Effects of Short-Term Calcifediol Supplementation on Leukocyte Cytokine Production in Healthy Dogs: A Randomized, Double-Blinded, Placebo-Controlled Crossover Trial.

Vitamin D modulates the immune response in many species, including dogs. To date, research investigating the immunological effects of vitamin D in dogs is limited to in vitro studies. Provide PO calcifediol supplementation to healthy dogs to evaluate its tolerability and assess its effect on leukocyte production of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-10. Eleven healthy client-owned dogs with serum 25-hydroxyvitamin-D3 (25(OH)D3) concentrations ≤ 30 ng/mL. Prospective, randomized, double-blinded, placebo-controlled crossover study. Dogs were randomized to receive calcifediol at 2.3 μg/kg0.75 (low-dose), 4.6 μg/kg0.75 (high-dose), or placebo for 7 days and crossed over to a different treatment arm after 28-day washout periods. Serum 25(OH)D3 was measured using a modified high-performance liquid chromatography method. Whole blood cultures were performed by incubating blood with lipopolysaccharide (LPS), lipoteichoic acid (LTA), or phosphate-buffered saline (PBS) for 24 h, and TNF-α, IL-6, and IL-10 were measured in supernatant using a canine-specific multiplex assay. Both low-dose (median, interquartile range [IQR]; 62 ng/mL, 59-82) and high-dose (93 ng/mL, 80-113) PO calcifediol supplementation increased serum 25(OH)D3 concentrations from baseline (22.2 ng/mL, 20.3-29.3; both p < 0.0001). Low-dose and high-dose calcifediol supplementation decreased LPS-stimulated IL-6 by 197 pg/mL (95% confidence interval [CI]: -369.0 to -24.0; p = 0.03) and 182 pg/mL (95% CI: -355.0 to -8.0; p = 0.04), respectively. Then LPS-stimulated IL-6 concentrations decreased by 2 pg/mL for every 1 ng/mL increase in serum 25(OH)D3 concentration (95% CI: -3.0 to -0.1; p = 0.03). Calcifediol supplementation for 7 days was well-tolerated and decreased LPS-stimulated IL-6 concentrations. Oral calcifediol supplementation may have anti-inflammatory effects in dogs.