Although its dehydrogenase activity is NAD-specific, it can also utilize NADP at a reduced efficiency. (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + NAD(+) = 5,10-methenyltetrahydrofolate + NADH 5,10-methenyltetrahydrofolate + H2O = (6S)-10-formyltetrahydrofolate + H(+) Belongs to the tetrahydrofolate dehydrogenase/cyclohydrolase family.