Vitamin D is one of the few nutrients where both deficiency and excess can create health concerns. Unlike people, dogs and cats do not effectively produce meaningful amounts of Vitamin D from sunlight. Their levels depend almost entirely on diet, digestion, absorption, and how the body processes nutrients.
At Balanced Pet NW, Vitamin D testing has become an important part of evaluating many chronic and complex cases. Levels are often far less predictable than most people expect. Two dogs living in the same household, eating the same food, and sharing the same lifestyle may still have very different Vitamin D levels. Vitamin D functions more like a hormone than a simple vitamin, and receptors for Vitamin D are found throughout the body, including on immune cells, which means it influences far more than bone health alone.
Low Vitamin D levels may affect:
- Immune regulation
- Inflammatory balance
- Skin and allergy conditions
- Digestive health
- Joint comfort
- Thyroid function
- Recovery from chronic illness
- Cancer support and immune surveillance
In some patients, unresolved inflammation or recurring flare-ups may partly relate to underlying nutrient imbalances that have not yet been identified. Vitamin D is fat-soluble, meaning the body stores excess amounts over time. Because of this, supplementation should never follow a one-size-fits-all approach. Too little may leave deficiencies unresolved, while too much can lead to toxicity. Excess Vitamin D can contribute to lethargy, kidney damage, metabolic dysfunction, and calcium imbalances, among other concerns. For that reason, testing is far safer and more useful than relying on generalized supplementation. At our clinic, we use Vitamin D testing to develop individualized recommendations based on the patient’s needs, diet, health status, and laboratory results.
We perform Vitamin D testing through VDI Laboratory using a blood sample collected after an 8- to 12- hour fast. Because fasting is required, these appointments are typically scheduled in the morning so pets can eat breakfast afterward. The specific marker measured is serum 25(OH)D, which is considered the most reliable indicator of Vitamin D status. Additional nutritional testing may also be recommended in some cases, including Vitamin B12, magnesium, and omega-3 fatty acid levels.
Foods naturally containing Vitamin D include liver, sardines, salmon, egg yolks, and UV-exposed culinary mushrooms. Commercial diets are supplemented with Vitamin D as well, though individual absorption and metabolism still vary considerably between pets.
Vitamin D is not the answer to every chronic condition, but it can still be an important factor in patient health. Since deficiency can affect immune and inflammatory pathways throughout the body, identifying low levels may help explain why some patients struggle to fully stabilize despite otherwise appropriate treatment plans. Testing provides information that can help inform a more precise and individualized approach to care, especially in patients with digestive disease, chronic inflammation, immune-related conditions, or cancer support needs.
