This week's Evidence Based Update is a discussion of the role that vitamin D plays in the maintenance of health. It includes a brief review of what we've long known, as well as newer information we've recently learned that could impact the management of patients with a variety of medical problems including chronic GI disorders.
Weight loss, vomiting, and diarrhea over the course several weeks with no obvious cause can indicate possible chronic enteropathy (CE). Several factors can contribute to chronic CE in dogs, including epithelial barrier dysfunction, abnormalities in mucosal immunity, and altered intestinal microbial flora (which will be covered in greater detail in an upcoming Evidence Based Update). Genetics and environmental factors can also contribute, but are not covered in this summary.
It has been reported that serum concentrations of the vitamin D metabolite 25 hydroxyvitamin D [25(OH)D] are lower in dogs with CE than in healthy dogs or dogs without GI disease. A similar correlation of vitamin D deficiency with IBD is well documented in humans, and measurement of serum 25(OH)D is a valuable prognostic tool.
Albumin concentration and hypovitaminosis D. The cause of vitamin D deficiency (hypovitaminosis D) in dogs with CE is unknown. Dogs cannot produce vitamin D through dermal synthesis so insufficient intake through diet is likely an important factor. It's important to note that circulating 25(OH)D binds to vitamin D–binding protein and albumin, and loss of albumin in the intestines is common in dogs with CE. This loss of protein-bound vitamin D may be related to the low levels of vitamin D in dogs with CE; however, further studies on the relationship of vitamin D malabsorption and hypovitaminosis D in dogs are needed.
Hypovitaminosis D: inflammation and immune response. Studies in rodents have shown a connection between vitamin D insufficiency and the onset of intestinal inflammation as well as supplementation and the alleviation of intestinal inflammation. In addition vitamin D receptors, found on many immune cell types, promote vitamin D modulation of the immune responses as well as proinflammatory responses.
Hypovitaminosis D: effect on intestinal flora. Vitamin D is thought to be an important factor in regulating immune response and maintaining naturally occurring, beneficial gut bacteria. And, it has been observed that many dogs with CE have a decreased ability to tolerate and regulate normal intestinal flora. There is evidence in humans and dogs that vitamin D deficiency is linked to disruption of intestinal mucosal barrier function and increased permeability, both of which can contribute to CE.
Unlike in humans with IBD, the prognostic value of serum concentrations of 25(OH)D in dogs with CE has not been sufficiently explored. In a recently published retrospective review, Titmarsh and colleagues examined the relationship between serum 25(OH)D levels at diagnosis and clinical outcome in dogs with CE. In this week's Evidence Based Update we discuss these findings and the possible clinical relevance including:
View this Evidence Based Update (Running time 22 mins)
I reached out to our colleagues at Diamondback Drugs regarding vitamin D supplementation, as Dr. Zenger had mentioned calcitriol might be the drug of choice to consider (and the need to have it compounded for veterinary patients).
They did some research and provided some background information regarding vitamin D:
VITAMIN D3: RECOMMENDED DOSAGES
The Association of American Feed Control Officials (AAFCO) recommends dietary vitamin D of 500 IU/kg of food.
*Dosage is based on the amount of food the dog eats, NOT the dog’s weight.
Dog's Weight Daily Food Consumption Total IU's Daily
< 30 lbs (small) 8 oz. to 12 oz. 100-200 IU
30 - 70 lbs (medium) 1 - 1.5 lbs 300 IU
> 75 lbs (large) 1.5 - 2 lbs 400 IU
AVAILABLE AGENTS ON THE MARKET
Calcitriol is a useful adjunctive drug for treating certain neoplasias as it potentiates some chemotherapy agents. Common brand names include Rocaltrol, Calcijex, and Active Vitamin D3.
FOODS WITH ADEQUATE LEVELS OF VITAMIN D
Foods with adequate levels of vitamin D include: Canned salmon, canned mackerel, canned sardines, fortified dairy products (yogurt or goat milk), beef, liver, and egg yolk. Salmon oil supplementation is known for its high concentration of vitamin D, whereas the effect of fortified dog biscuits is far less, and surprisingly, fish oil supplementation had no effect.
VITAMIN D TOXICITY
While the benefits of adequate dietary vitamin D are well established in dogs, the potential deleterious effects of over supplementation of vitamin D should be acknowledged. Adequate vitamin D supplementation is crucial and excessive amounts may lead to hypercalcemia and pets may present with polydipsia, polyuria, and anorexia. Overdose can cause hypercalcemia, hypercalciuria, and hyperphosphatemia. Acute ingestions should be managed using protocols for removal or prevention of the drug (vitamin D supplement) being absorbed by the GI tract. Orally administered mineral oil may reduce absorption and enhance fecal elimination.
See Related - Part II on this topic : Vitamin D in Canine Health and Cancer Risk
