Canine atopic dermatitis (CAD) is an inflammatory, pruritic, and hereditary skin condition, primarily T-cell mediated. Its management involves a multimodal approach given its multifactorial nature and incurability. A better understanding of the interactions between genetic, environmental, and nutritional factors is crucial for optimizing treatments.
The objective of this review was to synthesize available data on the role of diet, nutrition, and supplements in the management of CAD over the last ten years (2014-2024), highlighting the methodological limitations of existing studies.
The Role of Diet in Canine Atopic Dermatitis
CAD is characterized by increased sensitivity to food and environmental allergens. In dogs allergic to a food ingredient, avoidance of that ingredient is paramount. However, even in the absence of a specific allergy, specialized diets can provide benefits. The gut and skin share important functional and immunological similarities. Gut dysbiosis could lead to intestinal inflammation that exacerbates CAD, or conversely, the abnormal immune reaction of CAD could induce gut dysbiosis. In both cases, specific diets reducing intestinal inflammation, controlling chronic gastrointestinal symptoms, improving gut dysbiosis, and avoiding food allergens have shown improvement in skin symptoms.
Gastrointestinal inflammation, frequently associated with CAD, manifests as symptoms such as diarrhea, vomiting, borborygmi, and flatulence. Dietary changes are effective in managing these symptoms. In allergic dogs that develop skin symptoms (adverse food cutaneous reactions), diet is of paramount importance. Approximately one-third of dogs with CAD have food allergies. Elimination diets, lasting a minimum of 8 weeks, are the gold standard for diagnosis. The most commonly reported food allergens are beef, dairy products, chicken, wheat, and lamb. Allergen elimination is essential. However, cross-contamination in commercial foods often makes it necessary to use prescription diets, or ideally, homemade diets, although these are more complex to balance. Diets based on hydrolyzed proteins (soy, poultry feathers) have been shown to be useful for diagnosing and managing food allergies. Purified amino acid diets with low allergenic carbohydrates are also available and of clinical interest.
It should be noted that improvements have been observed in atopic dogs without gastrointestinal symptoms or specific food allergies, treated with specialized diets. Several studies have shown the benefits of diets enriched with ingredients targeting skin health.
Specialized Diets
Studies have evaluated the efficacy of diets enriched with ingredients known for their beneficial skin properties. A double-blind, placebo-controlled study demonstrated significant improvement in pruritus score and reduced medication requirements in non-allergic dogs fed a diet containing turmeric, licorice root, lutein, and high levels of vitamin E, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Another study observed a significantly lower incidence of pruritus and anti-mite IgE in puppies from bitches fed a diet enriched with ingredients known to support the skin barrier. In a randomized, double-blind, placebo-controlled study, a diet supplemented with polyunsaturated fatty acids, polyphenols, and antioxidants resulted in a significant improvement in CAD severity and extent scores.
The Role of the Gut Microbiome in Canine Atopic Dermatitis: Supplements and Diet
A healthy gut microbiome contributes to immunological tolerance. Atopic dogs have a different microbiome than healthy dogs. Although there is evidence suggesting beneficial effects of probiotics in humans, data regarding their use in atopic dogs remain limited. While improvement in the gut microbiome is correlated with decreased intestinal inflammation and improved skin symptoms, it remains to be determined whether this improvement is a cause or a consequence. Improvement in intestinal inflammation appears to be correlated with improvement in skin symptoms. It seems likely that diet, rather than probiotics alone, is more beneficial for maintaining a healthy gut microbiome. Studies have shown improvements in gut microbiota and clinical signs of CAD after administration of a hydrolyzed fish and rice starch diet or following the combination of a hydrolyzed diet and tyndallized Lactobacillus bacteria.
Raw Food Diets
Currently, there is no conclusive evidence that raw diets offer an advantage over cooked diets. It is possible that they promote a healthier gut microbiome, although without a noticeable effect on systemic markers of inflammation. An association has been noted between raw feeding and the prevention of CAD in West Highland White Terriers, but this study had significant methodological limitations (data from owner observation). Diet modifies gene expression in the skin. In bull terriers, a raw diet altered the expression of genes involved in angiogenesis, as well as lipid and keratinocyte metabolism; however, the clinical impact remains to be clarified.
The Role of Nutritional Supplements in Canine Atopic Dermatitis
Essential Fatty Acids
Omega-3 and omega-6 fatty acids are essential. EPA, an omega-3 found in fish oils, interferes with arachidonic acid and modifies eicosanoid production, theoretically decreasing inflammatory mediators and altering the epidermal lipid barrier. Despite numerous studies, additional clinical benefits of essential fatty acid intake for the treatment of CAD are limited. However, these supplements seem to have a sparing effect on certain medications (prednisolone, cyclosporine, oclacitinib). Studies have shown a reduction in the dose of these medications associated with omega-3 fatty acid supplementation.
Vitamin E
Vitamin E plays a role in the immune system and has antioxidant properties. Studies have demonstrated a significant improvement in CAD severity scores following vitamin E supplementation.
Vitamin D
Vitamin D is important for a healthy immune system. A placebo-controlled study demonstrated a significant decrease in pruritus and skin lesions in dogs receiving cholecalciferol. Careful monitoring of calcemia is necessary due to the risk of toxicity.
Zinc
A cross-over controlled study did not show significant improvement in pruritus, but a decrease in the skin lesion score in a proportion of dogs supplemented with zinc. The number of animals included and confounding factors limit the interpretation of these results.
Non-Nutritional Supplements
Cannabinoids
Cannabinoid receptors are overexpressed in the skin of dogs with CAD. Palmitoylethanolamide (PEA), an endocannabinoid molecule, appears to decrease the release of histamine, prostaglandin D2, and tumor necrosis factor by canine mast cells in vitro. One study showed improvements in pruritus, skin lesions, and quality of life following supplementation with ultra-micronized PEA, but significant methodological limitations (absence of a control group, data based on owner observation) reduce the value of these results. Studies on CBD and CBDA show variable results.
Conclusion
Diets avoiding allergens play a major role in allergic dogs. Some data suggest the benefit of certain supplements and enriched diets in association with other treatments. Further research, with rigorous methodologies, is needed to better understand the mechanisms of action and confirm the efficacy of these approaches.
Eisenschenk MN. Diet, nutrition, and supplements in canine atopic dermatitis. Vet Clin Small Anim. 2024;54(6):1605-1620. https://doi.org/10.1016/j.cvsm.2024.11.003
