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What We Know and Don't Know About Antioxidants and Cancer

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By: Jerah Thomas, M.P.H., Peiying Yang, Ph.D., Richard Lee, M.D., and Lorenzo Cohen, Ph.D.

Antioxidants_small.jpgThe National Cancer Institute defines an antioxidant as: "a substance that protects cells from the damage caused by free radicals (unstable molecules made by the process of oxidation during normal metabolism)."  

Antioxidants neutralize the electrical charge of free radicals, which damage DNA by taking electrons from other molecules. Free radical damage has been linked to aging and a number of diseases including the development of cancer. Antioxidants may slow or possibly protect against cancer.

Laboratory studies have reported evidence supporting the role of antioxidants in cancer prevention. However, clinical trials have shown no benefit of antioxidant supplementation. The Women's Health Study (WHS) and The Physicians' Health Study II concluded Vitamins E and C did not protect against cancer development. The Selenium and Vitamin E Cancer Prevention Trial not only reflected similar results, but also reported a slight non-significant increase in prostate cancer incidence among the men in the study who were taking vitamin E supplements. Similarly, the role of antioxidants in augmenting the effects of chemotherapy or radiation therapy remains controversial.

As clinical trials of antioxidant supplementation are inconsistent, and the efficacy during treatment is still being debated, we recommend obtaining antioxidants through food sources. Research suggests that diets containing antioxidant-rich fruits and vegetables may lower the risk of certain cancers

Some recommended antioxidant-rich foods:

Foods containing antioxidant-based vitamins and minerals
•    Beta-carotene - typically found in orange-colored foods such as sweet potatoes, carrots, squash and mangos. Spinach, kale, broccoli, and collard and turnip greens also are good sources.
•    Selenium - brazil nuts and seafood such as tuna and cod.
•    Vitamin A - leafy greens such as spinach and kale, carrots and cantaloupe.
•    Vitamin C (ascorbic acid) - citrus fruit such as oranges, grapefruit, red and green peppers, kiwifruit, broccoli and strawberries.
•    Vitamin E (alpha-tocopherol) - wheat germ, sunflower seeds, almonds and cooked tomatoes (tomato paste, tomato products, etc.).

Foods rich in naturally bioactive antioxidants
•    Polyphenols (flavanoids, catechins and anthyocyanidines) - soy, green tea, dark chocolate, plums, cranberries, blueberries, black raspberries, blackberries, strawberries, apples and nuts (hazelnut, pecans and pistachios).
•    Glucosinolates (isothiocyanates, thiocyanates and nitriles) - cruciferous vegetables such as watercress, broccoli, cabbages, cauliflower, brussel sprouts, and kale.
•    Resveratrol (phytoalexin) - grapes, cranberries, blueberries and peanuts.
•    Lutein - leafy greens such as spinach, kale and collard greens, broccoli, kiwi and red grapes (high in lutein).
•    Lycopene - cooked tomatoes (tomato paste, tomato products, etc.), water melon and apricots.

Resources

Office of Dietary Supplements: Dietary Supplement Fact Sheets

Should supplemental antioxidant administration be avoided during chemotherapy and radiation therapy? (NCI)

Impact of antioxidant supplementation on chemotherapeutic toxicity: a systematic review of the evidence from randomized controlled trials

Antioxidants and other nutrients do not interfere with chemotherapy or radiation therapy and can increase kill and increase survival

Antioxidants and other nutrients do not interfere with chemotherapy or radiation therapy and can increase kill and increase survival, Part 2.

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2 Comments

While I would agree that some studies have shown isolated and synthetic extracts may offer no benefit to cancer patients, it would be nice to test to see if natural "whole plant" compounds would offer some benefit. New-Chapter is a company that offers these types of compounds and whole plant extracts. Hypothetically, it makes sense to use a whole plant extract, as all of the compounds work together. If one takes a high dose of one isolated extract, i.e. Beta Carotene (there are hundreds of different Carotenoids) or Vitamin E (there are 8 different forms or isomers of Vitamin E) it makes sense that the efficacy will be poorer than those of whole plant compounds.

What would really be nice would be some kind of statement/stance/opinion from MD Anderson about antioxidants' effect on chemo and/or radiation. Needn't be written in stone by any means, but SOMETHING. To date I see nothing. Frankly it's extremely disappointing from the leading cancer center in the world.

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