After taking retinol to the cells, RBP is catabolized, and disposed of by the kidney. Retinol is mainly disposed of via fecal excretion, and a small amount is lost in the urine. These cellular binding proteins are also involved in the directing of vitamin A to certain enzymes. Retinol carried by CRBP is more-easily esterified to retinaldehyde than unbound retinol. Retinoic acid has been suggested to have a feedback mechanism.
Increased levels spare the degradation of retinol - at least in rats.
When there is an increase of retinoic acid levels, LRAT activity increases, and vice versa in deficiency. LRAT directs the chylomicron's retinyl esters to storage in the liver. A deficiency of retinoic acid affects the cells lining the lungs and trachea. Research is showing that retinoic acid may delay or prevent some skin cancers. Retinoic acid has been used to treat dermatological problems, but the safety of this is not clear.