There is a raging debate about whether or not cancer patients should receive antioxidants during radiation and chemotherapy treatment. In the human literature, one faction insists that antioxidants should be avoided during cancer treatment. They cite diminished response to cancer therapy.
The opposing group believes that antioxidants should be used because they enhance cancer kill rates and decrease toxicity to the body. As more dogs undergo treatment for cancer, this debate has moved into the veterinary world.
Cancer treatments such as radiation and some forms of chemotherapy deliberately cause oxidation in cancer cells in order to kill them. Assuming antioxidants stop this reaction, they could protect cancer cells and therefore interfere with therapy.
The antioxidants’ effect on cancer-cell survival has been confirmed in the laboratory. Human cancer cells take in more vitamin C than normal neighbouring cells, and vitamin C helps them resist oxidative injury. As well, studies show that low doses (not high doses) of specific antioxidants, in certain circumstances, may stimulate cancer-cell proliferation.
The counter argument is that by making the body feel better and its immune system more robust, supplements can help it fight cancer more effectively. Products designed to lessen the side effects of cancer therapy, whether they are dietary supplements, herbal mixtures, or vitamin combinations, often have strong antioxidant properties.
People promoting antioxidant products say they improve immune function, increase the tumour response to radiation and chemotherapy, and decrease toxicity to normal cells. If they are right, supplementation is worthwhile.
In a review of 50 human studies involving 8,521 patients, the overall consensus was that non-prescription antioxidants and other nutrients do not interfere with cancer therapy. Furthermore, they were found to enhance the killing of cancer cells, decrease side effects and protect normal tissue from the deleterious effects of the cancer therapy. In 15 studies, patients who took these supplements had an increased survival time.
If we extrapolate these results to the canine world, it suggests supplements should be given to dogs undergoing cancer therapy. The question is, which ones?
According to Dr. Shawn Messonnier’s book Preventing and Treating Cancer in Dogs, milk thistle, also known as silymarin, is an antioxidant that protects the liver. It also has a direct effect against certain cancers. He recommends 100 milligrams for each 25 pounds body weight, twice daily.
Other supplements with antioxidant effects include vitamins A, C and E, as well as the minerals selenium, manganese and zinc. Gingko biloba, grape seed extract and pycnogenol have also been used. To establish the correct dose for your dog, talk to your veterinarian.
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