ARA; C20:4 n6 is an omega-6 long-chain polyunsaturated fatty acid (LCPUFA). It is formed by elongation and desaturation from the essential linoleic acid (LA, C18:2 n6). ARA is precursor to more than 100 metabolites many of whom the function remains unknown. Best investigated is the class of eicosanoids that make ARA a potent tissue dependent signal transducer and involved in immune responses for example as pro- and anti-inflammatory mediator and regulator (e.g. prostaglandin E2) or anaphylaxis were its metabolites (e.g. leukotrienes) affect vascular permeability and smooth muscle contraction; Other metabolites regulate platelet aggregation, vasoconstriction, hormone, muscle, bone and cartilage formation. Together with DHA, ARA is required for brain development. The relevance of ARA in infancy and childhood has been thoroughly reviewed by (Hadley et al. 2016; Koletzko and Innis. 2005).