Antioxidants Health Article

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.