Cherries are a rich source of the natural hormone melatonin, which helps to regulate your sleep-wake cycle (circadian rhythm) and allow you to achieve a deep, refreshing sleep. Melatonin is traditionally taken to relieve jet-lag and help re-establish normal sleeping patterns in people who travel across several time zones.
However, other factors can disrupt sleep besides international travel. Stress is a common cause of disturbed sleeping patterns. Autoimmune disease and chronic fatigue syndrome are notorious for causing disrupted sleeping patterns and many patients feel better on a melatonin supplement.
Most studies on sleep quality using cherries have relied on cherry juice. This can be problematic because not all varieties of cherries are a good source of melatonin (the tart Montmorency cherry is mostly used), and cherry juice can be a significant source of sugar.
However it is a good idea to include some cherries in your diet regularly, particularly as a treat after dinner.
You can obtain a much stronger dose of melatonin by taking a supplement in tablet form.