Reviewed: Lamport DJ, Christodoulou E, Achilleos C. Beneficial effects of dark chocolate for episodic memory in healthy young adults: A parallel-groups acute intervention with a white chocolate control. Nutrients. February 14, 2020;12(2):483. doi: 10.3390/nu12020483.
Flavonoids and flavonoid-rich foods are associated with various health benefits. In particular, the consumption of cocoa (Theobroma cacao, Malvaceae) flavonoids is reported to benefit cardiovascular health and cognitive function. These authors conducted a parallel-group, acute intervention trial to compare the effects of dark chocolate (DC) and white chocolate (WC) on episodic verbal memory and mood in healthy young adults.
The study was conducted at the University of Reading School of Psychology and Clinical Language Sciences in Reading, United Kingdom, and included 57 females and 41 males recruited from the university student population through posters and online notices. Forty-nine participants were assigned “according to a predetermined alternating order” to one of two groups to consume either DC or WC bars (Green and Black’s; London, UK) that were matched for calories (203 kcal) and weight (35 g). The DC contained 70% cocoa; its specific flavonoid content was not assessed. Based on analyses of DC from other peer-reviewed studies, the authors estimated that the DC bar used in their study contained 83 mg flavonoids (assuming 100 mg of DC contains 237 mg total flavonoids). WC does not contain flavonoids.
Outcome measures were assessed at baseline before the participants ate the chocolate and two hours afterward. The Rey Auditory Verbal Learning Test (RAVLT) tool was used to measure episodic memory. For the RAVLT, subjects listened to a list of 15 nouns and, immediately after, were asked to recall as many words as possible; this process was repeated four additional times using the same words. Next, the subjects listened to an “interference” list of 15 different nouns and, immediately after, were asked to recall as many of the new words as possible. After a 20-minute delay, subjects were then asked to recall words from the first list. RAVLT scores included immediate word span, words learned, final acquisition, total acquisition, proactive interference, retroactive interference, delayed recall, and total recall. The authors noted the fact that all subjects were enrolled in a university degree program “enabled control over educational attainment, which is a predictor of episodic memory performance.”
Subjective mood was assessed using two self-report measures: the Positive and Negative Affect Schedule (with higher scores representing higher levels of affect) and the Bond-Lader scale, which assessess alertness, contentment, and anxiety (with higher scores indicating higher levels of each variable).
Upon arriving at the test site, during session one, participants were measured for height and weight, completed the outcome assessments, and then ate their assigned chocolate. They returned to the laboratory two hours later after fasting and completed the outcome assessments for a second time. Laboratory conditions remained consistent during the trial.
Two hours after consumption of the chocolate, greater improvements in RAVLT scores were observed in the DC group compared to the WC group for immediate word span, words learned, final acquisition, total acquisition, delayed recall, and total recall (Table 1). These results indicate an increased ability to learn words initially and throughout the task. A lack of any effect on interference in the DC group suggests that the DC did not reduce the process of forgetting caused by learning new words or reduce the effect of old learning on new learning.
No significant effects were observed for the subjective mood outcomes. Positive affect (the extent to which one experiences positive emotions and interactions) and anxiety increased and negative affect decreased in both groups from baseline to two hours after chocolate consumption. The authors note that the reported anxiety may be related to anxious feelings associated with anticipating performing the RAVLT.
The authors suggested that an increase in cerebral blood flow following the consumption of flavonoid-rich cocoa, which has been observed in other studies, may be a possible mechanism of action for the episodic memory improvements seen after two hours in the DC group.
A limitation of this study is that sensory properties, such as taste and pleasure, may have affected the cognitive effects; however, the authors state this is somewhat countered by the lack of differences in positive and negative affect between the two groups. Another limitation is the lack of assessment of lifestyle factors (e.g., sleep quality, diet, and physical activity) and hormonal variations, which could have contributed to differences in cognitive function. The study is further limited by the fact that the flavonoid content of the DC was not measured.
The authors conclude that “70% cocoa dark chocolate consumption appears to benefit verbal episodic memory two hours post consumption in healthy young adults relative to a white chocolate control. These findings support the notion that everyday available portions (35 g) of dark chocolate might confer benefits to the brain in healthy consumers.”