There is some evidence that sleep may help the liver regenerate. In a study of rats, researchers found that those who slept more had better liver function than those who slept less. The researchers believe that sleep helps the body to repair and rejuvenate itself, including the liver.
In another study, people with chronic liver disease were found to have better quality sleep than those without the disease. The researchers believe that this is because the liver needs time to rest and heal during sleep.
So, while there is no definitive proof that sleep helps the liver specifically, it does appear that getting enough rest and relaxation in general may be beneficial for this important organ.