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Study: Coffee Consumption Linked to Shifts in Gut Microbiome and Changes in Mood, Cognition Among 62 Adults

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Coffee's Impact on the Gut and Mind: A New Study

A study from APC Microbiome Ireland examines how habitual coffee intake influences the gut microbiome and psychological well-being, revealing effects both dependent on and independent of caffeine.

Researchers at APC Microbiome Ireland, University College Cork, published a study in Nature Communications examining the relationship between habitual coffee intake, the gut microbiome, and psychological measures. The study was sponsored by the Institute for Scientific Information on Coffee.

Participants and Methodology

The study involved 62 healthy adults aged 30–50 in Ireland. The cohort included 31 individuals who regularly consumed 3–5 cups of coffee per day (classified as moderate drinkers by the European Food Safety Authority) and 31 individuals who did not drink coffee. The non-coffee drinkers provided baseline data only.

The regular coffee drinkers underwent a structured intervention:

  • Phase 1: A two-week period of complete coffee abstinence.
  • Phase 2: A three-week period during which coffee was reintroduced. Participants were randomly assigned to receive either caffeinated coffee (n=16) or decaffeinated coffee (n=15) on a blinded basis.

Measurements included psychological assessments, cognitive tasks, dietary logs, and biological samples (blood, stool, and urine) collected at various points.

Findings on Gut Microbiome

Analysis of fecal samples indicated that coffee consumption was associated with changes in the gut microbiota composition, irrespective of the caffeine content.

Specific bacterial populations reported to be increased in coffee drinkers compared to non-drinkers included:

  • Eggertella sp. (associated with gastric and intestinal acid secretion)
  • Cryptobacterium curtum (involved in bile acid synthesis)
  • Certain Firmicutes species

Urinary and fecal metabolite profiles were also altered, showing increases in caffeine metabolites and phenolic compounds.

Findings on Mood and Cognition

The study reported several associations between coffee intake and psychological measures, with some effects dependent on caffeine content and others not.

Both caffeinated and decaffeinated coffee:

Consumption was associated with lower scores for perceived stress, depression, and impulsivity compared to the abstinence period.

Caffeinated coffee:

Reintroduction was associated with reduced feelings of anxiety, reduced cortisol levels, and improvements in vigilance and attention. It was also linked to lower inflammatory markers (IL-10, IL-6).

Decaffeinated coffee:

Reintroduction was associated with improvements in learning and episodic memory, improved sleep quality, and increased physical activity. It was linked to increased inflammatory markers (CRP, TNFα).

Coffee abstinence in regular drinkers:

The two-week withdrawal period was associated with reduced impulsivity and emotional reactivity compared to baseline.

Non-coffee drinkers:

This group exhibited lower baseline impulsivity and emotional reactivity compared to regular drinkers at the start of the study.

Reported Limitations

The study authors and the Institute for Scientific Information on Coffee noted several limitations:

  • The sample size of 62 participants may not be representative of broader, diverse populations.
  • The study relied on self-reported data from dietary logs and psychological questionnaires, which carries a risk of memory errors or reporting bias.
  • The study did not control for dietary additives (e.g., sugar, dairy) that participants may have added to their coffee, which could independently affect gut health and study outcomes.