Blueberries induce calmness but not better cognition, sleep quality in MetS patients

Consumption of blueberries improves self-rated calmness postprandially, with significant associations seen between cognition and metabolites, among individuals with metabolic syndrome (MetS), reports a recent study. However, these data do not show substantial improvements in cognition, mood, alertness, or sleep quality.

“[W]e present the first evidence in those with MetS but without cognitive dysfunction that neither chronic nor postprandial blueberry intake was effective in improving cognition, mood, or sleep quality, with the exception of postprandial calmness,” the authors said.

This double-blind, randomized controlled trial explored the primary effect of consuming freeze-dried blueberry powder, as compared with an isocaloric placebo, on cardiometabolic health >6 months and a 24-hour postprandial period (at baseline).

A secondary analysis was also conducted. The authors presented data from participants who completed mood, alertness, cognition, and sleep assessments (n=115 in the 6-month study; n=33 in the postprandial study) using Bond-Lader self-rated scores, electronic cognitive battery (ie, testing attention, working memory, episodic memory, speed of memory retrieval, executive function, and picture recognition), and the Leeds Sleep Evaluation Questionnaire.

Finally, the authors quantified urinary and serum anthocyanin metabolites, as well as determined the apolipoprotein E genotype status.

Consumption of 1 cup of blueberries significantly improved postprandial self-rated calmness (p=0.01; q=0.04; with an 11.6-percent improvement vs baseline between 0 and 24 hours for the 1 cup group). However, other parameters on mood, sleep, and cognitive functions did not change substantially after postprandial and 6-month blueberries intervention.

In addition, microbial metabolites of anthocyanins and chlorogenic acid (ie, hydroxycinnamic acids, benzoic acids, phenylalanine derivatives, and hippuric acids) and catechin correlated with favourable chronic and postprandial memory, attention, executive function, and calmness across the 1/2- and 1-cup groups. [Am J Clin Nutr 2024;119:658-668]

Blueberry benefits

“Our results contrast with previous studies in those with cognitive impairments or subjective cognitive decline, which have shown that 3–6 months of blueberry intake improved cognitive domains, including processing speed, executive function, memory impairment, and verbal span, and everyday activities which relied on manifestations of cognition and memory functions,” the authors said. [Nutr Neurosci 2023;26:1019-1033; Nutrients 2022;14:1619; J Agric Food Chem 2010;58:3996-4000; Neurobiol Aging 2018;64:147-156]

Another study also showed how blueberry intake increased blood oxygenation level-dependent in mild cognitive impairment (in the left precentral gyrus, middle frontal gyrus, and inferior parietal lobe) during working memory load tasks, suggesting improved neuronal activation. [Nutr Neurosci 2018;21:297-305]

“In addition to existing cognitive decline potentially providing a window of intervention opportunity for benefit, the reason for these disparities may, in part, be explained by heterogeneity in study design and participant characteristics that may conceivably influence cognitive performance,” the authors said.

“We suggest that our data reinforce the increasing evidence that the benefits of blueberries are more likely to be realized in those experiencing higher cognitive loads, such as those functioning under stressful situations or performing tasks with high cognitive demands, older seniors, or those with pre-existing cognitive dysfunction, and are an ineffective strategy for cognitive function improvement in those with MetS, but without cognitive dysfunction,” they noted.