Tart Cherries are among the richest food sources of melatonin, which is a hormone that helps promote sleep. The body's production of melatonin declines with age, which is part of the reason why older adults often have trouble sleeping.
A study in the Journal of Clinical Endocrinology & Metabolism found that small doses of melatonin (0.3 mg) helped insomniacs sleep better. One cup of tart-cherry juice of 1/8 cup dried tart cherries contains roughly 0.3 mg of melatonin.
The recommendation is to eat tart cherries or drink one cup of juice about an hour before bedtime. This is so that the melatonin from the tart cherries can be absorbed by the body.
Note: Sweet cherries also contain melatonin, but not as much as tart cherries.
Source: Bottom Line Magazine, Volume 34 Number 11