Nutrition and atopic dermatitis.

Atopic dermatitis (AD) is a chronic eczematous disease characterized by T helper 2 (Th2) -shifted allergic immunity, skin barrier impairment, and pruritus. Oral intake of certain nutrients could help regulate AD. In patients with AD, serum 25-hydroxyvitamin D levels are reduced, and oral vitamin D supplementation improves AD. Vitamin D increases regulatory T (Treg) cells which promote tolerance to allergens and prevent allergic inflammation, inducing the expression of filaggrin and cathelicidin in keratinocytes. Vitamin A strengthens Treg cells by inducing the expression of Forkhead box P3, and inhibits mediator release from mast cells or eosinophils. Serum levels of ( (-linolenic acid and its metabolite, dihomo- (-linolenic acid, are reduced in patients with AD, and oral (-linolenic acid improves AD through anti-inflammatory prostaglandin D1 or E1 derived from dihomo- (-linolenic acid. Eicosapentaenoic acid and docosahexaenoic acid ameliorate AD by suppressing the production of leukotriene B4, increasing ceramides in the stratum corneum, or through their metabolites, resolvin E1 and D1, resolving inflammation. Probiotics, Lactobacillus or Bifidobacteria, improve the intestinal permeability barrier, and induce Treg cells. Serum, hair, and erythrocyte zinc levels are reduced in patients with AD. Zinc induces Forkhead box P3 expression and increases Treg cells, and zinc-finger protein A20 suppresses the nuclear factor-κB-dependent expression of inflammatory cytokines or cell-adhesion molecules. Oral supplementation of the above nutrients might play therapeutic or preventive roles for AD.