Vitamin D is fat soluble and is made up of a group of steroid-like molecules.
While people can convert vitamin D precursors to the active D form when exposed to ultraviolet light (that's why vitamin D is called the "sunshine vitamin!), regrettably dogs cannot do that effectively. Dogs have to get their vitamin D supplies from food.
Once ingested, vitamin D undergoes chemical changes in the liver and tissues that convert it into an active form, which has anti-inflammatory effect.
Vitamin D from animal sources is converted to its active D3 form (cholecalciferol), whereas vitamin D from plant sources is converted to D2 (ergocalciferol).
If you feed a high-quality commercial diet, chances are your dog is getting sufficient amounts of vitamin D.
If you home cook for your dog, you need to exercise more careful. Too little vitamin D can cause health problems (see below), but too much can cause toxicity since this vitamin is not water soluble and can't be eliminated through urine.
Food sources that are rich in vitamin D include:
Vitamin D regulates the calcium and phosphorus levels in the blood and stimulates the kidney to conserve calcium. It is important for normal bone formation and maintenance. It is also needed for normal muscle and nerve control.
If a growing puppy does not have sufficient vitamin D in the body, he will suffer from rickets.
If an adult dog does not have sufficient supply of vitamin D, he will suffer from softening of the bones (osteomalacia) and osteoporosis.
Also, as mentioned above, since vitamin D has anti-inflammatory effect, it is vital to dogs for the prevention of a variety of chronic diseases, such as IBD, immune-mediated disease, kidney disease, and congestive heart failure.
In addition to the benefits mentioned in the previous section, recent studies have found a link between low levels of vitamin D in dogs and higher risks of certain types of canine cancer.
This is not surprising because vitamin D has anti-inflammatory effect, and cancer is in fact a result of chronic inflammation.
In a 2014 study done by Dr. Selting (professor of Veterinary Oncology, University of Missouri College of Veterinary Medicine) together with several other researchers, lower levels of vitamin D in dogs were found to be associated with higher risks of hemangiosarcoma and splenic cancer.
In another study in 2011, it was found that Labrador retrievers with cutaneous mast cell tumors had much lower levels of vitamin D3 in their blood stream.
Currently studies are underway to determine if vitamin D supplements can prevent mast cell tumors or improve treatment outcome.
In a separate study, it has been found that dogs with lymphoma, carcinoma, histiocytic sarcoma and hemangiosarcoma had significantly lower levels of vitamin D in their blood stream.
But how low is considered "low level" of serum vitamin D3?
Knew you would ask this question!
In the 2014 study mentioned above, Dr. Selting established different vitamin D levels in dogs, ranging from deficiency to toxicity.
The study established that vitamin D sufficiency is obtained when serum vitamin D levels reach 100 to 120 ng/mL. This is the desired level that has optimal health effect on the dog.
At this level, the dog not only does not run the risk of developing rickets or osteoporosis, but also has a lower risk for various chronic diseases, including certain cancer types.
Vitamin D serum levels much higher than the sufficiency level indicate vitamin D toxicity, which by the way is rather rare unless the dog has ingested rodent-killing agent, or has had an overdose of vitamin D supplements.
The study also defined the difference between "deficiency" and "insufficiency".
Vitamin D deficiency results when serum vitamin D levels are way below the 100-120 ng/mL range, so low that the development of rickets cannot be prevented.
Vitamin D insufficiency is a level that is high enough to prevent rickets, but not high enough to help prevent various chronic diseases.
So how do I know if I need to give vitamin D supplements to my dog? You ask.
You don't know until a blood test is done to find out if your dog's serum vitamin D level is sufficient. That is the first step.
Once the current level is found out, you, together with your vet, can decide whether supplementation is necessary and, if so, how much to dose.
This is very important.
Do not start giving your dog vitamin D supplements without a blood test and without consulting with your vet, since nobody knows how much, if any, vitamin D supplementation YOUR dog needs until his current serum vitamin D level is found out.
After starting supplementation (if your dog needs it), the serum levels should be tested again in 1-2 months' time, and every year thereafter to ensure that the levels are at the optimal 100 to 120 ng/mL range.
In the meantime, be sure to feed your dog a healthy, balanced diet. If you home cook for your dog, include foods that are rich in vitamin D.References