Vitamin D and Pet Immune Function: What Pet Owners Should Know This Tick Season

Quick Answer: Dogs and cats cannot synthesize vitamin D from sunlight the way humans can — they rely entirely on diet. Low vitamin D levels in pets are associated with weakened immune function and increased susceptibility to bacterial and viral infections, including tick-borne diseases. Supporting your pet's vitamin D levels is one component of a comprehensive tick season wellness strategy.

Key Takeaways:

• Unlike humans, dogs and cats cannot produce vitamin D through sun exposure and depend entirely on dietary sources
• Vitamin D receptors are found on immune cells throughout the body - vitamin D helps regulate and activate the immune response
• Studies show approximately 75–85% of dogs may have insufficient vitamin D levels
• Low vitamin D in pets is associated with immune-mediated disease and higher infection risk
• Tick protection requires three layers: prevention, early detection, and immune support

As tick season approaches across Canada, many pet owners are thinking about protection strategies for their dogs and cats. While tick prevention is multifaceted – involving topical treatments, environmental management, and regular vet checks are just a few of the many ways of tick prevention and management – one often-overlooked factor is your pet's overall immune function.

What does vitamin D do for your pet's immune system?

You might know vitamin D most famously for its role in bone health – but did you know it also plays a key role in immune function?

Vitamin D receptors are found on cells throughout the body, including leukocytes (white blood cells). When vitamin D (25-hydroxyvitamin D (25[OH]D)) binds to these receptors, it helps regulate immune responses by activating certain immune cells that are critical for recognizing and fighting pathogens – supporting your pet's ability to respond to threats while maintaining balance in the immune system ^1,2.

Tick-borne diseases such as Lyme disease in dogs, and Cytauxzoonosis in cats, are caused by the transmission of bacteria and parasites, and can lead to lethargy, loss of appetite, and fevers³. In both cats and dogs, low vitamin D concentrations have been seen to be associated with immune-mediated diseases and overall, an increased risk for bacterial and viral infection^4,5.

Why can't pets get vitamin D from sunlight?

Unlike humans, dogs and cats cannot synthesize sufficient amounts of vitamin D through sunlight exposure. They rely entirely on dietary sources - which means deficiency is common and easy to miss, particularly in indoor pets or those on nutritionally incomplete diets.

In 2017, a study done on 320 dogs revealed that approximately 75-85% of the cohorts were Vitamin D insufficient, meaning that their levels were below 100 ng/mL⁶. Aside from diet and supplementation, other factors that may affect your dog’s vitamin D level include breed, sex, and intact status (having been spayed or neutered). 

Vitamin D deficiency is widespread, affecting both humans and animals across demographics.

The Three Layers of Tick Protection for Pets

Protecting your pet from tick-borne diseases requires a comprehensive approach:

Layer 1: Prevention

• Use veterinarian-recommended tick preventatives
• Check your pet after outdoor activities
• Keep grass trimmed and reduce tick habitats in your yard

Layer 2: Early Detection

• Regularly examine your pet for ticks, especially after walks
• Know the signs of tick-borne illness (lethargy, fever, loss of appetite)
• Maintain regular veterinary checkups

Layer 3: Immune Support

• Ensure your pet receives complete, balanced nutrition
• Consider vitamin D supplementation, especially for indoor pets
• Discuss your pet's immune health with your veterinarian

It's important to understand that whether a pet develops tick-borne disease depends on many factors - tick exposure, the specific pathogen, individual immune response, and overall health status. Vitamin D supplementation alone cannot prevent tick-borne diseases, but supporting immune function is a meaningful part of a holistic wellness approach.

How does Pet D support your pet's immunity?

Pet D provides research-backed vitamin D supplementation formulated by immunologists who study immune system regulation at the molecular level. It's designed as a supplementary addition to your pet's food or treats - part of a comprehensive approach to pet wellness, not a replacement for veterinary care or proven tick prevention methods.

With spring approaching, now is a good time to get ahead of tick season - not just with preventatives, but by ensuring your pet's immune system has the nutritional foundation it needs.

Questions to Ask Your Veterinarian

As we head into tick season, consider discussing these questions with your vet:

1. Is my pet at higher risk for tick exposure based on our location and lifestyle?
2. What tick prevention strategy do you recommend for my specific pet?
3. Should I be concerned about my pet's vitamin D levels?
4. Are there signs I should watch for that might indicate immune system concerns?

Our Approach

As immunologists, we created Pet D because we understand immune system regulation at the molecular level. Our background in immunological research gives us a unique insight into what pets need for optimal immune function.

Pet D provides research-backed vitamin D supplementation formulated by scientists who study immune systems for a living. It's part of a comprehensive approach to pet wellness, not a replacement for veterinary care or proven tick prevention methods.

This tick season, focus on all three layers of protection: prevention, detection, and supporting your pet's overall health. Your veterinarian is your best partner in creating a tick protection plan tailored to your pet's specific needs.

References 

1. Mehrani, Y., Morovati, S., Tieu, S., Karimi, N., Javadi, H., Vanderkamp, S., Sarmadi, S., Tajik, T., Kakish, J. E., Bridle, B. W., & Karimi, K. (2023). Vitamin D Influences the Activity of Mast Cells in Allergic Manifestations and Potentiates Their Effector Functions against Pathogens. Cells, 12(18), 2271. https://doi.org/10.3390/cells12182271
2. Parravicini, V., & Caserta, S. (2010). The Immunomodulatory Roles of Vitamin D: New Tricks for an Old Dog. Molecular Interventions. 10(4), 204-208. https://doi.org/10.1124/mi.10.4.3
3. Ontario Veterinary College Health Sciences Centre. (2025). Tick-borne illness in dogs and cats: What pet owners need to know. https://www.ovchsc.ca/news/tick-borne-illness-in-dogs-and-cats-what-pet-owners-need-to-know
4. Mick, P.J, Peng, S.A., & Loftus, J.P. (2019). Serum Vitamin D Metabolites and CXCL10 Concentrations Associated With Survival in Dogs With Immune Mediated Disease. Front. Vet. Sci. 6,247.  https://doi.org/10.3389/fvets.2019.00247
5. Corbee, R.J. (2020). Vitamin D in Health and Disease in Dogs and Cats. Advances in Small Animal Care. 1,265-277. https://doi.org/10.1016/j.yasa.2020.07.017
6. Sharp, C. R., Selting, K. A., & Ringold, R. (2015). The effect of diet on serum 25-hydroxyvitamin D concentrations in dogs. BMC research notes, 8, 442. https://doi.org/10.1186/s13104-015-1360-0

 

Reviewed by Nancy Gao, M.Sc., Animal Biosciences