New research from APC Microbiome Ireland at University College Cork, published in Nature Communications, suggests coffee may influence mood and cognition through the gut-brain axis. The study, reported by ScienceDaily, tracked 31 people who regularly drank 3-5 cups of coffee per day and 31 non-coffee drinkers, combining stool and urine samples with psychological assessments.
After two weeks without coffee, the regular drinkers showed notable changes in gut metabolites compared with non-drinkers. When they resumed coffee—either caffeinated or decaf, without knowing which—both groups reported lower perceived stress, depression, and impulsivity scores. Several bacteria, including Eggertella sp., Cryptobacterium curtum, and Firmicutes, were also more abundant in coffee drinkers.
Decaf and caffeinated coffee had different cognitive effects. Decaf was associated with better learning and memory, hinting that non-caffeine compounds such as polyphenols contribute to coffee's effects. Caffeinated coffee, in turn, was linked to reduced anxiety and improved vigilance and attention. The authors caution that the small study cannot establish a direct cause-and-effect relationship, but it offers new clues about how coffee might act through gut microbes.