Study Examines Coffee's Effects on Gut Microbiome and Mood

Researchers at APC Microbiome Ireland, University College Cork, investigated the relationship between habitual coffee consumption and the microbiota–gut–brain axis. The findings were published in Nature Communications.

Study Design

The study involved 62 healthy adults in Ireland, aged 30–50. The participant group included 31 moderate coffee drinkers (defined as consuming 3–5 cups daily) and 31 non-coffee drinkers. The European Food Safety Authority considers 3–5 cups per day a safe level of consumption.

The research was conducted in two phases:

• For two weeks, all participants abstained from coffee, providing regular psychological assessments and stool, blood, and urine samples.
• Coffee was then reintroduced to the former drinkers on a blinded basis. Half received caffeinated coffee and half received decaffeinated coffee for three weeks.

Key Findings

Both caffeinated and decaffeinated coffee consumption was associated with lower reported levels of perceived stress, depression, and impulsivity.

• Caffeinated coffee was associated with reduced anxiety, improved vigilance and attention.
• Decaffeinated coffee was associated with improved learning and episodic memory, as well as better sleep and increased physical activity.

Coffee consumption was associated with increased levels of specific bacteria compared to non-coffee drinkers, including:

• Eggertella sp., associated with gastric and intestinal acid secretion
• Cryptobacterium curtum, involved in bile acid synthesis
• Firmicutes, associated with positive emotions in females

Coffee consumption altered fecal and urinary metabolite profiles, including increased caffeine metabolites and phenolic compounds.

• Caffeinated coffee was associated with lower inflammatory markers IL-10 and IL-6.
• Decaffeinated coffee was associated with higher levels of CRP and TNFα.

Conflicting Observations

The study reported two contrasting findings regarding anxiety:

• Caffeinated coffee consumption was associated with reduced feelings of anxiety according to one measurement.
• Coffee abstinence in regular drinkers was associated with reduced impulsivity and emotional reactivity, while reintroduction of caffeinated coffee improved cognitive performance.

Researchers' Statements

Professor John Cryan, the corresponding author, stated: "Our findings reveal the microbiome and neurological responses to coffee, as well as their potential long-term benefits for a healthier microbiome. Coffee may modify what microbes do collectively, and what metabolites they use."

Cryan added: "Coffee is more than just caffeine — it's a complex dietary factor that interacts with our gut microbes, our metabolism, and even our emotional wellbeing."

Background and Limitations

The study was supported by the Institute for Scientific Information on Coffee (ISIC).

Researchers noted the following limitations:

• The small sample size may not represent diverse global populations.
• The study relied on self-reported data, which carries risks of memory errors and bias.
• The study did not control for dietary additives like sugar or dairy, which could independently affect gut health.