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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

Anti-oxidants versus Pro-Oxidants

Updated: January 7th, 2019

A reader asked an interesting question recently that I thought would make a good post. The question involved the use of antioxidants, either for dogs with cancer or to help prevent cancer.

Lets get an overview to clarify this frequently-muddied picture.

A free radical is a reactive molecule that tends to damage cell parts.  When DNA is damaged, this can mean damaged genes.  If the genes controlling cell multiplication are harmed, cell growth can get stuck in the “on” position.

When cell growth is stuck “on”, this spells cancer.

Cancer cells are very active doing all this growing.  One of the by-products of all this activity in an increased load of free radicals within the cancer cell.

Cancer cells are not good at handling much more free radicals, since they already have more in them than normal cells.

The body is able to quench free radicals with substances called antioxidants.  Antioxidants lessen the amount of free radical-induced injury.

A pro-oxidant has the opposite effect.  It tends to increase the amount of free radicals.

Since pro-oxidant strategies increase free radicals, it would seem that the way to kill cancer cells is by bombarding them with pro-oxidants.  This would lead to  more free radicals within cancer cells, and injury to the cancer cells.

The mechanism of many chemotherapy drugs, as well as radiation, in destroying cancer cells is by causing  free radical increase within cancer cells.  This is the same mechanism in many of the apoptogens discussed in The Dog Cancer Survival Guide.

Get a copy of the Dog Cancer Survival Guide for more helpful information and tools

Now, healthy cells also suffer when there is free radical excess.  It is just they have more of a natural buffer within them than the free-radical filled, madly proliferating cancer cells do.

If the natural body buffers are depleted, this can lead to lack of overall body health in the fight against cancer.  That is why maintenance levels of certain antioxidants actually help during the fight against cancer.

We want to preserve overall body health, and minimize side effects of chemo and radiation toxicity. Many chemo and radiation side effects are due to injury of normal body cells by the free radicals caused by these treatments.  Here is a good read on the topic.

Maintenance antioxidants help, and this has been evaluated and shown to be accurate, even when these antioxidants were used along with chemotherapy.

However, only some so-called antioxidants should be used in high levels (way above maintenance levels) during cancer treatment with chemotherapy or radiation. At high levels, these substances no longer have antioxidant effects.

Rather, they typically  have pro-oxidant effects.  Selenium, EGCG, IV vitamin C and others are like this. Some so-called antioxidants at high levels have other ways of killing cancer cells, like inhibiting certain enzymes (curcumin inhibits topoisomerase II).

For more information to help your dog with cancer, get a copy of all 47 informative webinars!

If we are relying on conventional care, we don’t want to create abnormally high antioxidant effects in the body, as there could be interference with  radiation and chemotherapy.  Since these tools work by increasing free radicals, excessive antioxidants may decrease efficacy. Read more here.

It becomes clear that dosages are a central issue with antioxidants.  Maintenance levels and high levels do different things.

What about cancer prevention and longevity?

When a dog gets cancer, it is the end result of many damaging events. It likely takes a lifetime of steps, which is why cancer is more typical in older dogs.

It has been said that there are many cancer cells developing in the body daily. True.  Developing, but not yet developed.  That means they are not actual cancers yet.  They are cells on their way to becoming cancer cells.

In the path to true, clinical cancer (the end stage), damaging steps are free radical injury to genes controlling cell growth.  There needs to be multiple hits over time in certain locations on the DNA for the damage to finally create a cell growth signal stuck on “on”.

Thus, before true, clinical cancer actually develops,  you want antioxidant effects, not pro-oxidant ones, in general.

In contrast, after cancer clinically develops, one could choose pro-oxidants as the anti-cancer weapon.

I hope this helps everyone wondering about vitamins, antixodants, and cancer.


Dr D

Leave a Comment

  1. Diana Couture on September 12, 2013 at 3:54 am

    Excellent article. Searched for info a long time regarding this issue. Thought antioxidants would help get my dog through treatment but now know they would “undo” the purpose of chemo with lomustine.

