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Posted On Jun 24, 2025

Updated On Jun 30, 2025

Vitamin D In Dogs With Atopic Dermatitis

Dermatology

Atopic dermatitis is one of the most common skin diseases treated in the veterinary practice setting and treatment can be quite challenging. Compromise of the skin barrier is one factor that can contribute to the development of atopy (allergic dermatitis) in dogs, as this can potentiate the penetration of environmental allergens into the skin. Vitamin D is a hormone that is involved in the epidermal barrier function, modulation of immune responses to allergens, as well as production of antimicrobial peptides (thus influencing bacterial growth on the skin surface).

A study[1] back in 2018 examined the effects of vitamin D supplementation in dogs with atopic dermatitis. The initial purpose was to evaluate the efficacy of cholecalciferol and a vitamin D receptor (VDR) agonist - paricalcitol - in the treatment of canine atopic dermatitis. This placebo-controlled, double-blinded study included a total of 23 client-owned dogs that had a diagnosis of atopic dermatitis and that were pruritic with observable skin lesions. 

After the first 13 dogs were enrolled, the study design was changed because a number of dogs experienced adverse effects associated with the paricalcitol (VDR). Adverse effects of paricalcitol included polyuria, polydypsia and hypercalcemia (which resolved within a day of discontinuing the VDR). So, the study design was amended to only evaluate the effects of cholecalciferol (vitamin D) as compared to placebo (palm oil). There was an 8-week washout period between treatments. 

Blood samples to assess ionized calcium and vitamin D metabolite levels were collected throughout the study and standardized scoring systems were used to evaluate skin lesion severity (canine atopic dermatitis extent and severity index) and pruritus (pruritus visual analogue scale). Any other ongoing treatments that the dogs were receiving for atopic dermatitis (e.g. prednisone) were not changed before or during the study. Therefore, each dog essentially served as its own control because the study treatments would either help or not help to reduce their pruritus and/or skin lesions.

Dogs were administered a starting dose of 300 IU/kg cholecalciferol (vitamin D), and the dose was increased every two weeks based on their ionized calcium concentration and clinical signs. The cholecalciferol dose escalation was from 300 to 700 to 1400 IU/kg. If ionized calcium levels exceeded the upper limit of the reference range, the dose of cholecalciferol was reduced to the previous dose. If ionized calcium levels were within the reference range and symptoms had not improved, the dose was increased. 

No dogs experienced adverse effects from the cholecalciferol and most of the dogs responded well to a dose of 1000-1400 IU/kg. A few dogs required a higher dose and one dog responded well to the lower dose of 300 IU/kg. After 8 weeks of treatment, dogs receiving the cholecalciferol showed significantly less pruritus and significant reductions in lesion severity scores as compared to placebo. At the beginning of the study, most dogs had low or very low serum levels of vitamin D metabolite (25-OH-D3). Over the 8-week study period their serum levels increased approximately 250% and this increase in serum 25-0H0D3 significantly correlated with a reduction in pruritus. There was long term follow-up for two of the dogs in the study - who continued to receive vitamin D orally for a period of six months - and no adverse effects were observed. One of those dogs then discontinued the vitamin D and its clinical signs returned but subsequently improved again when therapy was resumed.

Oral vitamin D significantly decreased itch and skin lesion severity in this study of dogs with active atopic dermatitis. Symptoms of atopy returned during the washout period and when cholecalciferol was discontinued. Results suggest that cholecalciferol can be considered a safe and effective treatment for treating dogs with atopic dermatitis. Serum calcium monitoring is advised, especially if higher doses of vitamin D are administered. It's also important for clinicians to conduct a thorough diet history if considering vitamin D administration. Cod liver oil, liver (organ meat), and certain omega 3 fatty acid supplements are also external sources of vitamin D and could potentiate toxicity. No dog should receive vitamin D supplementation without a veterinarian's supervision, and monitoring is essential because hypercalcemia can lead to serious health concerns including the formation of kidney stones.

[1] Vitamin D shows in vivo efficacy in a placebo-controlled, double-blinded, randomised, clinical trial on canine atopic dermatitis. Vet Record. April 2018:182(14). doi 10.1136/vr.104492