November 2, 2016

Grape Juice Improves Driving in Stressed Working Mothers

Common fruit yields uncommon benefits
Placebo-controlled study demonstrates the benefits of flavonoid-rich grape juice for women who live life in the fast lane.


Lamport DJ, Lawton CL, Merat N, et al. Concord grape juice, cognitive function, and driving performance: a 12-wk, placebo-controlled, randomized crossover trial in mothers of preteen children. Am J Clin Nutr. 2016;103(3):775-783. 


This 12-week randomized crossover design study with a 4-week washout measured whether Concord grape juice (CGJ) consumption improved cognitive function as measured by driving performance in women exposed to moderate chronic stress. Participants were assigned to 1 of 2 orders (CGJ then placebo or placebo then CGJ) according to a counterbalanced randomization schedule prepared by an independent statistician.


Twenty-five healthy mothers (aged 40-50 years) of preteen children who were employed for ≥30 hours per week.

Study Medication and Dosage

Participants consumed 12 ounces (355 mL) of either Concord grape juice (CGJ) (containing 777 mg total polyphenols) or an energy-, taste-, and appearance-matched placebo daily.

Outcome Measures

Verbal and spatial memory, executive function, attention, blood pressure, and mood were assessed at baseline and at 6 and 12 weeks. Immediately after the cognitive battery, a subsample of 17 women completed a driving performance assessment at the University of Leeds Driving Simulator. The 25-minute driving task required participants to match the speed and direction of a lead vehicle.
The benefits appeared to persist even when the study participants were no longer drinking grape juice.

Key Findings

Significant improvements in immediate spatial memory and driving performance were observed after CGJ relative to placebo. There was evidence of an enduring effect of CGJ such that participants who received CGJ first followed by placebo maintained better performance in the placebo arm.

Practice Implications

While past research has suggested that long-term consumption of grape juice benefited adults with cognitive impairment, this study suggests that significant benefit can be measured in everyday tasks such as driving in healthy but stressed individuals.
The benefits appeared to persist even when the study participants were no longer drinking grape juice.
Eating foods rich in polyphenols such as blueberries, chocolate, and grape juice is associated with improved cognitive function in human clinical trials.1 Concord grape juice is a distinctly American food. Ephraim Bull developed the Concord grape in Concord, Massachusetts in 1849. The grape and, in particular, its juice are excellent sources of polyphenols, notably pro-anthocyanidins and anthocyanins. These flavonoids are associated with improved cognitive function, the result of both reduced neuroinflammation and increased neurogenesis and synaptic plasticity.2,3 Three- and four-month studies with older adults suffering from cognitive problems demonstrated that drinking CJC improves memory.4,5
Studies feeding blueberries to rats suggest that these benefits are the result of increased activation of cyclic adenosine monophosphate (cAMP) binding protein, which leads to increases in brain-derived neurotrophic factor in the hippocampus. Blueberries improved spatial memory in the rats.6 Consuming cocoa flavonoids has been associated with improved cerebral blood flow in humans, an effect that is probably the result of increased nitric oxide action.7,8 Functional MRI studies have demonstrated that CGJ increases cerebral blood flow in the right prefrontal and superior parietal cortical regions in both healthy and cognitively impaired adults.7 Concord grape juice is also associated with improved cardiovascular disease because it improves endothelial and nitric oxide function.9
McEwen and Stellar described the allostatic load model in 1993 to explain how environmental factors and “genetic predisposition lead to large individual differences in susceptibility to stress and, in some cases, to disease.”10 This allostatic load model is often described as chronic wear and tear on the body.
Cognitive impairment is often explained by employing this allostatic load model; chronic stress, cardiovascular disease, and other risk factors trigger a cascade of physiologic and psychological consequences that include decreased cognitive capability.11
Thus the authors of this current study hypothesized that individuals with higher levels of daily stress might be more likely to experience benefit from the effects of high-dose polyphenols in CGJ. Such a benefit had already been demonstrated in female rats.12
The choice of working women with young children to be study participants might be considered either amusing or perhaps insulting.
While the cognitive testing performed on these women provided objective quantitative measurements, it is the test of driving skill that is most revealing and easiest to comprehend.
Driving is a complex skill that requires many different cognitive functions to interact smoothly and quickly. It will come as no surprise that stressed people make more driving errors.13 The finding that drinking grape juice had a significant lasting effect on both cognitive function and driving performance is logical but it is still impressive.
Drinking CJC was associated with statistically significant improvements in verbal recall, spatial recall, psychomotor skills, and executive function. These assessments also report that during the CGJ phase of the study, participants were significantly more contented, alert and reported being less stressed. Scores on the driving performance tests improved significantly during arm 1 of the study but interestingly were as dramatic during arm 2 when participants received placebo instead of CGJ. Even though a month had passed, it appears that the improvement in function associated with drinking grape juice persisted. This effect was greater than expected, and in future studies using a crossover design the washout period should be extended further.
Patients often become enamored with exotic fruit juices imported from distant lands and willingly pay substantial sums of money to obtain them in the hope of improving their health. This present study and other studies on common American Concord grape juice demonstrate its significant benefit. If our goal is to further the best interests of our patients, we should be encouraging them to choose common grape juice rather than juices from more exotic locales, at least until common grape juice is shown to be inferior.

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