  2. Audrey on August 13, 2013 at 3:30 am

    Dr. Dressler,
    My 11.5 year old Dalmation/Lab mix had an emergency splenectomy 16 days ago. It was determined by biopsy that he had HSA and that it had spread to the liver. The liver spots are small at this time. I immediately started him on I’m Yunity and Yunnan Baiyao as the oncology appointment was not for two weeks after surgery.
    We started him on doxyrubicin yesterday. The oncologist wants to do treatments every two weeks for the first three treatments.
    My question to you is in reference to the Apocaps, which I ordered from Amazon and should arrive today. The oncologist told me not to use Apocaps until the chemotherapy was finished due to the inclusion of Vitamin C as a major indgredient in the Apocaps. She feels that the anti-oxidant effect of Vitamin C is contraindicated for the doxyrubicin.
    I also see that in your practice you routinely use Apocaps during chemotherapy. I do not want to go against my oncologists wishes, however I also want to do what is best and will give the best overall results to my dog. Do you have any information I can pass on to my oncologist to help with this matter?

  3. roxanne warner on October 15, 2012 at 9:26 pm

    Dear Dr Dressler,
    my 9 yr old irish setter was diagnosed with osteosarcoma oct 10,2012. i started him on artemisinin 100mg administered in a pill pocket and empty stomach 8am and again at 10:30pm….i’ve started adding another pill at 11:30pm. i’m doing the artemisinin research on my own and spending most days all day long reading. the dog weighs 70 lbs, and is not a candidate for amputation due to being a severe abuse rescue that required 2 TPLO’s on both back legs……otherwise the dog is in really good health. he lives in the house with 2 other irish setters, and during the rainy season all 3 of them are couch potatoes…in good weather they have access to 3/4 acre of lawn with shade trees. i’m guessing at the dosage for the artemisinin and i’ve also ordered and will hopefully start tomorrow the synthetic form with the iron in it..50mg Hepalin . i realize the dog more than likely has a zero chance of survival, (i’ve lost a dog to this disease in 2001), but if i could just buy him some time with relative freedom from pain would really to do that. i don’t have a holistic vet in my area, and the vets i use sent the dog home to wait euthanasia.
    any advise you could send my way i would be extremely grateful for. especially info on dosing, frequency, downtime from the drug,etc…..
    thank you,

    the dogs diet consists of chicken no-grain natural balance kibble and merrick 97% meat canned…they get kingdom pets costco chicken jerky for treats

  4. judy on November 30, 2011 at 5:56 am

    so giving vit c by mouth is just wasting my money. My Springer Spanial is 8 and has lymphoma. it has been 7 weeks since I notice the lump and took hime to the vet.

    • Dr. Demian Dressler on December 4, 2011 at 4:28 pm

      Dear Judy,
      I believer there is very little benefit to oral vit C. On the other hand, IV vitamin C and the other steps in the Guide can help…
      Dr D

  5. Elaine on December 9, 2010 at 10:05 am

    Dr. Dressler,

    I have been reading your book, in particular the plant based cancer fighting supplements section. I have a question regarding the use in our case, I hope you would be able to share some insight. You mentioned in the book that some of those supplements given at high doses become pro-oxidants, and they in turn increase the amount of free radicals in body, including cancer cells (and damage them).

    I have an 11 year old Airedale who has been suffering from uncontrolled Cushing’s disease since June 2010. Her overall health deteriorated, and she was dx with a Grade 1 Soft Tissue Sarcoma in her left thoracic region in November 2010. Tumour (size of a jelly bean) removal, margin surgery performed a week after dx. Pathology came back showing we did not achieve wide margins from one of the planes. From my understanding, this is a locally aggressive tumour that recurs at the same location, and doesn’t tend to metastasize. Even with the unclean margin, I was given an estimated recurrence at 3-4 years post surgery (Grade 1, low mitotic index).

