Oxidoreductase involved in lignan biosynthesis (PubMed:11606193). Catalyzes the NADPH-dependent reduction of phenylcoumaran benzylic ethers (PubMed:11606193). Converts dehydrodiconiferyl alcohol (DDC) to isodihydrodehydrodiconiferyl alcohol (IDDDC) (PubMed:11606193). (-)-dehydrodiconiferyl alcohol + H(+) + NADPH = (S)-isodihydrodehydrodiconiferyl alcohol + NADP(+) (+)-dehydrodiconiferyl alcohol + H(+) + NADPH = (R)-isodihydrodehydrodiconiferyl alcohol + NADP(+) May cause an allergic reaction in human (PubMed:9519865, PubMed:11606193, PubMed:10550744). Binds to IgE from patients allergic to birch pollen (PubMed:9519865, PubMed:11606193, PubMed:10550744). Induces histamine release from basophils of patient allergic to the birch pollen protein Bet v 6 (PubMed:10550744). Exhibits cross-reactivity with IgE from patients allergic to fruits and vegetables (PubMed:9519865, PubMed:11606193, PubMed:10550744). May be a minor allergen of birch pollen (PubMed:9519865, PubMed:11606193, PubMed:10550744). Belongs to the NmrA-type oxidoreductase family. Isoflavone reductase subfamily.