Certain Italian grape varieties used in popular red wines may contain high levels of the sleep hormone melatonin, according to an analysis by Marcello Iriti, Mara Rossoni, and Franco Faoro at the University of Milan. The discovery might explain why so many of us who dine with Bacchus in the evening, wind down so easily after a hard day's slog. However, the team is yet to carry out a definitive gas chromatography-mass spectrometry (GC-MS) analysis and other scientists are skeptical of their findings.

"The melatonin content in wine could help regulate the circadian rhythm, the sleep-wake pattern, just like the melatonin produced by the pineal gland in mammals," suggests Marcello. Melatonin, N-acetyl-5-methoxytryptamine, is secreted naturally by the pineal gland in the brain, especially at night. It tells the body when it is time to sleep and recent research has linked a lack of melatonin with various cancers.

Until recently, scientists considered melatonin to be a compound produced exclusively by mammals. Some researchers reckon plants too could produce this compound. Melatonin has also been shown to have antioxidant properties. Russel Reiter and colleagues at the University of Texas Health Science Center, in San Antonio, reviewed the literature and explained how melatonin directly detoxifies the hydroxyl radical (OH), hydrogen peroxide, nitric oxide, peroxynitrite anion, peroxynitrous acid, and hypochlorous acid.

Iriti and colleagues claim to have found high levels of melatonin in Nebbolo, Merlot, Cabernet Sauvignon, Sangiovesse, and Croatina grape varieties, and have demonstrated that the melatonin content of the grapes can be enhanced by treating the fruiting vines with the plant "vaccine" benzothiadiazole. This compound has been found to induce systemic acquired resistance—an important component of disease resistance—in several plant species.

Other scientists are skeptical of the findings. Richard Wurtman of the brain and cognitive science department at Massachusetts Institute of Technology, for instance, is unconvinced by the analysis, which used high performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA), and believes further research is needed to determine whether the compounds discovered are melatonin, or something very similar. "The authors identified what they thought was melatonin by using two assays—one based on chromatography and the other on antibody binding—that no responsible chemist would find satisfactory," Wurtman told Reactive Reports. He adds that, "The only acceptable method for demonstrating that what they were measuring was melatonin would be by GCMS."

Other researchers have found that when GCMS is applied to confirming the presence of melatonin in other foods and biological materials it has invariably been shown that that "melatonin" was not present. So, if you're winding down with a glass of wine, the effect may be down to nothing more than good old alcoholic intoxication rather than a hormonal antioxidant effect.

J Sci Food Agric, 2006, 86, 1432-1438; http://dx.doi.org/10.1002/jsfa.2537

Nutr Rev, 2001, 59, 286-290; http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?
cmd=Retrieve&db=PubMed&list_uids=11570431&dopt=Abstract

http://wurtmanlab.mit.edu/publications.php#mela