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Blueberries boost calmness but not cognition in metabolic syndrome study

In a recent study published within the American Journal of Clinical Nutrition, researchers evaluated the effect of blueberry intake on mood, alertness, and cognitive function in adults with metabolic syndrome (MetS).



MetS affects one in three adults, predisposing them to heart problems risk. It predicts diabetes development, which is recognized as a modifiable mid-life risk factor for Alzheimer’s disease. Besides, an association between MetS and cognition has been incessantly reported. Brain imaging studies have shown that MetS is related to lower grey and white matter volumes and disruptions in cerebral homeostasis.

Previously, the authors showed that blueberry intake improved cardiometabolic health in MetS subjects. Various trials have reported improvements in executive function, processing speed, memory encoding, and cognitive symptoms with blueberries. Nevertheless, postprandial cognitive response to blueberries has been assessed in healthy subjects only, and data on cognitive function and mood after chronic or postprandial intervention in individuals with MetS are lacking.

Study: Chronic and postprandial effect of blueberries on cognitive function, alertness, and mood in participants with metabolic syndrome – results from a six-month, double-blind, randomized controlled trial. Image Credit: matin / Shutterstock

Concerning the study

In the current study, researchers examined the consequences of a six-month intake of blueberries on cognitive function, alertness, and mood in adults with MetS. Subjects were obese/obese adults aged 50–75, meeting at the very least three MetS components: central adiposity, impaired fasting glucose, low levels of high-density lipoprotein (HDL) cholesterol, and hypertriglyceridemia.

Participants were randomized to one among the three groups. The intervention commenced after three weeks of dietary restrictions (low in flavonoids and anthocyanin). Participants received sachets containing freeze-dried blueberries (akin to one cup of blueberries), an isocaloric placebo, or a hybrid of each (equal to half a cup of blueberries).

The assigned product was required to be consumed daily for six months. The first consequence (change in insulin resistance) was previously reported. The present study reported findings on secondary outcomes – composite cognitive function and self-rated mood and application. These data were obtained through a battery of cognitive function tests, adapted to incorporate tests for alertness and mood. The Leeds sleep evaluation questionnaire was integrated into the test battery.

Carrier status of the apolipoprotein E (APOE) genotype was also assessed. Blueberry metabolite levels in blood and urine were evaluated. An exploratory evaluation was performed to find out the association between cognitive function and metabolites. Besides, a postprandial sub-study was undertaken at baseline to evaluate the effect of 1 cup of blueberries or placebo with a high-sugar, high-fat meal on postprandial cardiometabolic and cognitive responses.

Findings

Overall, 115 participants accomplished the six-month intervention; 37, 39, and 39 individuals were assigned to blueberry, placebo, and hybrid groups, respectively. Of those, 33 accomplished the postprandial sub-study at baseline. Participants were aged 62.8, on average, with a mean body mass index (BMI) of 31.2 kg/m2.

Subjects were predominantly male (> 67%); 24.3% were APOE4 carriers. The researchers found no significant differences in any cognitive function domain over the six months. Nonetheless, consuming (a cup of) blueberries improved the accuracy of picture recognition by 4.2%. Likewise, self-rated scores of alertness and mood didn’t differ by intervention.

Moreover, the researchers didn’t observe advantages on alertness, sleep quality, and cognitive function within the postprandial sub-study. Nonetheless, self-rated (degree of) calmness was significantly higher with the blueberry intake than placebo.

The exploratory evaluation revealed associations between metabolite changes and favorable cognition, alertness, mood, and sleep quality indices following six-month and postprandial blueberry intake. Microbial metabolites of anthocyanins and chlorogenic acid (hippuric acids, phenylalanine derivatives, benzoic acid, etc.) and catechin were related to favorable memory, calmness, and executive function.

Conclusions

Taken together, the study showed that chronic intake of blueberries (at one or half cup per day) had no profit on cognitive function, alertness, and mood in adults with MetS. For subjects who consumed a high-fat, high-sugar meal, including one cup of blueberries, didn’t meaningfully ameliorate the anticipated postprandial declines in cognition, mood, and application, aside from self-rated calmness.

Overall, the information reinforce the evidence that the good thing about blueberries could also be more likely amongst individuals with higher cognitive loads, resembling those working under stress or performing tasks requiring increased cognitive demands, older people, and people with cognitive dysfunction. Blueberry intervention was ineffective in improving cognition in MetS subjects without cognitive dysfunction.

Journal reference:

  • Curtis PJ, Van Der Velpen V, Berends L, et al. Chronic and postprandial effect of blueberries on cognitive function, alertness, and mood in participants with metabolic syndrome – results from a six-month, double-blind, randomized controlled trial. The American Journal of Clinical Nutrition. Published online February 2024:S0002916523663026, DOI: 10.1016/j.ajcnut.2023.12.006, https://www.sciencedirect.com/science/article/pii/S0002916523663026
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