A cup of warm milk before bed has long been a home remedy for inducing sleep, and a recent study finds evidence that there's a way to increase the sleep-inducing properties of milk naturally.

Researchers from the Uimyung Research Institute for Neuroscience in South Korea found that milk from cows milked at night, known as night milk, has "exceptionally rich amounts of tryptophan and melatonin," according to The Telegraph.

Tryptophan is an amino acid that naturally causes drowsiness. Most of us know it because we feel sleepy after a big dinner involving turkey, because poultry is high in tryptophan. The body converts tryptophan into seratonin, which is eventually converted into melatonin, a natural hormone that helps to regulate our sleep and wake cycles.

Research has not yet been done on humans, but when researchers gave night milk to mice and then put the mice on a rotating cylinder for 20 minutes, the mice became drowsier and fell off the cylinder more than mice who had been given day milk, water or diazepam (the generic name for Valium).

The study suggests that aside from making you extra drowsy, night milk may be a "natural aid for sleep- and anxiety-related disturbances." A study has not yet been conducted on humans, so there's no recommended amount of night milk a human would need to consume to benefit from the additional tryptophan and melatonin in night milk.

More scientific research is needed, of course, but there's one German company that's been profiting from marketing night milk as a sleep aid for several years. Milchkristalle sells patented "milk crystals" that are "rich in natural melatonin and are made from milk, which has been milked at night." The crystals can be added to any beverage and consumed before sleep.

Of course, milk isn't the only source of tryptophan. To get the benefits of tryptophan from a non-animal source, try pumpkin seeds. An ounce of pumpkin seeds contains more than 50 percent of the RDI of tryptophan. They may not, however, have the same psychological effect as a warm glass of milk before bedtime, which is something researchers would certainly need to address. Is there a psychological benefit to milk, something that's been associated with sleep for so long, in addition to the the physiological benefit of the tryptophan?

Robin Shreeves ( @rshreeves ) focuses on food from a family perspective from her home base in New Jersey.