The Role of Nutrition in Dermatology

The skin is the largest organ in the body and as such has a high metabolic demand particularly in situations of disease or trauma. One of the vital roles of the skin is as a barrier-preventing moisture loss (from internal to external surface) and environmental allergen entry (from external to internal surface).¹

The stratum corneum is the external layer of the epidermis and is composed of layers of corneocytes, with a lamellar ‘cement’ containing fatty acids, sterols and ceramide.⁵ This hydrophobic layer functions to prevent trans-epidermal water loss (TEWL).

Balanced and complete nutrition is required for maintenance of a healthy epidermis- including appropriate sources of protein, essential fatty acids, vitamins and trace minerals.

Chandler, M (2018)

Deficiencies in these elements can manifest in dermatological disease with generalised clinical signs related to disruption of the epidermal barrier.² Signs include excessive scale, erythema, alopecia and greasy skin. Secondary bacterial and fungal infections are frequent which can complicate diagnosis of the underlying condition. Diagnosis can be a challenge for clinicians, often impossible on gross examination alone.

When clinical signs are associated with a Cutaneous Adverse Food Reaction (CAFR) then a hydrolyzed elimination diet is the recommended course of action. But in many cases, if the allergens are environmental or the condition is not related to inflammation (dermatosis rather than dermatitis), nutrition still has a role to play in management and recovery. In some conditions, as detailed below, balanced nutrition will rectify a deficiency.

It is always important to take a dietary history, as homemade and vegetarian diets can be extremely difficult to balance appropriately. High dietary levels of phytates (found in certain grains) can bind minerals such as zinc and decrease their bioavailability.¹ High levels of calcium can also interfere with uptake of other minerals.¹ Certain vitamins such as vitamin A and omega 3 fatty acids must be derived from animal sources.

Animals with comorbidities such as malasbsorptive disorders and chronic enteropathies are also more at risk of deficiencies developing over time.

Essential Fatty Acids

In both dogs and cats, dietary sources of linoleic acid (LA) are essential, as LA cannot be synthesized within the body. Cats, in addition cannot synthesize sufficient arachidonic acid (AA) and as such, both LA and AA are considered essential for cats.¹

Vegetable oils such as borage and safflower oil are a very good source of LA, however AA is found in significant amounts only in animal fats. Vitamin E must also be supplemented with the polyunsaturated fatty acids to prevent oxidization.^1,4 Zinc is required for the biosynthesis of fatty acids.

EFAs act as precursors for eicosanoids (prostaglandins and leukotrienes) as well as maintaining the water permeability barrier and regulating epidermal proliferation.

• Omega 6 fatty acid gamma linolenic acid (GLA) promotes production of anti-inflammatory type 1 prostaglandins over type 2 prostaglandins.
• Omega 6 fatty acids maintain fluidity of cell membranes due to their role in ceramide production in the lamellar ‘cement’.
• Omega 3 fatty acids; eicosapentanoic acid (EPA) and docosahexanoic acid (DHA) have anti-inflammatory properties. Fish oils are a much more efficient source of omega 3 than seed oils for both dogs and cats¹.

Omega 3 FAs may have a role in inflammatory skin conditions such as AD, by tipping the balance in favour of anti-inflammatory rather than pro-inflammatory prostaglandin production. It has also been suggested that dogs with AD have reduced ability to convert LA to AA and supplementation of omega 6s in the diet would increase levels in the body.⁴ Recent studies have demonstrated that oral supplementation with PUFAs can improve pruritus in AD. The suspected mechanism is via altered eicosanoid production and improvement in the epidermal barrier.⁵ The ratio in supplementation between omega 3 and 6 fatty acids is key to maximizing benefits.⁴

Vitamin E

Vitamin E is required for maintaining stability of the cell membranes and acts as a free radical scavenger.¹ Lipid metabolism is the main source of oxygen free radicals- and Vitamin E is an effective antioxidant, protecting fatty acids within the stratum corneum.

As such, it is essential to supplement with vitamin E alongside PUFAs in the diet. High fat diets can also create a relative deficiency. It is also important to note that vitamin E levels can become depleted during storage of food due to fat oxidation.⁴ Nearly 40% of homecooked diets are deficient in vitamin E.¹

Protein

Normal growth of hair and epidermal turnover can account for between 25-30% of the animal’s protein requirements daily¹. Hair is composed of 95% protein, mainly from the amino acids cystine and methionine. Phenylalanine and tyrosine are needed for eumelanin formation and provide the black pigmentation with the coat. Tyrosine deficiency will result in the reddening of the black hairs.

Protein deficiency is very rare in clinical practice particularly when feeding a complete commercial diet, but can be seen in chronic conditions such as protein-losing enteropathies.

Zinc

Zinc is required for biosynthesis of fatty acids (deficiencies of the two can be related) and is necessary for the metabolism of Vitamin A as well as maintaining a healthy immune system. Zinc factors in normal epithelialization via keratinocyte migration¹. Zinc deficiency manifests as described- with alopecia, thin hair coat, seborrhea and impaired wound healing. Lesions are often periocular, perioral and around the tarsus¹.

