Scientists talked about the effect of coffee on the gut microbiome and cognitive functions

Regular coffee consumption changes the composition of the intestinal microbiota, increases impulsivity and emotional reactivity, while avoiding the drink improves memory and reduces anxiety. This conclusion was reached by scientists at University College Cork, who published the results of a large-scale study in the journal Nature.

The experiment involved 62 healthy adults aged 30 to 50 years old living in Ireland. 31 of them regularly consumed coffee — from three to five cups a day — while the rest did not drink it at all. At the first stage, the scientists compared the two groups in terms of baseline health indicators, cognitive functions, and microbiome composition.

Then coffee lovers completely abandoned the drink for two weeks, after which they were divided into two subgroups: one resumed drinking caffeinated coffee, the other switched to a decaffeinated version for three weeks. Throughout the study, participants took stool, blood, urine, and saliva samples, underwent cognitive tests, and filled out psychological questionnaires. The diet of the subjects was recorded using seven-day food diaries: there were no significant differences in nutrition between the groups.

Coffee drinkers showed significantly higher rates of impulsivity on the UPPS-P scale and emotional reactivity on the ERS scale compared to those who did not drink the drink. The authors found that quitting coffee reduced both indicators — participants became less impulsive and more emotionally stable already during the two-week abstinence period.

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However, some of the improvements turned out to be specific to a particular type of drink. Resuming caffeinated coffee consumption reduced anxiety and psychological distress, as well as improved attention scores in the PASAT test. Decaffeinated coffee, on the other hand, had a positive effect on sleep quality, physical activity, and episodic memory.

Participants from this subgroup showed a significant improvement in their results on the ModRey test and a reduction in the number of errors in the PAL associative learning task. The researchers suggested that a similar effect may be associated with improved sleep and increased physical activity, factors that, according to available data, directly support memory functions.

The intestinal microbiome of coffee drinkers was characterized by an increased content of bacteria of the species Cryptobacterium curtum and Eggerthella, while non-coffee drinkers had more Veillonella parvula and Haemophilus parainfluenzae. The alpha diversity of the microbiota differed between the groups, but during the experiment itself, when coffee was discontinued and re-introduced, the overall diversity did not change significantly. This indicates that coffee affects specific strains rather than the microbial community as a whole.

Concentrations of indole-3-propionic acid, indole-3-carboxaldehyde, and the neurotransmitter gamma-aminobutyric acid (GABA) were significantly reduced in the feces of coffee drinkers. All three compounds are synthesized by intestinal bacteria and are involved in the regulation of intestinal and brain functions. The integration of microbial, metabolic, and cognitive data allowed the authors to identify nine key metabolites: theophylline, caffeine, and a number of phenolic acids that are most closely related to both microbiota composition and cognitive performance.

Coffee drinkers had lower blood levels of C-reactive protein (CRP), a marker of inflammation, and higher levels of anti—inflammatory interleukin-10. Refusal of the drink, on the contrary, was accompanied by an increase in CRP and tumor necrosis factor (TNF-α), which indirectly indicates the protective role of coffee against chronic inflammation. Both caffeine and the decaffeinated version reduced the production of interleukin-6 upon stimulation of immune cells, which indicates the involvement of non-caffeinated components of the drink in modulating the immune response.

The authors emphasize that non—coffee drinkers have a number of systemic advantages - lower impulsivity, better cognitive stability, and the absence of caffeine withdrawal symptoms, which may be related to the preservation of endogenous neurophysiological rhythms.

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