Many people take vitamin D supplements nowadays, and for good reason. Research has found that low levels of this vitamin are associated with a variety of serious health issues, including cardiovascular disease and hypertension, cancer, diabetes, multiple sclerosis, asthma, infectious diseases, rickets and other problems.

More recently, researchers have uncovered similar findings in dogs and cats. Most of the studies involve dogs, but the findings are applicable to cats as well. Congestive heart failure, neoplasia, renal and infectious diseases, IBD, feline oral resorptive lesions (FORL), rickets and other conditions are all connected to a deficiency of vitamin D in these animals.

D in detail

• Vitamin D is made up of a group of steroid-like molecules. It’s similar in structure to other steroid hormones like testosterone, aldosterone, estradiol, progesterone and cortisone.

• In order for it to be effective, it needs to bind to a receptor. Vitamin D is like a key that fits perfectly into a lock – the membrane receptor. Once the two are “mated”, the vitamin D can have a positive effect on the body. In humans, vitamin D receptors have been found in a wide variety of tissues, and is also believed to regulate over 2,000 genes.

• Once it is ingested orally, vitamin D undergoes chemical changes in the liver and tissues that convert it to an “activated” form. It has an anti-inflammatory effect in tissues where it is active. Chronic inflammation underlies many conditions, including neoplasia and immune-mediated disease. However, studies have shown that serum levels of vitamin D high enough to prevent rickets are still insufficient for maintaining cellular health and dampening inflammatory processes. As a result, many professionals in the medical community are suggesting that people and animals be supplemented with oral vitamin D.

• Vitamin D regulates the absorption of calcium and phosphorus from the bowel, and is involved with calcium mobilization from bone. When derived from animal sources, it is termed cholecalciferol and converts to vitamin D3. Ergocalciferol is the plant-sourced form, and converts to vitamin D2. Most species are able to utilize both forms, although in cats, it has been found that cholecalciferol (D3) maintains vitamin D status with greater efficiency than ergocalciferol (D2). Vitamin D2 does not prevent or reverse rickets, as compared to vitamin D3.

• Dogs and cats, unlike humans and most other species, are unable to naturally convert very much vitamin D in their skin when exposed to ultraviolet light. Pro-vitamin D3 (7-dehydrocholesterol) in the skin of dogs and cats has a much lower concentration than that found in the skin of species that can convert 7-dehydrocholesterol to cholecalciferol. For this reason, dogs and cats differ from people and other animals in that they derive all their vitamin D from food, and none from sunlight.

Normal Ranges of D3

In a landmark study involving 282 German shepherds and golden retrievers, Dr. Kim Selting, a professor of Veterinary Oncology at the University of Missouri College of Veterinary Medicine, and additional researchers at three other veterinary colleges, established optimal ranges for vitamin D3 in dogs. The study established that vitamin D sufficiency is obtained when blood levels reach 100 to 120 ng/mL; it also helped further define vitamin D3 deficiency and insufficiency.

• Deficiency is defined as a serum level of vitamin D3 that isn’t high enough to prevent rickets.

• Insufficiency is defined as a level high enough to prevent the development of rickets, but too low to help prevent a variety of chronic disease conditions.

• Sufficiency is defined as the serum level of vitamin D3 that has an optimal effect on health. Studies have shown a lower risk for a variety of chronic diseases when vitamin D3 levels are sufficient.

• Toxicity results from serum levels much higher than sufficiency, and commonly results in hypercalcemia. Rodenticides often use a synthetic vitamin D that causes excessive amounts of calcium to be released into the blood from the bones, leading to a heart attack from the hypercalcemia.

Vitamin D and cancer in dogs

Several studies have measured the relationship between serum vitamin D concentrations and the incidence of certain types of cancer. Oral supplementation with vitamin D that’s sufficient to create healthy serum levels may be a credible strategy in the prevention of some cancers.

1. One interesting finding from Dr. Selting’s study is that neutered male dogs have, on average, lower serum vitamin D concentrations. Neutered male dogs also have an increased prevalence of cancer, as well as knee injuries. Given the relationship between vitamin D and bone development, there may be an as yet undiscovered link between insufficient levels of vitamin D and cruciate ligament disease.

2. Dr. Selting’s study also measured serum concentrations in 62 dogs presenting with blood in their abdominal cavities as a result of various cancers such as hemangiosarcoma and splenic malignancies, and compared them to 282 dogs without cancer. Lower levels of vitamin D were found to be associated with a higher risk of cancers of the spleen.

3. A separate 2011 study found that 33 Labrador retrievers with cutaneous mast cell tumors had significantly lower serum concentrations of vitamin D3 than 54 unaffected controls. It is unknown if supplementing with vitamin D3 could prevent mast cell tumors or improve treatment outcomes, but studies evaluating that possibility are underway.

4. In yet another study, the “D”  levels in dogs with cancer were found to be significantly lower than those in dogs without the disease. The cancer types looked at by the study included:

• Carcinoma

• Histiocytic sarcoma

• Hemangiosarcoma

• Lymphoma

• Sarcoma

This evidence strongly supports the value of having your dog or cat’s vitamin D levels measured, and of providing him with a supplement of vitamin D3 if his levels are insufficient. Start by taking him to the veterinarian for an initial blood sample to measure his baseline levels. Based on these test results, vitamin D can then be supplemented orally for one to two months. At this point, his serum levels should be re-tested, and annual tests done thereafter to ensure they remain at sufficiently healthy levels (100 to 120 ng/ml).

Though it’s known as the “sunshine vitamin”, it’s important to remember that your dog or cat can’t get vitamin D from spending time outdoors. Given its many health benefits, it’s more than worth your while to get to know this nutrient better, have your companion’s levels checked on a regular basis, and consider supplementation.

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