News about a possible link between grapes and the sleep hormone appears in the Journal of the Science of Food and Agriculture's early online edition.
Researchers included Marcello Iriti, PhD, of Milan's Istituto di Virologia Vegetale (Institute of Vegetable Virology).
They tested extracts from eight types of grapes -- Nebbiolo, Croatina, Sangiovese, Merlot, Marzemino, Cabernet Franc, Cabernet Sauvignon, and Barbera -- for melatonin and found evidence of the hormone.
Most to Least Melatonin
The grapes all came from the same vineyards in northeastern Italy and were at the same stage of maturity. Some came from plants treated with benzothiadiazole, a synthetic chemical that helps plants ward off disease.
Iriti's team used two different tests to check for melatonin and found varying amounts among the varieties. On both tests, Nebbiolo grapes showed the most melatonin, followed by Croatina grapes. Merlot from plants treated with benzothiadiazole ranked third.
Treating grapevines with benzothiadiazole might increase melatonin in grapes, Iriti and colleagues note.
As for the other grape varieties, they all showed some amount of melatonin on both tests, but their rankings varied.
The researchers didn't check melatonin levels in wine, but they point out that melatonin might get a boost from the antioxidants and alcohol in wine.
Maybe Not Melatonin?
Plants don't sleep. So why would they need melatonin?
Melatonin might help defend against plant diseases, write Iriti and colleagues.
But not all experts are convinced grapes in fact contain the substance.
The journal's sister publication, Chemistry & Industry, also has a news story about Iriti's study (both publications come from the London-based Society of Chemical Industry).
In the Chemistry & Industry article, Richard Wurtman, MD, of the Massachusetts Institute of Technology, is quoted questioning whether Iriti's team might have actually found a close chemical cousin of melatonin -- not melatonin itself -- in the grapes.
WebMD contacted University of Milan plant pathology professor Franco Faoro, PhD, who worked on Iriti's study, for a response.
Faoro's email to WebMD doesn't directly address the possibility that the grapes didn't contain melatonin: "I would like to stress, as reported in the paper, that melatonin content in grape berry is very variable, depending on the varieties, and, possibly on the growing conditions," Faoro writes.