This week's Evidence Based Update is a continuation of the discussion on the impact of vitamin D on dog health. In this segment we discuss suggested serum vitamin D levels for maintenance of health and findings of a study that examined serum vitamin D levels in dogs with cancer.
The role of vitamin D in calcium metabolism and the preservation of cellular health is well established in human studies. Reports from recent studies also indicate that many tissues can convert 25-hydroxyvitamin D [25(OH)D] without calcium. Vitamin D is present in a diverse array of cells, tissues, and organs, such as cardiac cells, immune cells, vascular smooth muscle, colon, brain, breast, brain, and bone. Hence, an insufficient level of vitamin D is associated with cardiovascular disease, hypertension, diabetes, cancer, infectious disease, asthma, and skeletal disease, among other disorders.
Notably, the vitamin D receptor has been identified as a factor in the regulation of well over 2000 genes. Moreover, numerous studies have linked gene regulation by vitamin D with an anti-inflammatory effect, which further links its insufficiency with various diseases caused by chronic inflammation.
Low serum concentration of 25(OH)D is associated with serum levels of certain biomarkers in humans. For example, there is an inverse relationship between intact parathyroid hormone (iPTH) and vitamin D—as 25(OH)D serum blood concentration increases, iPTH decreases, and the point at which iPTH levels plateau indicates the optimum concentration of 25(OH)D in humans. No such studies have been done to define the optimum levels of 25(OH)D in dogs; the determination of which is of great importance because virtually the only source of vitamin D for dogs is dietary. Previous canine studies have reported that dogs with insufficient vitamin D are at risk for cardiac and inflammatory bowel disease as well as cancer, and they remain at risk for these diseases for up to 12 months follow-up.
Selting and colleagues recently reported on the first analysis in healthy dogs (n=282) and dogs with hemoabdomen and splenic mass (n=62) to determine optimal serum concentrations of 25(OH)D using 4 biomarkers (iPTH, canine C-reactive protein [c-CRP], calcium, and phosphorous). They also evaluated 25(OH)D as a risk factor for cancer.
Serum 25(OH)D concentrations varied widely among the study dogs owing to dietary vitamin D content. As in humans, the investigators found an inverse relationship between iPTH and 25(OH)D in healthy dogs—specifically, iPTH plateaued at about 8 pg/mL-1 when 25(OH)D concentration reached 100 ng/mL-1
Calcium and potassium were affected by concentrations of iPTH and 25(OH)D. Total serum calcium and absolute serum phosphorous concentrations were not affected by increases in serum 25(OH)D; however, phosphorous levels changed across 25(OH)D concentrations and plateaued at ≥80 ng/mL-1 Mean c-CRP concentrations decreased at 25(OH)D concentrations above 100 ng/mL-1 .
In this week's Evidence Based Update we reveal what the study showed regarding 25(OH)D concentrations and the correlation with cancer risk, suggested 25(OH)D levels for maintenance of health, levels suggestive of toxicity, and considerations around treatment and precautions when administering vitamin D supplementation.
View this Evidence Based Update (Running time 10 mins)
Reference
Selting KA, Sharp CR, Ringold R, Thamm DH, Backus R. Serum 25-hydroxyvitamin D concentrations in dogs - correlation with health and cancer risk. Vet Comp Oncol. 2014 Jul 8. doi: 10.1111/vco.12101. [Epub ahead of print]
