Scientists from the University of Leeds (United Kingdom), Quadt Consultancy BV (The Netherlands), and Welch Foods Inc. (USA) report that, while there significant improvements for everyday tasks such as driving following grape juice consumption, there were no effects on most cognitive outcomes.
“Previous interventions that demonstrated the benefits of Concord grape juice have been performed exclusively in older adults with mild cognitive impairment; thus, this is the first study to our knowledge to demonstrate cognitive benefits after Concord grape juice in healthy middle-aged adults,” they wrote in the American Journal of Clinical Nutrition.
“Combined with another recent study [Kean et al., Am J Clin Nutr, 2015, Vol. 3, pp. 506–14] that showed that executive function and memory improvements after the consumption of flavanone-rich orange juice, these results indicate that cognitive benefits achieved from regular daily flavonoid consumption are not exclusive to adults exhibiting cognitive decline or neurodegenerative disease.”
Led by Louise Dye, Professor of Nutrition & Behaviour at the University of Leeds, the researchers recruited 25 healthy, middle-aged working mothers aged between 40 and 50 to participate in their randomized crossover study. The women were randomly assigned to receive either 355 mL (12 oz) per day of Concord grape juice or an appearance-matched placebo for three months. The grape juice provided 777 mg of polyphenols per day. A four week “washout” period followed the intervention and the women were then crossed over to the other group for a further three months.
Results showed that grape juice consumption was associated with significant improvements in immediate spatial memory and driving performance, compared to placebo. However, no significant effects were observed for verbal recall or executive function, including general reaction times.
Improvements in reaction times during driving tests were reported by the researchers, as evidenced by better steering accuracy and reaction times when following a car. “The observed effects would account for a reduction in stopping distance of about 11 meters at the speeds driven (40–60 mph), which is an important safety benefit,” wrote the researchers. “Thus, the cognitive effects of long-term Concord grape juice consumption translate into meaningful outcomes on everyday tasks.”
Some caution is required when interpreting the results because the washout period may have been insufficient and some residual effects were carried over into the control phase, said the researchers.
“The combination of the enduring and practice effects may have masked some of the potential effects of the Concord grape juice, particularly in this healthy middle-aged sample in which the effects of nutritional interventions are likely to be small,” they wrote.
“These findings have clear implications for the design of future crossover interventions and indicate that the cognitive effects of Concord grape juice are not exclusive to older adults and adults with neurodegenerative disease. Future studies should seek to explore the strength and length of cognitive effects after the cessation of flavonoid supplementation.”
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.115.114553
“Concord grape juice, cognitive function, and driving performance: a 12-wk, placebo-controlled, randomized crossover trial in mothers of preteen children”
Authors: D.J. Lamport, et al.