One of the most important functions of the skin is as a barrier. It prevents water loss (inside-outside barrier) and protects the body from the environment (outsideinside barrier). The barrier function is dependent on the stratum corneum (SC). It has been suggested that atopic dermatitis (AD) is associated with a defective barrier function. One study which assessed barrier function with transepidermal water loss (TEWL, the volume of water passing from inside to outside of the body through the upper epidermal layers) found a higher TEWL in dogs with AD vs. controls.1 Treated AD dogs had lower TEWL compared to non-treated, suggesting skin barrier function can be improved by treatment. Nutrition is important to ensure the healthy skin barrier.2 It is not fully known whether nutritional modification can improve the skin barrier function in dogs and cats with disease, although there is some promising research in this area.
Nutrient Deficiencies and Skin Disease
The skin is the largest organ in the body with a high turnover rate, thus, several nutrient deficiencies can result in skin problems,3,7 including protein and some amino acids, omega 6 essential fatty acids, trace elements, lipid soluble vitamins and B vitamins. These deficiencies are unlikely in healthy pets fed complete and balanced diets. Unbalanced homemade diets can result in all of these deficiencies.
Protein: Hair is 95% protein and certain amino acids are especially important for healthy hair, e.g., methionine, cysteine, and tyrosine. Protein deficiency can cause thin, dull brittle hair, and tyrosine deficiency can cause a loss of dark hair pigment.
Zinc: Zinc dependent metalloproteinases are involved in keratinocyte migration and wound healing. Several syndromes are associated with zinc deficiency, including Syndrome I in Huskies and Malamutes associated with zinc malabsorption and Syndrome II in puppies fed a zinc deficient diet.
Fat Soluble Vitamins
Vitamin A deficiency can cause skin scaling, poor hair coat, and alopecia. Vitamin A is very important for all epithelia and its deficiency results in altered skin barrier function but there is no data to support its supplementation to help skin barrier.
Vitamin E, an antioxidant, protects fatty acids (including those in the SC) from damage. Deficiency can result in pansteatitis (e.g., cats fed a raw fish diet) resulting in firm painful swellings due to inflammation from adipose tissue perioxidation. One study found dogs with atopy had lower plasma vitamin E and that supplementation (8.1 IU/kg q 24 hours for 8 weeks) improved the subjective pruritus score; however, it is unknown if this relates to improvement of skin barrier function.8
B Vitamin Deficiencies
Deficiencies of biotin, riboflavin niacin and pyridoxine may be associated with skin disorders. One study found a positive effect on TEWL of healthy dogs with a diet supplemented with pantothenic acid, niacin, choline, inositol, and histidine. These nutrients showed in vitro stimulation of ceramide synthesis in canine keratinocytes.6 One small study with Labrador puppies fed this combination of nutrients suggested that it could help reduce itch when fed for one year.9 However, there is very little data on the effects of supplementing these nutrients separately and no data on how does this combination work to improve skin barrier function.
Essential Fatty Acids
Essential fatty acids (EFA) are fatty acids from the omega 6 and 3 families. Linoleic acid is an omega 6 EFA that is incorporated in the ceramides of the SC4 and deficiency results in dry, coarse skin. High fat diets or vegetable oil supplements like corn oil can improve hair coat quality in dogs. Omega 6 EFA are more potent than omega 3s for skin barrier function. Oral supplementation with EFA (especially linoleic acid) can improve ceramide synthesis in dogs, although the studies are still scarce and more data is needed to confirm its effect and the appropriate route, dose and composition of the treatment.5
Omega 3 fatty acids (e.g., eicosapentanoic and docosahexaenoic acid) result in cytokine production with less inflammatory characteristics than omega-6 EFAs and may decrease pruritus in dogs10 and skin inflammatory responses in cats11.
Microbiome and Probiotics
The sequencing of bacterial 16S rRNA genes shows the human skin surface inhabited by a highly diverse and variable microbiota; similarly, dogs’ skin is also inhabited by rich and diverse microbial communities.12 Sequence data shows high individual variability between samples. Differences in species richness and was also seen between healthy and allergic dogs, with allergic dogs having lower species richness compared to healthy dogs.
