A daily cup of coffee may do more than wake you up, according to a small study from University College Cork in Ireland. Researchers found that both caffeinated and decaffeinated coffee were linked to changes in gut microbes and to some measures of mood. The two types also appeared to affect cognition differently.
The study followed 62 healthy adults, 31 of whom were regular coffee drinkers and 31 who did not drink coffee. The regular drinkers, who typically had three to five cups a day, stopped drinking coffee for two weeks. They were then assigned to resume either caffeinated or decaffeinated coffee for three weeks. Throughout the process, the researchers tracked mood and cognitive test scores and analyzed stool and urine samples.
After coffee was reintroduced, both groups reported lower stress, depression and impulsivity than at the start of the study. The caffeinated group also reported reduced anxiety and improved on an attention test. Participants who drank decaf showed improvement on a test of episodic memory, which measures the ability to recall information and experiences. Coffee drinkers also showed differences in certain gut bacteria, and both groups showed some microbial changes after starting either type of coffee. The study, however, could not prove that gut microbes caused the reported mood or cognitive changes.
The study's corresponding author, Professor John Cryan, said coffee is more than caffeine. « 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, » Cryan said in a statement. He added that caffeinated and decaffeinated coffee may influence health « in distinct but complementary ways. » He also noted that public interest in gut health has risen sharply, and that the mechanisms behind coffee's effects on the gut-brain axis remain unclear.
Rebecca Steele, a New York-based clinical psychologist who was not involved in the research, urged caution in interpreting the results. She said people should be careful about drawing broad conclusions from a small sample. Gains on cognitive tests, she noted, do not necessarily translate into meaningful or lasting improvements in everyday life. Research has found short-term effects of caffeine on alertness, but evidence on its long-term effects on cognition remains inconclusive.
Steele also said the decaf group's memory results were interesting, but that changes in sleep and physical activity, along with a possible learning effect from taking the same tests more than once, complicate the findings. She cautioned that changes in self-reported stress and depression scores should not be taken as evidence that coffee treats clinical depression.