Dihydrouridine synthase. Catalyzes the NADPH-dependent synthesis of dihydrouridine, a modified base found in the D-loop of most tRNAs (PubMed:15994936, PubMed:26429968, PubMed:30149704, PubMed:34798057). Negatively regulates the activation of EIF2AK2/PKR (PubMed:18096616).