    So my question is, would pro-oxidant effect be favourable in the case where most cancer cells have been removed (but not complete), and doesn’t tend to metastasize? I guess in my layman way of thinking, would there be not enough cancer cells for the extra free radicals, and the free radicals actually cause harm to healthy body tissue? (We started Trilostane for Cushing’s December 2010)

    Thank you so much for writing such a wonderful book and all the blog posts! You have helped so many of us desperate God owners, I mean, doG!


  6. Carla Benoist on January 21, 2010 at 8:07 am

    Wow. My greyhound, Silver, had a mast cell tumor removed from his rear right leg last April ~ 10 months ago. I’ve cut way back on his carbs, but because he has “slightly challenged” kidney function (he was losing too much protein in his urine) I am also supposed to keep his protein down as low as possible. That in itself is a juggling act.

    I give him 2 Co-Q10+ capsules a day (Fish oil, CoQ10 and vit. E) and a Marin tablet, plus he is using the Chinese Herbals Power Mushrooms and Blood Palace for follow up in lieu of any Chemo. So far, so good. I’m currently using Dr. Harvey’s complete Veg-to-Bowl dehydrated fresh dog food with a very small amount of good quality kibble, grass fed beef from a local farm and occasionally Eagle Brand canned (now Holistic Select). It does get confusing, and sometimes expensive (I have 4 sighthounds and am on fixed income) — finding the right balance between low carb and low protein and now questioning his supplements is — well, distressing. Love to hear a response on this.

    • Dr. Dressler on January 22, 2010 at 9:44 pm

      Dear Carla,
      You are in the land of medicine: the gray zone. More data needs to be considered. First, if your dog has a Hard to Cure Cancer, you may want to consider a more Full Spectrum approach than a replacing approach (supplements instead of chemo). I am wondering about the logic in the CoQ10 selection and in some of the other choices. Why not pick some supplements that have some more direct evidence against cancer cells? Similarly, why not some support to stabilize mast cells so they don’t secrete as much histamine? Although I do not have a cure for systemic cancers, it may be worthwhile to consider some of these questions. Luteolin, EGCG, artemisinin, cimetidine, ginger, slippery elm…just to name a few that pop into mind for dogs with mast cell tumors. I blogged on these so you can search for them and wrote about them in my e-book.
      Anyway, to answer your question directly, you may want to find out whether the urine protein was tested using a urine protein/creatinine ratio test. Urine protein readings in a normal urinalysis have lots of positive protein readings that will have nothing to do with kidney function. Perhaps there is more evidence for kidney disease in your dog that I don’t know about?
      Bottom line, try to get an idea of the objective severity of the two conditions from your vet, which I cannot do. Which is worse? Then, go with that.
      Hope this helps,
      Dr D

  7. Vitamin C and Dog Cancer Update on December 6, 2009 at 2:38 pm

    […] Vitamin C is known as an anti-oxidant.  While it is at lower doses, the anti-cancer effects at the needed super-doses are actually pro-oxidant. (For more  on these concepts, click here) […]

  8. sandra lovitz on July 3, 2009 at 2:25 pm

    Does anyone know about K-9, transfer factors for treatment
    toward getting a dog’s immune system in better shape to fight
    cancer? The surgeon for my dog was not very impressed with
    this information…n

  9. sandra lovitz on June 30, 2009 at 1:58 pm

    My dog recently had a pheriphial tumor on his leg removed.
    No rad. or chemo… now what for his diet.. I took all grains
    away. Do you know of transfer factors?

  10. Chris Ambrose on June 29, 2009 at 6:57 pm

    I recently lost a dog to mailgnant histiocytosis and I have her half sister. I really want to help her not get cancer & wonder what food or suppliment you would suggest as a preventative.Thank you for any suggestions…Sincerely, Chris Ambrose

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