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

Vitamin D and Dog Cancer

Updated: October 25th, 2019

Dog lovers will do anything they can to help their dog with a cancer.  And you should! This can be one of the hardest times anyone will face.

Many times the effort helps, and other times it may not.

This, of course, is not due to any ill intention on the part of the dog’s human.  Rather, it is simply because there is inadequate use able information out there.

Take, for example, the use of vitamin D supplements for dogs with cancer.

Well yes, sure, cancer in the test tube will undergo apoptosis (normal, healthy end of life cycle) when exposed to the body’s active form of vitamin D.

And yes, some cancer cells have little empty “locks” on the outside of them (receptors) that fit the vitamin D “key”.  When the key fits the lock (vitamin D binds the receptor on the outside of the cancer cell), the cancer cell commits suicide.

So, doesn’t it make sense that if a dog were to get cancer, giving vitamin D would be a smart move??

Well, not really, not quite.

First,  remember we always have to ask whether the stuff in the pill gets all the way to the cancer in the body.  We give our dog a pill, and the active ingredients have to be taken into the blood by getting through the wall of the intestine, making it past the liver, escaping excretion into the urine, getting back out of the blood, and bathing the cancer cells in the tumor.

That’s a pretty long trip.

Turns out that it is hard to get the vitamin D all the way to the cancer cells. Blood levels of the most active form of vitamin D (calcitriol), are mainly produced by exposure to direct sunlight on the skin, not by taking it by mouth to get high blood levels.  Look for yourself.

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Of course, if you take enough, you can get high blood levels that can help with cancers in the body.  The problem is that you also may get dangerously high blood calcium levels.  Active vitamin D boosts blood calcium levels.  When you get excessively high calcium levels, bad things start to happen (kidney injury, heart problems, and more).

So we have a quandary.

What to do?

Well, big pharma is trying to make drugs like active vitamin D for cancer, but without the high blood calcium bit. Here is some info about that. The problem is that they are not available yet.

So can we do anything?

Yes, two things. First, get your dog into the sun, with a few exceptions.  Sunlight has a dramatic effect on active vitamin D levels in the blood. We are talking about direct sunshine a couple of times a week, about 10-20 minutes each time.

A word of caution: do not overheat your dog!! Long hair, short muzzles, breathing problems, obesity, and other issues can increase heat stroke chances. Check with your vet.

Another word of caution:  squamous cell carcinoma, as well as hemangiosarcoma of the skin, have increased risk with sun in dogs.  Don’t do a lot of sun if your dog has these cancers. Get a full spectrum lamp for seasonal affective disorder in people.

For more helpful tools and information, get a copy of the Dog Cancer Survival Guide

By the way, do not worry if your dog has melanoma.  This cancer has not been shown to have a link with sun in dogs.

The second thing you can do is make sure your dog is getting maintenance vitamin D levels. My  personal opinion supports a balanced multivitamin for dogs with cancer.  It has been shown that vitamin D deficiency does bad things like increase certain  cancers, like colon cancer in mice.  Read about it here.

So get your dog some sun and his or her normal, dietary level of vitamin D. Don’t bother with the high doses for dogs with cancer.


Dr D

Leave a Comment

  1. Dick G on March 21, 2014 at 12:51 pm

    I have read what I consider some reliable papers that agree with “Anon”. Here’s a link for an explanation of why very little 7-DHC is produced in the skin of dogs and cats. Not sure who is right here. Also I thought the Vit. D Receptor is in the nucleus of the cell not on the outside. Let me know if I’m wrong about that or if it is different in dogs than in humans.

  2. Anon on December 12, 2012 at 1:40 am

    Cats and dogs cannot synthesize Vit D from sunlight – do some basic research from multiple sources.. check Wikipedia, ask a vet that sounds like they have a clue..

    • Dr. Demian Dressler on December 26, 2012 at 12:14 pm

      Dear Anon, one of the problems with the internet is that it may not always yield the best information. Most mammals are able to synthesize (active) vit d3 from 7-dehydrocholesterol in the presence of ultraviolet B light (such as that emitted by the sun), including dogs and cats. This occurs in the skin. Perhaps a veterinary clinical nutrition text would be a source you might want to reference.

  3. jennifer skyler on June 29, 2012 at 12:31 pm

    Sun protection is important, especially when you have fair skin like i do. I found this color changing bracelet by SolarActive that changes color in the sun when the UV rays hit it. This is one of the ways i stay sun aware and sun safe. The bracelet seems to change colors faster or slower depending on how much UV the sun is emitting that day. You could probably even rig up your dog with one of these! lol
    They have color change tshirts and color changing beads as well. I got it at the SolarActive website here: I always recommend my friends to get products like these since they really help to be sun aware. Thanks for the blog and keep up the good work I love reading! 🙂

  4. L. Sledge on June 19, 2012 at 6:10 pm

    see above

  5. Victoria Cobb on March 29, 2010 at 7:07 am

    Dear Dr. Dressler, I have been told my 13 year old dog has stomach cancer. I would appreciate any advice! Thank you, Victoria Cobb

  6. Ollie on June 21, 2009 at 7:12 am

    My jack russell has bladder cancer ( a seed type). He had surgery in February 2009 but the cancer returned within a month & has increased in size. He has difficulty urinating but other than that he still chases squirrels & enjoys his daily runs, meals & visits from people. He takes 2MG/ML meloxicam 2 thyro tabs for his thyroid, 2 trilostane
    for cushings disease. I have recently introduced 1000 IU vitamin D in a 50 ML dropper which I am giving once daily.
    Would that be dangerous to a dog with cushings disease?

    • Dr. Dressler on June 28, 2009 at 8:59 am

      Good question!
      I will address vitamin D at this weeks webinar:
      Thank you
      Dr D

      • Dr. Dressler on June 28, 2009 at 9:15 am

        FYI the webinar is recorded so you can listen later,

  7. Vitamin D and Dog Cancer | Weak Bladder on June 7, 2009 at 3:30 pm

    […] Vitamin D and Dog Cancer Posted by root 5 hours ago Blood levels of the most active form of vitamin d calcitriol are mainly produced by exposure to direct sunlight on leave a comment name mail will not be published website frank peel on bladder and prostate cancer neutering male dogs increases risk flexx t Discuss  |  Bury |  News | Vitamin D and Dog Cancer […]

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