More Evidence Antioxidants May Increase Cancer Risk

I’ve written before about why the near magical status of antioxidant supplements, supposed to be miraculous in preventing or treating disease and aging, is inconsistent with science and not supported by good evidence. Antioxidants in general, and specific supplements like resveratrol (1, 2, 3) and Vitamins C and E (4, 5, 6), and even antioxidants in foods, have proven far less miraculous than hoped or claimed by alternative practitioners, and some have even proven harmful. Some studies intended to investigate whether antioxidant vitamins can prevent or treat cancer have actually found an increase in risk. A new laboratory study provides a bit more evidence concerning the potential risks of such chemicals.

LeGall K., et al. Antioxidants can increase melanoma metastasis in mice. Science Translational Medicine. 2015;7:308.

The article is behind a paywall, but a description of the results published elsewhere suggest that antioxidants can promote tumor growth and invasion under some circumstances. This is consistent with previous research, though the actual effects in patients with naturally occurring disease is not clear.

These results don’t mean antioxidants might not have value in prevention or treatment of some diseases. But like anything which affects the complex physiological processes of the body, they can have unintended consequences. This means they must be used rationally and with appropriate research evidence to support their use, not treated as magical and safe panceas.



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9 Responses to More Evidence Antioxidants May Increase Cancer Risk

  1. LoisLame says:

    What are your thoughts on the antioxidants added to pet foods? I noticed Hills constantly advertises about beta-carotene and Vit E in their formulations, but it makes me nervous…

  2. skeptvet says:

    Often I believe these are added as preservatives to retard spoilage, especially given the hysterical bad press often given to “artificial” preservatives used to prevent oxidation. I doubt the amounts in food are high enough to cause any harm, compared to the taking of specific supplements above and beyond dietary intake, but I am also not convinced there are major benefits.

  3. LoisLame says:

    It appears that they are adding antioxidants above and beyond preservative levels. Many of the “advanced” and prescription Hills formulas seem to have higher Vit E and A levels than their basic lines; Purina Pro Plan has added additional amounts to their toppers; Iams is claiming that their “most advanced” dry formula has “twice the antioxidants, vitamin E, and beta-carotene (compared to Iams ProActive Adult) to promote a strong, healthy immune system.”

    I’m not part of the veterinary community (yet) – have you heard from any of these companies in regard to their antioxidant additions and any research they’ve actually done to show results? I’m also really curious about Hill’s adding cranberry, spinach, and other vegetables to some of their foods. I trust Hill’s in general when it comes to EBM but I have no idea if these additions actually have any science to back the use of these ingredients up, or if they’re just caving to faddish pressure.

  4. art malernee Dvm says:

    . I trust Hill’s in general when it comes to EBM but I have no idea if these additions actually have any science to back the use of these ingredients up, or if they’re just caving to faddish pressure.>>>

    I just got 2 hours of required by law CE sponsored by Hills this month and when they ask for the RACE approved CE feed back I put down on the sheet no prospective randomized trials to support the lecture. If you use food as a “preventative” you need these trials. Otherwise you violate the “father of evidence based medicine law ” about using treatment as a prevention. The FDA needs to do a better job regulating dog food promotions

  5. v.t. says:


    Beyond skeptvet’s comments on the additives, I agree with you on Hill’s recently adding ingredients that make you go, hmmm? Spinach? Let me guess, because it’s a dark leafy green? (really, I have no clue why anyone thinks a cat needs spinach). Cranberries (or extract) have been added to all sorts of pet foods for almost a decade now, presumably extrapolated from human studies regarding urinary tract health (I’m not aware of anything useful or recent in animal studies), and as for vegetables, most likely no harm for most as long as there is a proper formulation taking into account overall nutrient profile etc.

    IMHO, Hills is following the fads. Too bad really, because they’re among only a few who actually seemed to care about the science that goes into pet food.

  6. skeptvet says:

    I ran Lois’ question past a couple of nutritionists I know, and they gave me some interesting responses and some research work to read through. Hopefully, I’ll get around to a post about antioxidants in pet nutrition sometime soon.

  7. LoisLame says:

    Thanks so much skeptvet! I eagerly anticipate your write up. 😀

  8. mary Anne Whitonis says:

    Antioxidants covers a wide spectrum and most people think of antioxidants as the popular ones such as vitamin c, etc. A truly formally western educated holistic veterinarian who uses integrated medicine uses far more than vitamin c and vitamin e in their practices. The vet I use from Hawaii has several dogs in the practice as patients currently who had tumors in their lung for over two years and with his treatment plan is still going strong and thriving to this day. It is why you defer to the experts and not the hinky dinky pot shop who simply dabble in herbs, etc.

  9. skeptvet says:

    Of course, there are many antioxidants other than Vit C and E. The point you seem to have missed is that there is no guarantee the others will be safe and effective any more than these vitamins turned out to be. The devil is in the details, so calling something an anti-oxidant tells us nothing about whether it is beneficial, harmful, or neutral. And primary lung tumors are slow-growing, often taking many years to cause clinical symptoms, so I’ve seen the same clinical results without doing any alternative therapies. Once again, anecdotes prove nothing.

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