Scientists in Italy say they have discovered that the grapes used to make some of the most popular red wines contain high levels of the sleep hormone melatonin. The hormone is naturally secreted by the pineal gland in the brain, especially at night. It tells the body when it is time to sleep, reports www.bbr.com, Web site of the London-based wine merchants, Berry Bros. & Rudd.

The researchers, from the University of Milan , said the discovery of melatonin in grape skins could explain why so many of us reach for a bottle of red wine to help us wind down after a long day.

"The melatonin content in wine could help regulate the circadian rhythm [sleep-wake patterns], just like the melatonin produced by the pineal gland in mammals," says researcher Iriti Marcello.

Until recently, melatonin was thought to be exclusively produced by mammals, but has recently been discovered in plants. It is thought to have antioxidant properties. Iriti's study discovered high levels of melatonin in Nebbiolo, Merlot, Cabernet Savignon, Sangiovesse and Croatina grape varieties.

Iriti's team has also shown that melatonin content can be enhanced in grapes by treating vines with a plant vaccine named Benzothiadiazole.

Richard Wurtman of the brain and cognitive science department at MIT is unconvinced, however, and believes further research is needed to determine whether the compounds discovered are melatonin, or something very similar.