Catalyzes the regio- and stereoselective reversible NAD-dependent reduction of (6R)-2,2,6-trimethyl-1,4-cyclohexanedione (levodione) to (4R,6R)-4-hydroxy-2,2,6-trimethylcyclohexanone (actinol). (4R)-hydroxy-(6R)-2,2,6-trimethylcyclohexanone + NAD(+) = (6R)-2,2,6-trimethyl-1,4-cyclohexanedione + H(+) + NADH Strongly activated by monovalent cations, such as K(+), Na(+), and NH4(+). Belongs to the short-chain dehydrogenases/reductases (SDR) family.