What is Vitamin D?
Vitamin D is a fat-soluble vitamin necessary for the proper absorption of calcium and phosphorous in the body. Diet is the primary source of vitamin D in the form of 25 hydroxyvitamin D (25vitD) for dogs and cats; it is acquired from the protein source in the food. Unlike humans, our pets do not make vitamin D3 in their skin with exposure to sunlight in quantities sufficient to provide their bodily needs. Vitamin D3 is supplied in highest quantities in fish and egg yolks. Most commercial diets have vitamin D3 added, as the vitamin D3 in food is easily destroyed with processing.
All pets should be tested to determine their vitamin D levels at least once per year. VDI labs has shown that optimal levels are 100 to 150 ng/ml on blood testing. Pets with levels below 40 ng/ml are much more likely to suffer from a variety of diseases.
Diseases Associated with Low Vitamin D
- Cancer - It has been reported that dogs and cats with lymphoma, mast cell tumors, hemangiosarcoma, carcinoma, histiocytic sarcoma, and other cancers all have 25vitaminD values below 40 ng/mL. The relative risk of having cancer increases to almost 4x when 25vitaminD values are below 40 ng/mL.
- Chronic Intestinal Disease - Disease severity and the incidence of chronic enteropathy (CE) in both cats and dogs increases substantially when 25vitD values fall below 40 ng/mL. In CE, survivors vs non-survivors can be separated when 25vitD values fall below 30ng/mL.
- Heart disease - Congestive heart failure is more prevalent in dogs with 25vitD values below 40ng/mL. Heart remodeling in chronic valvular heart disease worsens as 25vitD values fall below 30 ng/mL.
- Atopic dermatitis - Vitamin D receptors are found on cells associated with the immune response including white blood cells, mast cells, skin, and intestinal cells. Studies found that inflammation and itching drops when the 25vitD levels in the blood reach 100 ng/ml.
- Kidney disease - Low vitamin D is found in all kidney disease patients. Studies show acute and chronic kidney disease is more prevalent in dogs with 25vitD values below 40 ng/mL. As 25vitD values fall below 40ng/mL, creatinine increases dramatically.
- Hyperparathyroidism - Vitamin D is associated with calcium and phosphorous absorption and utilization in the body. Tumors in the parathyroid gland cause low vitamin D.
- Immune mediated disease - IMHA (Immune Mediated Hemolytic Anemia), ITP (Immune Mediated Thrombocytopenia), and IMPA (Immune Mediate Polyarthropathy) are immune mediated diseases for which low store of 25vitD has been associated. All dogs in the study had insufficient (40 -100 ng/mL) or deficient (<40 ng/ml) 25vitD levels, supporting the role of vitamin D in the innate immune process.
- Infection - Dogs with respiratory diseases had a significantly lower 25vitD level than control dogs. Dogs positive for canine herpesvirus had a significantly lower 25vitD level than those testing negative. This study supports the relationships between vitamin D and acute respiratory infections as seen in human studies.
- Pancreatitis - Dogs with acute pancreatitis have significantly lower 25vitD levels than healthy dogs.
- Feline tooth resorption - Although causes have not been determined for tooth resorption in cats in general, one study suggests that cats with tooth resorption have significantly higher serum concentrations of 25-hydroxyvitamin D than cats do without tooth resorption. These researchers also found that 41 percent of canned cat foods have in excess of 30 times the vitamin D requirements of cats.
- Hospital Mortality - Hospitalized cats with 25vitD levels below 40 ng/mL have an 8x higher incidence of dying and hospitalized dogs with 25vitD levels below 33ng/mL have a 7x higher incidence of dying.
- Gallbladder Mucocele - Gallbladder mucocele is a common biliary disorder in dogs. Vitamin D deficiency is one of many potential causes of gallbladder hypokinesia in humans and supplementation results in complete resolution of stasis. Dogs with Gallbladder Mucocele had a significantly lower 25vitD level than healthy controls, similar to findings in human literature.
Factors That Affect Vitamin D levels in dogs and cats include:
- Food - Commercial diets can have profound differences in vitamin D levels.
- Age - As animals get older their ability to absorb vitamin D diminishes.
- Neuter Status - Male neutered dogs have 27% less 25vitD than intact males; spayed females have 9% less 25vitD than intact females.
- Diseases affecting the GI tract lead to decreased absorption of vitamin D.
- Medications - NSAIDs can cause decreases of up to 50%.
Many Pets Have Low Vitamin D
- Testing shows 25vitD deficiency of less than 40 ng/ml in 11% of dogs and 22% of cats.
- Only 21% of dogs and 14% of cats tested showed sufficient 25vitD levels over 100 ng/ml.
Vitamin D Testing Made Easy
Vitamin D insufficiency is easy to test and correct. The amount of D3 required depends upon the degree of insufficiency (determined by testing), the patient’s species, weight, age, intact status, diet, and other factors. Testing is simple and cost effective using the VDI test. A blood sample from the patient is applied to a card and simply mailed by common carrier. The card easily crosses international borders without custom declarations. Dosing information is provided on the report with a pet-parent friendly information sheet detailing the result and D3 dosing required for the cat or dog.
Vitamin D3 supplementation is typically required for life and typically increases with age; annual 25vitD testing is recommended. In a normal healthy dog or cat, it takes 8-10 weeks for equilibrium to establish. Vitamin D levels will need to be re-evaluated when there are changes in diet and/or D3 supplementation.