Antioxidants: friend or foe?

Amy Thomas Health Guide
  • For the past decade we've heard all about the amazing benefits of antioxidants; as a result many of us try to incorporate into our diets the recommended deeply colored fruits and vegetables chocked full of anti-aging, heart-healthy, and life-prolonging metabolites. But recently, the all-healing properties of antioxidants are in question, and some scientists now suggest they may increase the risk of cancer and cause harm in people being treated for cancer. The messages are conflicting, and many people are left wondering what to believe.


    Anti-oxidants are found naturally in a number of deeply colored foods-dark red cherries and tomatoes, orange carrots, yellow corn and saffron, and blueberries. Their reported health benefits have led to the increasing use of certain nutritional supplements known to have strong antioxidant activity, including β-carotene, selenium, lycopene, and vitamins A, C, and E.

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    Research reports have posed concern that cancer cells could use antioxidants, particularly vitamin C, to repair themselves and guard against radiation and chemotherapy damage. Studies investigating whether antioxidants reduce the benefit of cancer treatment have provided mixed results, so the Mayo clinic performed a systematic review on the topic. Although the review doesn't answer all the questions, the scientists did determine that antioxidants do not lower the overall risk of cancer, and some antioxidants may increase cancer risk, so at this time, supplementation is not recommended until further research is available.


    While we wait to hear about the value of other antioxidant supplements in cancer prevention and treatment, at least one popular supplement has been identified as dangerous. Beta carotene, the orange photosynthetic pigment in carrots that is the precursor to vitamin A, is linked to an increased risk of lung cancer and increased cancer mortality. Most studies report the risk associated with taking at least 30 mg of the supplement daily. Unlike the supplements, foods rich in beta-carotene have not been linked to increased cancer risk and the amount of beta-carotene from consuming 5 servings of fruits and vegetables per day is still recommended to maintain adequate levels of vitamin A. (1.8 milligrams or 1800 micrograms) Beta-carotene is also found in sweet potatoes, carrots, kale, spinach, turnip greens, winter squash, broccoli, romaine lettuces, cantaloupe, thyme, cilantro, and collard greens.


    On evaluating other antioxidant supplements, the Mayo review suggested that selenium, a micronutrient found naturally in nuts, cereals, meat, fish, and eggs, might have beneficial properties for cancer patients, although these findings are not confirmed. Selenium will not be recommended for general use until more evidence is available. While the report found neither benefit nor harm from Vitamin E supplements, too much vitamin E is known to cause stomach upset, diarrhea, and bleeding, and could exacerbate symptoms often already a problem for people being treated for cancer.


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    These reports are not closing the door to use of antioxidants during cancer treatment. Many antioxidants have shown promise in preventing certain side effects of chemotherapy and radiation, warranting further study of their risks and benefits. Vitamin A and E may prolong survival in lung cancer patients being treated with cyclophosphamide; glutathione is being studied as a protective agent for cyclophosphamide-related bladder damage and oxaliplatin-induced neuropathy; and vitamins E and C may offer protection against radiation proctitis in patients with prostate, cervical, and endometrial cancer.


    In summary:

    • Antioxidants do not lower the risk of cancer
    • Antioxidant supplements, but not those occurring naturally in foods, may reduce the efficacy of certain cancer treatments
    • Beta-carotene supplements should be avoided, especially in smokers
    • Continue to eat the recommended 5 daily servings of fruits and vegetables per day to get adequate vitamins, pro-vitamins, dietary minerals, and fiber
    • Tell your doctor if you are taking any nutritional supplements
Published On: February 07, 2008