Quitting coffee for just two weeks may make people less impulsive and less stressed, and switching to decaf could improve sleep and memory, a study suggests.
Scientists tracked 62 healthy adults to examine how coffee affects the body and brain. The group included 31 regular coffee drinkers and 31 people who did not drink coffee.
At the start of the study, all volunteers gave blood, urine and stool samples.
They also completed questionnaires on mood and behavior, as well as memory and cognitive tests.
The regular coffee drinkers were then told to stop drinking coffee entirely for two weeks. After that, they were randomly assigned either caffeinated coffee or decaf for a further 21 days. Sixteen received caffeinated coffee and 15 were given decaf.
Researchers then compared how participants changed during the withdrawal and re-introduction phases.
They found regular coffee drinkers experienced more impulsive behaviour and emotional reactivity than people who did not drink coffee.
But after coffee drinkers gave up their habit for a fortnight, both measures fell.
Quitting coffee for just two weeks may make people less impulsive and less stressed, while switching to decaf could improve sleep and memory, a study suggests
When coffee was re-introduced, the effects differed depending on the type consumed.
Participants given caffeinated coffee reported lower anxiety and psychological distress.
Those assigned decaf saw improvements in sleep quality, physical activity and memory scores.
Researchers said the findings suggest coffee may affect the body in ways that go well beyond the caffeine hit many drinkers rely on each morning.
The study, published this week in Nature Communications, was led by researchers at University College Cork in Ireland.
Alongside the behavioural findings, scientists also discovered that regular coffee drinkers had a distinctly different gut microbiome from non-drinkers.
The gut microbiome refers to the trillions of bacteria and other microbes living in the digestive system. Scientists increasingly believe it may help shape digestion, immunity, metabolism, mood and even brain health.
Some of the bacterial patterns seen in coffee drinkers began to shift back towards levels seen in non-drinkers after the two-week withdrawal period.
When coffee was re-introduced, both caffeinated and decaffeinated versions triggered fresh bacterial changes.
The team said this suggests some of coffee’s effects may come from naturally occurring plant compounds rather than caffeine alone.
These substances, known as phenolic acids, are antioxidants also found in fruit, vegetables and other plant foods.
Researchers also found signs coffee could influence inflammation.
At the start of the trial, regular coffee drinkers had lower levels of C-reactive protein, a common marker linked to inflammation in the body.
They also had higher levels of IL-10, an anti-inflammatory molecule.
When coffee was withdrawn, some inflammatory markers rose.
After coffee was reintroduced, both the caffeinated and decaf groups showed a reduced inflammatory response in laboratory testing.
However, the researchers stressed the study does not prove coffee directly causes better health, improved memory or changes in personality.
The trial was relatively small, involving only 62 people.
Some of the gains seen in memory tests may simply have reflected participants becoming more familiar with repeating the same tasks.
The authors also said the sample lacked sufficient diversity and may not have been large enough to detect more subtle effects.
Previous studies have linked moderate coffee intake to lower risks of type 2 diabetes, liver disease and some heart conditions.
But coffee can also worsen anxiety, palpitations and poor sleep in sensitive people, particularly when consumed in large amounts or late in the day.
The researchers said larger studies are now needed to confirm whether the microbial changes seen in coffee drinkers translate into meaningful long-term health benefits.
