IL4 and food allergy: However, our study extends this paradigm in three key dimensions: First, our U-shaped risk curve reflects dual genetic modulation: (i) risk amplification via Th2-pathway variants (IL4R/IL-4/IL13) under low vitamin D; (ii) protection attenuation in FcεRIβ (MS4A2) carriers at high vitamin D. Second, we establish this U-shaped relationship for clinically confirmed food allergy—a distinct phenotype from respiratory outcomes.