A small trial involving seven older adults with insomnia has found that when they consumed 8 ounces of tart cherry juice twice daily for two weeks, they were able to sleep more than an hour longer each night (averaging 84 minutes) compared to when they took the placebo, and their sleep tended to be more efficient.
Montmorency tart cherries are a natural source of melatonin, a hormone that helps regulate the sleep-wake cycle. The juice also helped to increase the availability of tryptophan, an essential amino acid and a precursor to serotonin that helps with sleep.
http://www.eurekalert.org/pub_releases/2014-04/wsw-st042814.php