Probiotic products differ widely in composition and number of microbes; however, there is some evidence that some products have an immunomodulatory effect. Their use has been suggested as an adjunct treatment for canine AD. Administration of the probiotic strain Lactobacillus sakei probio-65 for 2 months significantly reduced the disease severity index in experimental dogs AD13. Another study showed probiotic K71 used as a complementary therapy provided a corticosteroid and ciclosporin sparing effect.14
Effect of Food Processing
Food processing including heating can decrease or increase the allergenicity, generally decreasing it by destroying conformational epitopes, although the Maillard reaction (glycation when heating amino acids and reducing sugars, e.g., browning of foods) may increase it (Norwak-W). An abstract on a small study in dogs showed raw horse meat and canned products had less proteins reacting with IgE compared to dry foods and cooked horse/potato; cooked fish proteins were less reactive with IgE compared to raw.15
References
1. Cornegliani L, Vercelli A, Sala E, Marsella R. Transepidermal water loss in healthy and atopic dogs, treated and untreated: a comparative preliminary study. Vet Dermatol. 2011;23:41–44.
2. Hensel P. Nutrition and skin diseases in veterinary medicine. Clin Dermatol. 2010;28:686–693.
3. National Research Council. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press; 2006.
4. Reiter LV, Torres SM, Wertz PW. Characterization and quantification of ceramides in the nonlesional skin of canine patients with atopic dermatitis compared with controls. Vet Dermatol. 2009;20:260–266.
5. Popa I, Pin D, Remoué N, et al. Analysis of epidermal lipids in normal and atopic dogs, before and after administration of an oral omega-6/omega-3 fatty acid feed supplement. A pilot study. Vet Res Commun. 2011;35:501–509.
6. Watson AL, Fray TR, Bailey J, Baker CB, Bever SA, Markwell PJ. Dietary constituents are able to play a beneficial role in canine epidermal barrier function. Exp Dermatol. 2006;15:74–81.
7. Outerbridge CA. Nutritional management of skin diseases. In: Fascetti AJ, Delaney SJ, eds. Applied Veterinary Clinical Nutrition. Chichester, UK: Wiley Blackwell; 2012:157–174.
8. Plevnik Kapun A, Salobir J, Levart A, et al. Vitamin E supplementation in canine atopic dermatitis: improvement of clinical signs and effects on oxidative stress markers. Vet Rec. 2014;175(22):560.
9. van Beeck FL, Watson A, Bos M, Biourge V, Willemse T. The effect of long-term feeding of skin barrier-fortified diets on the owner-assessed incidence of atopic dermatitis symptoms in Labrador retrievers. J Nutr Sci. 2015;12;4:e5.
10. Logas D, Kunkle G. Double-blinded crossover study with marine oil supplementation containing high-dose eicosapentaenoic acid for the treatment of canine pruritic skin disease. Vet Dermatology. 1994;5(3):99–104.
11. Park H, Park JS, Hayak MG, et al. Dietary fish oil and flaxseed oil suppress inflammation and immunity in cats. Vet Immunol Immunopathol. 2011;141(3–4):301–306.
12. Rodrigues Hoffmann A, Patterson AP, Diesel A, et al. The skin microbiome in healthy and allergic dogs. PLoS One. 2014;9(1):e83197.
13. Kim H, Rather IA, Kim H, et al. A double-blind, placebo controlled-trial of a probiotic strain Lactobacillus sakei probio-65 for the prevention of canine atopic dermatitis. J Microbiol Biotechnol. 2015;25(11):1966–1969.
14. Ohshima-Terada Y, Higuchi Y, Kumagai T, Hagihara A, Nagata M. Complementary effect of oral administration of Lactobacillus paracasei K71 on canine atopic dermatitis. Vet Dermatol. 2015;26(5):350–3, e74–5.
15. Favrot C, Couturier N, Bihain B. Food processing is associated with changes in the IgE sensitization profile in dogs. Abstract. Vet Dermatology. 2016:27:68.