Coffee’s mood-boosting effects aren’t just down to caffeine

Both caffeinated and decaffeinated coffee can lead to improvements in mood and cognitive performance, possibly through their effects on the gut microbiome.

Scientists have long known that coffee can influence digestion, cognition and mood, thanks partly to interactions with gut microbes. But while most research on coffee’s effects has focused on caffeine, coffee is also one of the richest sources of polyphenols – plant-derived compounds that gut microbes convert into biologically active molecules. These metabolites have been linked to anti-inflammatory effects and may influence brain function.

To get a clearer view of these interactions, John Cryan at University College Cork in Ireland and his colleagues recruited 62 healthy participants, half of whom were regular coffee-drinkers and half of whom were non-coffee-drinkers. After an initial comparison, regular drinkers abstained from coffee for 14 days, followed by a 21-day reintroduction phase in which participants were randomly assigned to consume either caffeinated or decaffeinated coffee.

The researchers collected blood, saliva, urine and stool samples to assess physiological responses to coffee-derived compounds. They also assessed the participants’ mood, cognition, stress, sleep and behaviour.

Compared with non-coffee-drinkers, consuming caffeinated coffee was associated with lower anxiety and improved attention, whereas decaffeinated coffee was linked to improved scores in memory tests and better sleep quality. Both kinds of coffee were associated with lower ratings of stress and depression.

When coffee was removed and then reintroduced, the participants’ microbiomes changed rapidly, with both regular and decaf coffee being linked to higher levels of beneficial gut bacteria. “We were surprised by how dynamic the system is,” says Cryan.

The analysis suggests that coffee’s effects on cognitive scores are caused by polyphenols, not caffeine, since these scores correlated with the measurements of certain metabolites derived from polyphenols in the participants’ urine.

Team member Daniele Del Rio at the University of Parma, Italy, says a key next step will be to determine how different types of coffee affect the microbiome. “Not all coffee is the same: even the degree of roasting profoundly influences its chemical composition.”

Nicola Segata at the University of Trento, Italy, says the work sheds light on a relatively underexplored area, but warns against overinterpretation. “The study’s relatively small sample size may limit how broadly the results can be applied,” he says.

“This study is interesting because, by examining the effects of coffee consumption on microbiota composition, it suggests that the human gut ecosystem may have helped humans adapt relatively rapidly to different diets and environments without requiring genetic change,” says Telmo Pievani at the University of Padua, Italy.