The findings suggest that the drink could join blueberries and other polyphenol-rich fruits as an anti-ageing food. A blueberry-enriched antioxidant diet was recently found to prevent an age-related increase in the protein NF-kappaB that responds to oxidative stress, a probable cause of brain ageing.
The researchers, from the US department of agriculture's Human Nutrition Research Center on Aging, subjected 45 mature rats approaching the end of their expected life spans to a range of tests and challenges commonly accepted as methods of measuring changes in short-term memory and neuro-motor skills.
"Concord grape juice appeared to reduce or reverse the loss of sensitivity of muscarinic receptors, thus enhancing cognitive and some motor skills in the test animals. In many of the tests we saw significant improvements or trends toward improvement," reported James A. Joseph, lead researcher in the study, at the 1st International Conference on Polyphenols and Health held last month in Vichy, France.
The Concord grape is a dark-blue variety, native to North America, and used widely in juice and wine production. Like cranberries, the grape has been studied closely for its high antioxidant content. Its juice has been shown to lower blood pressure and daily consumption for just eight weeks significantly improved arterial function in a recent trial.
Joseph's team used the Morris water maze to test memory. It is an age-sensitive challenge that requires animals to use spatial learning to find a platform submerged 2 cm below the surface of a pool of water. Rats fed a 10 per cent solution of Concord grape juice found the platform in roughly 20 per cent less time than the control group.
Other tests measured the animals' ability to balance on a horizontal stationary rod; a rotating, slowly accelerating rod; and various sized planks, and their ability to hold onto a suspended wire and an inclined wire screen. Some of those tests saw improvements in either or both of the group consuming a 10 per cent solution of Concord grape juice and the group consuming a 50 per cent solution.
Joseph added that the findings were not surprising. "We have seen similar effects in the work we've done in blueberries."
The researchers point to several factors as potential mechanisms of action, including increased dopamine production and a potent overall antioxidant effect.
"As our population ages, we are continually looking for ways to maintain our mental and physical skills," said Joseph. "While these laboratory animal studies are certainly preliminary and much more work needs to be done, we know that consuming high levels of natural dietary antioxidants is a good thing from a number of perspectives. And it appears that drinking Concord grape juice has the potential to help retard the mental and physical declines of ageing."
The pace of polyphenol research has increased rapidly over the past five years although clinical and epidemiological evidence of their protective effects is still limited and researchers are still working to establish optimal levels of intake. A growing number of new food products, designed as sources of polyphenols, are being introduced to target consumer interest in health.