Vitamin D status is seasonally stable in northern European dogs

Vet Clin Pathol. 2020 Jun;49(2):279-291. doi: 10.1111/vcp.12859. Epub 2020 May 20.


Background: Numerous studies in veterinary species have recently linked vitamin D status with nonskeletal health disorders. Previous studies have indicated that dogs cannot produce endogenous vitamin D via cutaneous production and rely solely on dietary intake of vitamin D. The seasonal variation of vitamin D seen in humans due to changes in ultraviolet (UV) exposure, therefore, is unlikely to be replicated in these animals.

Objectives: The objective of this study was to investigate the natural variation in 25-hydroxyvitamin-D concentrations in dogs subject to seasonal UV exposure.

Methods: This longitudinal study followed 18 healthy dogs fed a standardized diet over 1 year, with blood samples obtained monthly. Two key vitamin D metabolites, 25-hydroxyvitamin-D2 and 25-hydroxyvitamin-D3 , were assessed by liquid chromatography-tandem mass spectrometry in serum samples. Various other biochemical parameters were also measured. Seasonality was assessed using cosinor statistical analysis.

Results: Although the dogs were subject to seasonally varying UV radiation, 25-hydroxyvitamin-D and related biomarkers (including calcium and parathyroid hormone) remained stable over time and did not follow a seasonal pattern. 25-hydroxyvitamin-D was not positively correlated with exposure to UV radiation. Nonetheless, variation in 25-hydroxyvitamin-D concentrations between individual dogs was detected.

Conclusions: Given the standardization of diet, we concluded that the seasonal stability of 25-hydroxyvitamin-D concentration (vitamin D status) was likely a direct result of lack of cutaneous vitamin D production in this species and highlights the importance of dietary intake. The variation in 25-hydroxyvitamin-D concentration between animals warrants further investigation.

Keywords: 25-hydroxyvitamin-D; LC-MS; season; ultraviolet B.

MeSH terms

  • 25-Hydroxyvitamin D 2 / blood
  • 25-Hydroxyvitamin D 2 / radiation effects
  • Animals
  • Calcifediol / blood
  • Calcifediol / radiation effects
  • Calcium / blood*
  • Calcium / radiation effects
  • Chromatography, Liquid / veterinary
  • Dogs
  • Female
  • Longitudinal Studies
  • Male
  • Parathyroid Hormone / blood*
  • Parathyroid Hormone / radiation effects
  • Reference Values
  • Seasons
  • Ultraviolet Rays
  • Vitamin D / analogs & derivatives*
  • Vitamin D / blood
  • Vitamin D / radiation effects


  • Parathyroid Hormone
  • Vitamin D
  • 25-Hydroxyvitamin D 2
  • 25-hydroxyvitamin D
  • Calcifediol
  • Calcium