Catalyzes the synthesis of 5,6-dihydrouridine (D), a modified base found in the D-loop of most tRNAs, via the reduction of the C5-C6 double bond in target uridines. Specifically modifies U16 in tRNAs. 5,6-dihydrouridine(16) in tRNA + NADP(+) = H(+) + NADPH + uridine(16) in tRNA 5,6-dihydrouridine(16) in tRNA + NAD(+) = H(+) + NADH + uridine(16) in tRNA Belongs to the Dus family. DusC subfamily.