Influence of Various Factors on Circulating 25(OH) Vitamin D Concentrations in Dogs with Cancer and Healthy Dogs

Abstract

Background: Low blood 25-hydroxyvitamin D (25(OH)D) concentrations have been associated with cancer in dogs. Little research has examined what other factors may affect 25(OH)D concentrations.

Objectives: (1) To determine whether the presence of cancer (lymphoma, osteosarcoma, or mast cell tumor [MCT]) in dogs is associated with plasma 25(OH)D concentrations and (2) identify other factors related to plasma 25(OH)D concentrations in dogs.

Animals: Dogs newly diagnosed with osteosarcoma (n = 21), lymphoma (n = 27), and MCT (n = 21) presented to a tertiary referral oncology center, and healthy, client-owned dogs (n = 23).

Methods: An observational study design was used. Dietary vitamin D intake, sex, age, body condition score (BCS), muscle condition score (MCS), and plasma concentrations of 25(OH)D, 24,25-dihydroxyvitamin D (24,25(OH)₂ D) (a marker of CYP24A1 activity), as well as ionized calcium (ICa), parathyroid hormone, and parathyroid hormone-related protein concentrations were measured. An analysis of covariance was used to model plasma 25(OH)D concentrations.

Results: Cancer type (P = 0.004), plasma 24,25(OH)₂ D concentrations (P < 0.001), and plasma ICa concentrations (P = 0.047) had significant effects on plasma 25(OH)D concentrations. Effects of age, sex, body weight, BCS, MCS, and plasma PTH concentrations were not identified. A significant interaction between ICa and cancer was found (P = 0.005). Plasma 25(OH)D concentrations increased as ICa concentrations increased in dogs with cancer, whereas plasma 25(OH)D concentrations decreased as ICa concentrations increased in healthy dogs.

Conclusions and clinical importance: Results support a relationship between cancer and altered vitamin D metabolism in dogs, mediated by plasma ICa concentrations. The CYP24A1 activity and plasma ICa should be measured in studies examining plasma 25(OH)D concentrations in dogs.

Keywords: 24,25-dihydroxyvitamin D; 25-hydroxyvitamin D; Lymphoma; Osteosarcoma.

Figure 1

Statistical model of relationship between plasma ICa concentration (mmol/L) and plasma 25(OH)D (ng/mL) concentrations at a plasma 24,25(OH)2D concentration of 24 ng/mL in healthy dogs and those with cancer. RMSE = 0.1036. Healthy n = 23, osteosarcoma (OSA) n = 21, lymphoma (LSA) n = 27, mast cell tumor (MCT) n = 21, 25(OH)D = 25‐hydroxyvitamin D, ICa = ionized calcium.

Figure 2

Statistical model of relationship between plasma 24,25(OH)2D concentration (ng/mL) and plasma 25(OH)D (ng/mL) concentrations at a plasma ICa concentration of 1.33 mmol/L in healthy dogs and those with cancer. RMSE = 0.1036. Healthy n = 23, osteosarcoma (OSA) n = 21, lymphoma (LSA) n = 27, mast cell tumor (MCT) n = 21; 25(OH)D = 25‐hydroxyvitamin D, 24,25(OH)₂D = 24,25‐dihydroxyvitamin D.