English Bull Terriers suffer with a severe, often fatal, form of skin disease (lethal acrodermatitis) associated with a hereditary defect in zinc metabolism. Alaskan malamutes and Siberian Huskies are breeds with a genetic pre-disposition to zinc-responsive dermatoses.⁴

Treatment in these conditions includes supplementation either orally or systemically until symptoms are resolved. Response should be monitored and doses adjusted if necessary. Excesses of zinc can cause gastrointestinal upset. Treatment often needs to continue for life.⁴

Zinc deficiency can be seen in patients fed a homemade or vegetarian diet. Zinc is better absorbed from animal sources than vegetable sources. Phytates in grains can also interfere with zinc absorption.¹ Also note that puppies (particularly large breed) have a temporary increased need for Zinc, and if the diet is high in calcium, this can interfere with zinc absorption. Vegetarian diets are not suitable for puppies, in particular.¹

Vitamin A

Vitamin A can be ingested in the diet in two forms. Retinoids are found in high numbers in meat, dairy products and eggs. Carotenoids are found in vegetables and are converted into retinol in the upper gastrointestinal tract of humans and dogs. Cats cannot perform this conversion and must consume retinoids from animal sources to maintain vitamin A requirements.¹

Vitamin A is involved in the regulation of growth, vision and differentiation of the epidermis and other epithelial tissues.² Deficiencies and excesses can result in similar clinical signs including hyperkeratosis, scaling and an increase in secondary microbial infections, which can make determination of the cause challenging.

Hypervitaminosis A can be seen clinically in cats fed a diet containing too much liver or over supplementation with cod liver oil.

Cocker spaniels can suffer with a dermatosis that responds to vitamin A supplementation, despite having adequate amounts in the diet. The pathognomonic sign of this condition is the raised hyperkeratotic plaques.^2,4 Most cases respond in time to supplementation of Vitamin A, though this can be in excess of five times the recommended daily amount.²

Vitamin B complexes

The vitamin B complexes are water soluble vitamins and are not stored within the body. They are co-factors in various metabolic reactions, with pantothenic acid (B5) involved in metabolism of fats, carbohydrates and proteins for energy production.

Supplementation with a complex of pantothenic acid, niacin, in combination with choline, inositol and the amino acid histadine have been shown to act synergistically and to decrease transepidermal water loss (TEWL).⁵ The mechanism of action to repair the epidermal barrier is likely due to an increase in ceramide synthesis by corneocytes as demonstrated in the recent study by Watson et al (2006)⁵. Niacin (B3) has been shown to also upregulate the synthesis of skin barrier proteins and choline is a component of phosphatidylcholine. Phospholipid production may be a limiting factor in epidermal turnover and wound healing⁵.

Direct correlation between increased production of ceramides and supplementation with this combination of B vitamins and amino acids was clearly demonstrated in vivo⁵. A progressive improvement in the skin barrier function with supplementation is seen generally over 2-3 months.⁵

Nutrition should be considered a priority in the management of all dermatoses, alongside appropriate systemic and topical therapy. The maintenance of the epidermal skin barrier may markedly improve pruritus and comfort in animals with atopy and will support wound healing. In cases of alopecia and changes in pigmentation, correction of deficiencies by providing a targeted complete diet will be more effective than simply a maintenance commercial diet.

Dietary supplementation may be required for an extended duration, even lifelong; thus selecting a complete diet specifically designed for such cases improves compliance and satisfaction for both the client and the patient.

Royal Canin Skin Support and Skin and Coat are designed to support management and recovery from dermatoses and alopecia. The canine and feline diets provide complete nutrition for adult pets, and contain the appropriate omega 3 and 6 ratios, antioxidants (Vitamin E, C, Taurine and polyphenols) and vitamin B complexes for optimal skin health.

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References:

1. Chandler, M. (2018) Dietary Therapy for dermatological disorders in companion animals The Veterinary Times available [online] https://www.vettimes.co.uk/article/dietary-therapy-for-dermatological-disorders-in-companion-animals/
2. Miller, W., H., (1989) Nutritional Considerations in Small Animal Dermatology Veterinary Clinics of North America: Small Animal Practice. Vol 19:3 497-511
3. Rees, C. A., et al (2001) Effects of dietary flax seed and sunflower seed supplementation on normal canine serum polyunsaturated fatty acids and skin and hair coat condition scores Veterinary Dermatology Vol 12 111-117
4. Watson, T.D.G., (1998) Diet and Skin Disease in Dogs and Cats The Journal of Nutrition Vol 128:12 2783-2789
5. Watson, A. L., et al (2006) Dietary constituents are able to play a beneficial role in canine epidermal barrier function Experimental Dermatology 15:74-81
6. Witzel-Rollins, A. (2019) Non-controlled, open label clinical trial to assess the effectiveness of a dietetic food on pruritis and dermatological scoring on atopic dogs BMC Veterinary Rese

Postdate: 30th June 2020