If you feel that your morning coffee puts a spring in your step, science agrees. In the first large-scale real-world study of its kind, researchers have found that caffeine isn't just a stimulant but can significantly improve mood under certain conditions – especially in the morning.
In an international study led by Germany's Bielefeld University, researchers investigated the real-world impact of caffeine – in the form of coffee – on emotions. Over two separate studies, 236 adults aged 18 to 29 logged their mood and caffeine intake multiple times per day over two to four weeks. All up, the team gathered more than 23,000 datapoints over the two studies.
"Around 80% of adults worldwide consume caffeinated beverages, and the use of such stimulating substances dates far back in human history," said senior author Sakari Lemola, a professor at Bielefeld University. "Even wild animals consume caffeine; bees and bumblebees prefer nectar from plants that contain caffeine.’
The observational studies used Experience Sampling Methodology (ESM) to capture real-time data about participants' thoughts, behaviors and emotions in their natural environment, rather than traditional lab-based experiments. Together, 115 participants aged 18 to 25 and 121 individuals aged 18 to 29 were studied for 14 and 28 days, respectively. While going about their normal daily lives, they were prompted to complete surveys regarding caffeine consumption, current emotional state, tiredness levels, social context (alone or having coffee with others), and whether it was a workday or not. They received up to seven time-randomized app prompts from morning to night.
The scientists had already collected data on the participants’ typical daily coffee intake, caffeine dependency, sleep quality (as per the Pittsburgh Sleep Quality Index) and symptoms of depression and anxiety (using screening tools PHQ-9 and GAD-7). Sleep duration and midpoint were calculated daily with sleep diaries. Intake was assessed by asking participants whether they had consumed any caffeinated drinks in the previous 90 minutes, and were required to report their feelings of happiness, enthusiasm, and contentment (positive), as well as sadness, worry and upset (negative).
What they found was that participants had a noticeable mood boost following coffee, but this effect was strongest within 150 minutes of waking up. After that, the positivity faded, only picking up slightly again in the evening. Not surprisingly, this link between caffeine and good mood was greater when people were tired, but less pronounced when they were drinking coffee in social situations.
"Caffeine works by blocking adenosine receptors, which can increase dopamine activity in key brain regions – an effect that studies have linked to improved mood and greater alertness," said Professor Anu Realo from the University of Warwick.
By contrast, caffeine didn’t consistently reduce negative moods, and some – like "worry" – remained unchanged altogether. The researchers believe this could be the nature of the emotion, where participants who were worried potentially had more deeper, long-term concerns that a stimulant like caffeine may not affect. Still, the feel-good impact of a cup of coffee was consistent across the study population.
"We were somewhat surprised to find no differences between individuals with varying levels of caffeine consumption or differing degrees of depressive symptoms, anxiety, or sleep problems," said Justin Hachenberger from Bielefeld University. "The links between caffeine intake and positive or negative emotions were fairly consistent across all groups."
The researchers expected that more anxious people would in turn experience a greater degree of negative mood shifts, such as increased nervousness, after their coffee. (However, Hachenberger added that people who have bad reactions to coffee would probably avoid it – and the study did not include those who abstained from caffeine.)
The researchers also pointed out that the study's depression and anxiety measures were not based on clinical diagnoses, and no caffeine-withdrawal data was taken. They also noted that the strength of the results could have been bolstered with additional data – such as including participants' chronotypes to assess natural circadian rhythms, which may have offered more insight into the power of the morning coffee for some people.
Still, the research is among the most detailed real-world investigations into caffeine and mood to date. And it offers new insight into how timing and tiredness influence coffee's emotional effects, and suggests the ritual of a morning cup might have a real psychological impact – especially when it comes to starting the day in a positive mindset.
"This study provides evidence that caffeine consumption is associated with increases in momentary positive affect in everyday life, with effects being particularly pronounced shortly after waking up (i.e., in the morning)," the researchers concluded. "However, the relationship between caffeine and affect was not moderated by individual differences in caffeine sensitivity, but rather by factors such as tiredness and social context."
The research was published in the journal Scientific Reports.
Source: Bielefeld University
