Are vitamin D and atopic dermatitis related?

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Vitamin D together with parathormone regulates calcium and phosphate homeostasis, acting on various organs (intestine, bone tissue, kidney) maintaining normal skeletal architecture. The skin also turns out to be a central organ in vitamin D metabolism where by the action of sunlight it is converted to pre-vitamin D3 which within a few hours undergoes further transformation (isomerization) to vitamin D3 (cholecalciferol). Vitamin D is involved in regulating the synthesis of lipids (glucosylceramides) that are a component in skin barrier function. It also takes several actions in immune system homeostasis and protection from bacteria and fungi.

Vitamin D3, the portion synthesized at the skin level and that part introduced with food, is metabolized at the liver level by transforming into calcifediol (25-OH-D3), representing the main circulating metabolite. In turn, calcifediol is by the kidneys further transformed into calcitriol (1,25-OH-2D3), which turns out to be its active form to carry out its biological activity by activating its receptors distributed throughout the body, thus explaining its extraskeletal activity.

Skin synthesis of vitamin D is influenced by various factors such as: phenotype, age, exposed skin surface area, use of sunscreens, seasonality, latitude and exposure time. It is low in foods, with the major dietary source being animal fats especially fatty fish (salmon and herring)

Atopic dermatitis (also called atopic eczema) is a very common condition and is the most common inflammatory skin disease. It mainly affects children, accounting for about 20%, while the adult population accounts for about 5%. It is characterized by periods of remission and others of flare-ups. The origin of atopic dermatitis can be related to allergic and nonallergic factors, also called extrinsic form (IgE-mediated and Th2 lymphocytes) and intrinsic form (other mediators and Th1 lymphocytes), and shows alterations in the formation and regulation of the skin barrier and a dysregulation in the immune response.

The characteristics of atopic dermatitis are represented by eczematous lesions, intense itching and chronic course, assuming a relapsing remitting course that generally improves with sun exposure. In the acute phase, the lesions are erythematous-vesicular and chronically becoming erythematous-squamous and lichenified. The same topography differs with age. In the infant, atopic dermatitis may present as a milky scalp crust and then spread to the face and limbs with exudating lesions, characteristically sparing the midfacial region. In children and adolescents, lesions are outlined at the folds of the limbs with involvement of the face, neck, and upper trunk. Finally, atopic dermatitis in adults manifests as chronic eczema of the hands or face (with characteristic involvement of the eyelids) and neck.

Discussion

Multiple epidemiological studies have demonstrated an inverse correlation between prevalence of atopic dermatitis and latitude, reduced sun exposure, and hypovitaminosis D. Atopic dermatitis has been associated with vitamin D deficiency in both pediatric and adult age. Studies have reported that about 50% of children with this disorder reported low serum vitamin D levels of less than 10 ng/ml. Although the association between atopic dermatitis and low vitamin D values has been demonstrated, its supplementation is controversial; in fact, in some studies it has been shown that there is insufficient evidence to recommend the use of vitamin D in atopic dermatitis, and therefore it is not possible to issue a recommendation on its use in the treatment of atopic dermatitis. Other reviews also conclude that there are no conditions to suggest the use of vitamin D. In contrast, other studies have shown that vitamin D supplementation can improve the severity of atopic dermatitis especially in children with low amounts in their bodies. Most recent studies have indicated that supplementation at doses between 1000 IU/day and 2000 IU/day is associated with improvement in atopic dermatitis as assessed by scores:

  • SCORAD (Clinical Evaluation of Atopic Dermatitis), which assesses intensity by considering the following parameters: erythema, edema and papules, secretion and crusting, excoriation, lichenification, and skin dryness;
  • EASI (Eczema Area and Severity Index) which evaluates the skin component.
  • While with dosages of 800 IU/day for 6 weeks or 4000 IU/day for 21 days gave poor results, with no improvement in atopic dermatitis.

One prospective cohort study observed that children who had received a high dietary intake of vitamin D between 5 and 10 months of age had an increased risk of developing atopic dermatitis at 6 years of age. Thus other studies have looked for an association between maternal vitamin D levels and risk of atopic dermatitis in the unborn child, but with mixed results.

Conclusions

Vitamin D plays an important role in the regulation of healthy skin and in the pathogenesis of some inflammatory and immune-mediated skin diseases such as atopic dermatitis. Vitamin D deficiency is a risk factor for atopic dermatitis, so its dosage, especially in reverse, is recommended in patients with this condition. Vitamin D dosing is also recommended in patients who have been on corticosteroid therapy for a long time, either systemic or local use. If a condition of hypovitaminosis D is found, supplementation can be done. Also according to U.S. studies, supplementation with vitamin D, which is also available as an equivalent drug, can reduce the severity of atopic dermatitis especially in children who have low amounts of this vitamin in their bodies. Therefore, it can be concluded that children with atopic dermatitis with low levels of vitamin D, or which otherwise decrease during winter, may benefit from vitamin D supplementation.

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