Vitamin D for Dogs and Cats: More Than Strong Bones

• Food, not sunshine: Dogs and cats make very little vitamin D from sunlight, so their diet is their main source.
• Ontario pilot results: In ImmunoCeutica's 2024 pilot, all 11 dogs and 10 cats tested below 100 ng/mL, a level some researchers consider optimal. There is no agreed standard yet.
• Test before you supplement: A vet blood test is the only way to know your pet's level, and too much vitamin D can be harmful, so always follow the recommended dose.

Your dog can nap in a sunbeam all afternoon and still make very little vitamin D. Unlike people, dogs and cats can't count on sunshine for this nutrient. Most of it has to come from their food.

When we think about vitamin D, we usually think of sunshine and strong bones. For our pets, the story is different, and vitamin D does far more than build bones.

Why Do Dogs and Cats Need Vitamin D?

Vitamin D helps the body manage calcium and phosphorus, two minerals essential for healthy bones and teeth.

This matters most while pets are growing. Puppies and kittens need enough vitamin D for their skeletons to develop normally. Adult and senior pets still depend on it to keep bones healthy and to help the body handle calcium properly.¹ ²

Vitamin D's job doesn't stop at the skeleton. Researchers have found vitamin D receptors, the "docking stations" cells use to respond to vitamin D, in tissues throughout the body. That suggests vitamin D takes part in a wide range of the body's processes.³

Does Vitamin D Affect My Pet's Immune System?

Vitamin D isn't just about bones.

Veterinary research is exploring how vitamin D may help regulate the immune system and inflammation. Cells of the immune system carry vitamin D receptors, which suggests vitamin D may help keep immune responses in balance.⁴

To check vitamin D status, researchers measure a form called 25-hydroxyvitamin D in the blood. It's the same marker used in human vitamin D tests; in this article we simply call it "blood vitamin D levels."

One study of dogs with long-term digestive (gut) problems found that dogs with lower blood vitamin D levels showed more signs of inflammation, both in the gut and throughout the body.⁴ That's a link, not proof that low vitamin D caused the inflammation, but it's one reason researchers are taking a closer look.

What Does Research Say About Vitamin D and Cancer in Dogs?

Researchers are also studying possible links between vitamin D and cancer in dogs. This research is early and shows associations only. No study shows that giving vitamin D prevents or treats cancer in pets.

One study found that among dogs with bleeding into the abdomen, those with lower blood vitamin D levels were more likely to have cancer as the cause.⁵ Vitamin D receptors have also been found in osteosarcoma, a common bone cancer in dogs.⁶

Another study reported lower blood vitamin D levels in dogs with osteosarcoma and lymphoma than in healthy dogs,⁷ while a separate study found no difference between dogs with osteosarcoma and healthy dogs of similar age and size.⁸ In short, the science is still developing.

Can't My Dog and Cat Just Get Vitamin D from the Sun?

People make vitamin D3 in their skin when UVB sunlight hits it. Dogs and cats can make very little this way, so their food is their main source.⁹

That means what's in the bowl really matters. In a study of 320 healthy dogs, blood vitamin D levels varied depending on which brand of commercial food they ate, and dogs on homemade diets varied even more.¹⁰ The amount of vitamin D in the food was a key driver of each dog's level.¹⁰

Cats are similar. Research in healthy adult cats found that the vitamin D they eat strongly influences their vitamin D status.¹¹

What Did We Find in Ontario Pets?

In 2024, ImmunoCeutica ran a small pilot study measuring blood vitamin D levels in dogs and cats in Ontario. The results are preliminary and unpublished, but they raise a fair question: are our pets getting enough? [Add what the pets were eating, if known.]

	Dogs	Cats
Number tested	11	10
Average blood vitamin D level	24 ng/mL (about 61 nmol/L)	42 ng/mL (about 104 nmol/L)

The cats were tested at six and nine months of age.

Every pet tested was below 100 ng/mL (about 250 nmol/L), the level some researchers consider optimal for dogs. That figure comes from a study that found certain health markers levelled off once dogs reached 100–120 ng/mL.⁵ There is no agreed standard yet, and many veterinary labs use lower reference ranges, so these results don't mean every pet is deficient. They do suggest many pets may sit well below the level some researchers consider optimal.

Figure 1: Vitamin D concentrations in dog sera (ng/mL), n=11. The mean concentration was 24.35 ± 5.82 ng/mL. Suggested optimal range: 100–120 ng/mL.⁵

The cats' levels rose between six and nine months of age, but even at nine months the highest was 80 ng/mL. Vitamin D levels naturally climb as kittens mature,¹² and no studies have yet set vitamin D requirements specifically for cats. Most research assumes cats need the same as dogs, so determining cat-specific values will be an important next step.

 

Figure 2: Vitamin D in the blood of Ontario cats (n=10), measured with a commercially available ELISA test. Mean 41.55 ± 18 ng/mL; none reached the suggested optimal range of 100–120 ng/mL.

What Should I Do About My Pet's Vitamin D?

1. Ask your veterinarian about a blood test. It's the only way to know your pet's actual vitamin D level.
2. Check your pet's food. Look at the label or ask the manufacturer how much vitamin D it contains, especially if you feed a homemade diet.
3. Consider a supplement if your vet agrees. If your pet's level is low, vitamin D3 can help fill the gap.

More isn't better. Too much vitamin D can be harmful to pets, pushing calcium to unsafe levels that can damage the kidneys. It's the reason some pet foods have been recalled for excess vitamin D. Always stick to the recommended dose.

Supporting Your Pet with Vitamin D3

When extra vitamin D is appropriate, vitamin D3 (cholecalciferol) is a convenient option.

ImmunoCeutica's Pet D provides 500 IU of vitamin D3 per drop in an MCT oil base, formulated for dogs and cats. The liquid format makes it easy to add to your pet's daily routine. See the Pet D dosing guide for how many drops suit your pet's size.

Always follow the recommended dosage and consult your veterinarian if you have questions about your pet's nutritional needs.

For educational purposes only. Reviewed by Emily Dutka, MSc. 

REFERENCES

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2. Chacar FC, Kogika MM, Zafalon RVA, Brunetto MA. Vitamin D metabolism and its role in mineral and bone disorders in chronic kidney disease in humans, dogs and cats. Metabolites. 2020;10(12):499.
3. Cartwright JA, Gow AG, Milne E, et al. Vitamin D receptor expression in dogs. J Vet Intern Med. 2018;32(2):764–774.
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12. Backus RC, Ueda DC. Age-dependent changes in plasma concentrations of 25-hydroxyvitamin D may complicate vitamin D status assessment of immature cats. Front Vet Sci. 2024;11:1365204.