Further, tryptophan is a big molecule that has trouble crossing into the brain, so improving your sleep is not as simple as eating a tryptophan-rich food and getting more serotonin. And, serotonin has multiple functions in the brain, including some that promote wakefulness, so more serotonin does not automatically mean better sleep.
Studies that found a tryptophan effect relied on doses that would require eating a pound of meat at a sitting, Grandner says. "If you're eating so much food to get the tryptophan effect, you might suffer the too-much-food effect."
Other foods, most notably tart cherries, contain melatonin, which does affect sleep. Still, melatonin is not necessarily a sleep aid, says Wilfred Pigeon, a sleep researcher at the University of Rochester. "Studies show it has a very minimal impact on insomnia," he says. "On the other hand, melatonin is a wonderful circadian rhythm shifter."
So if you're a night owl whose body prefers to sleep from 2 a.m. to 9 a.m. but you have to wake up at 7 a.m. every day, melatonin may help you alter your sleep schedule. Pigeon and Grandner say that to get that effect, it would be best to take melatonin at dinnertime rather than at bedtime - and that lower doses (1.5 to 3 milligrams) are better than higher ones. That allows the substance to work with your body's internal clock, starting the long wind-down process that's tied to sundown.
Pigeon conducted a small study with a tart cherry juice that had been developed as a sports drink. The participants - 16 elderly adults with chronic insomnia - reported less wakefulness during the night (by an average of 17 minutes) and more total sleep time (eight minutes) when they drank the juice than when they drank cherry Kool-Aid, which did not contain the melatonin and other phytonutrients found in the sports drink.