The role of vitamin D is well known in calcium and phosphate homeostasis; however, in addition to traditional functions, vitamin D has an important role in pathogenesis of different allergic diseases, such as asthma, atopic dermatitis (AD), and food allergy. There are evidences that lower cord blood vitamin D status is observed in infants with eczema. More-over, vitamin D level is decreased in subjects with asthma. One of the most important functions of vitamin D is to modulate the immune system response, both innate and adaptive, by suppressing Th2-type response and increasing natural killer cells. Vitamin D induces a higher level of IL-10, which is known as anti-inflammatory cytokine. Other studies have shown that vitamin D contributes to the conversion of CD4+ T cells to T regulatory cells. Recent studies showed that higher serum 25-hydroxyvitamin D level was associated with a reduced risk of asthma exacerbation and hospitalization. Vitamin D can enhance dexamethasone-induced MAP kinase phosphatase-1 (MKP-1) expression in peripheral blood mononuclear cells. Experimental data suggest that vitamin D can potentially increase the therapeutic response to glucocorticoid and can be used as an add-on treatment in steroid-resistant asthmatics. Vitamin D stimulates the production and regulation of skin antimicrobial peptides, such as cathelicidins, which have both direct antimicrobial activity and induced host cellular response by triggering cytokine release. Recent evidence suggests that low blood vitamin D level is a risk factor for food allergy.

Vitamin D acts by binding to the vitamin D receptors (VDRs), which are located in a variety of tissues. VDRs have been identified on nearly all cells of the immune system including T cells, B cells, neutrophils, macrophages, and dendritic cells (DCs).

Vitamin D deficiency predisposes to gastrointestinal infections by changing gut micro-biota, which may promote the development of food allergy. However the detail mechanism how vitamin D affects or protects the development of allergic diseases is still unknown. Vitamin D level is determined by sun exposure.

Due to the fact that Lithuania, Latvia and Taiwan are located in different latitudes of north hemisphere with markedly different sun exposure, in this Joint collaboration study between Taiwan, Lithuanian and Latvia, we are going to study, (1). Serum vitamin D level in children and adults with AD and/or asthma in Lithuania, Latvia and Taiwan. (2). VDRs genetic polymorphisms of AD and/or asthma in children and adults in Lithuania, Latvia and Taiwan. (3). Finally, we would like to explore the gut microbiome of patients with AD and/or asthma in Lithuanian, Latvian and Taiwanese children and adults; and to estimate possible relationship between gut microbiome and vitamin D level and VDRs genetic polymorphisms. We believe that this study will be the first which compares the populations with different geographical and ecological factors having the same allergic diseases. We hope that these results will provide the answer about the role of vitamin D in the prevention, or in the future, in treatment of allergic diseases.

Inclusion Criteria:

• Patients with mild to moderate asthma
• Patients with mild to moderate atopic dermatitis
• Healthy individuals

Exclusion Criteria:

• Acute or chronic infections
• Oncological diseases
• Acute systemic autoimmune diseases
• Use of systemic immunosuppressants (wait 1 month)
• Use of vitamin D supplementation
• Use of systemic antihistamines (wait 1 week)

Children and adults with mild to moderate asthma or mild to moderate atopic dermatits.

Healthy individuals as control group.