persons.

Side effects of vitamin E overdose may include fatigue , intestinal cramping, breast soreness, thrombophlebitis, acne, and diarrhea , and increase in blood pressure in certain people. Blood clotting time has been shown to increase. Also, with 1, 800 IU per day, and vitamin E is antagonistic to iron and patients with anemia who are taking iron supplements should not take the two supplements at the same time. Vitamin E may also interfere with vitamin K. Selenium toxicity is characterized by dermatologic lesions; brittle hair, fragile or black fingernails, metallic taste, dizziness, and nausea.

Description

Free radicals are naturally produced in the body through the normal metabolism of amino acids and fats. These free radicals are unstable molecules that can freely react with and destroy healthy cells. They can bind to and alter the structure of DNA thus leading to mutations and eventually to cancer. Besides cancer, this oxidative stress on the cells can lead to heart, eye, and neurological diseases.

Glutathione, lipoic acid, and CoQ10 are antioxidants formed naturally by the body but their levels decline with age. Vitamins C and E are necessary antioxidants but not produced by the body and must be obtained from the diet. The most common antioxidants are the vitamins A, C, and E. Additional antioxidants are natrol, found in grapes and wine; selenium; and melatonin. Flavonoids consist of a large family of antioxidant compounds found in fruits and vegetables. Among the well-studied flavonoids in terms of cancer prevention are catechins from green tea, genistein from soy, curcumin from turmeric, anthocyanosides from blueberries, and quercetin from yellow vegetables.

Although controversy will surround the topic of supplemental antioxidants for some time, there is little if any controversy that dietary levels of antioxidants are useful in preventing cancer. Because of this evidence, the American Cancer Society suggests five servings of fruits and vegetables each day.

Resources

BOOKS

Moss, Ralph W. Antioxidants Against Cancer. Brooklyn, NY:Equinox Press, Inc., 2000.

PERIODICALS

Kelly, Kara M. "The Labriola/Livingston Article Reviewed."Oncology 13, no. 7 (1999):1008-1011.

Labriola, Dan, and Robert Livingston. "Possible Interactions Between Dietary Antioxidants and Chemotherapy." Oncology 13, no. 7 (1999): 1003-1008.

Lamson, Davis W, and Matthew S. Brignall. "Antioxidants in Cancer Therapy: Their Actions and Interactions with Oncologic Therapies." Alternative Medicine Review 4, no. 5 (1999): 304-329.

ORGANIZATIONS

American Cancer Society. <http://www.cancer.org>

American Institute for Cancer Research. 1759 R Street, NW, PO Box 97167, Washington, DC 20090-7167. (800)843-8114. <http://www.aicr.org>

National Academy of Science. <http://www.nas.edu>

OTHER

<http://clinical.caregroup.org/altmed/interactions/Nutrients/Vitamin_E.htm>

<http://www.medical.com.hk/english_site/pharmacy_site/vitamins_s/selenium/selenium_m.htm>

Cindy Jones, Ph.D.

KEY TERMS

Apoptosis

—A type of cell death. A mechanism by which one cell dies if it becomes severely mutated as a means of protecting the entire organism.

Cisplatin

—An anticancer drug.

Doxorubicin

—An anticancer antibiotic therapy. Its trade name is Adriamycin

Fluorouracil

—An anticancer drug. Its trade names include Adrucil, 5-FU, Efudex, and Fluoroplex.

Mutation

—A change in the genetic structure of the cell.

Oxidative stress

—A condition where the body is producing an excess of oxygen-free radicals.

antioxidant substance that prevents or slows the breakdown of another substance by oxygen. Synthetic and natural antioxidants are used to slow the deterioration of gasoline and rubber, and such antioxidants as vitamin C (ascorbic acid), butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA) are added to foods (see food additives ) to prevent them from becoming rancid or from discoloring.

In the body, nutrients such as beta-carotene (a vitamin A precursor), vitamin C, vitamin E, and selenium have been found to act as antioxidants. They act by scavenging free radicals , molecules with one or more unpaired electrons, which rapidly react with other molecules, starting chain reactions in a process called oxidation. Free radicals are a normal product of metabolism; the body produces its own antioxidants (e.g., the enzyme superoxide dismutase) to keep them in balance. However, stress, aging, and environmental sources such as polluted air and cigarette smoke can add to the number of free radicals in the body, creating an imbalance. The highly reactive free radicals can damage healthy DNA and have been linked to changes that accompany aging (such as age-related macular degeneration, a leading cause of blindness in older people) and with disease processes that lead to cancer, heart disease, and stroke.

Studies have suggested that the antioxidants that occur naturally in fresh fruits and vegetables have a protective effect. For example, vitamin E and beta-carotene appear to protect cell membranes; vitamin C removes free radicals from inside the cell. There is still some question as to whether antioxidants in the form of dietary supplements counteract the effects of increased numbers of free radicals in the body. Some scientists believe that regular consumption of such supplements interferes with the body's own production of antioxidants.

antioxidants Substances that slow the rate of oxidation reactions. Various antioxidants are used to preserve foodstuffs and to prevent the deterioration of rubber, synthetic plastics, and many other materials. Some antioxidants inhibit the oxidation reaction by removing oxygen free radicals. Naturally occurring antioxidants with this ability include vitamin E, β-carotene, and glutathione; they limit the cell and tissue damage caused by foreign substances, such as toxins and pollutants, in the body.

antioxidant A substance that retards the oxidative rancidity of fats in stored foods. Many fats, and especially vegetable oils, contain naturally occurring antioxidants, including vitamin E, which protect them against rancidity for some time. Synthetic antioxidants include propyl, octyl, and dodecyl gallates, butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT). See also antioxidant nutrients; induction period.

anti-oxidant A compound, usually organic in nature, that prevents or retards the oxidation by molecular oxygen (autoxidation) of materials such as food, rubber, and plastics. It acts by scavenging the free radicals generated in autoxidation chain reactions, and thus provides an alternative oxidation pathway. It does not act indefinitely as it is destroyed in the process.

anti-oxidant A compound, usually organic in nature, that prevents or retards the oxidation by molecular oxygen (autoxidation) of materials such as food, rubber, and plastics. It acts by scavenging the free radicals generated in autoxidation chain reactions, and thus provides an alternative oxidation pathway. It does not act indefinitely as it is destroyed in the process.

an·ti·ox·i·dant / ˌantēˈäksidənt; ˌantī-/ • n. a substance that inhibits oxidation, esp. one used to counteract the deterioration of stored food products. ∎  a substance such as vitamin C or E that removes potentially damaging oxidizing agents in a living organism.

antioxidant (anti-oks-i-dănt) n. a substance capable of neutralizing oxygen free radicals, the highly active and damaging atoms and chemical groups produced by various disease processes and by poisons, radiation, smoking, and other agencies. Antioxidants include vitamin C (ascorbic acid), vitamin E (tocopherols), and beta carotene.