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 might help regulate AD. Serum 25-hydroxyvitamin D levels are often low in patients with AD, and oral vitamin D supplementation improves AD. Vitamin D increases regulatory T (Treg) cells, which promote tolerance to allergens and prevent allergic inflammation by inducing expression of filaggrin and cathelicidin in keratinocytes. Vitamin A strengthens Treg cells by inducing expression of forkhead box P3 and inhibits mediator release from mast cells and eosinophils. Serum levels of γ-linolenic acid and its metabolite, dihomo-γ-linolenic acid, are low in patients with AD, and oral γ-linolenic acid improves AD through anti-inflammatory prostaglandin D and E derived from dihomo-γ-linolenic acid. Eicosapentaenoic acid and docosahexaenoic acid ameliorate AD by suppressing production of leukotriene B, increasing ceramides in the stratum corneum, and through their metabolites, resolvin E1 and D1, which resolve inflammation. The probiotics Lactobacillus and Bifidobacteria improve the intestinal permeability barrier and induce Treg cells. Zinc levels in serum, hair, and erythrocytes are diminished in patients with AD. Zinc induces forkhead box P3 expression and increases Treg cells, and zinc-finger protein A20 suppresses nuclear factor-κB-dependent expression of inflammatory cytokines and cell-adhesion molecules. Oral supplementation of the above nutrients might have therapeutic or preventive roles in AD.