Recent research suggests that the consumption of caffeinated beverages is linked to a measurable increase in positive feelings, particularly during the morning hours. While caffeine reliably lifts spirits, its ability to reduce negative emotions appears less consistent and does not depend on the time of day. These findings were detailed in a paper published in the journal Scientific Reports.

Caffeine is the most widely consumed psychoactive substance in the world. Estimates suggest that nearly 80 percent of the global population ingests it in some form. Common sources include coffee, tea, soda, and chocolate. Consumers often rely on these products to combat fatigue or improve their focus. Many also anecdotally report that a cup of coffee improves their general disposition.

Researchers have studied the effects of caffeine extensively in laboratory settings. These controlled environments have confirmed that the substance acts as a stimulant for the central nervous system. However, laboratories are artificial environments. They strip away the messy variables of daily life. They cannot easily account for social interactions, work stress, or the natural fluctuations of the biological clock.

Justin Hachenberger, a researcher at Bielefeld University in Germany, led a team to investigate these effects in the real world. The team sought to understand how caffeine interacts with an individual’s emotional state outside of the laboratory. They also wanted to see if factors like the time of day or social setting changed the outcome.

To understand the study, it is helpful to distinguish between “mood” and “affect.” In psychology, mood typically refers to a sustained emotional state that lasts for a long period. Affect refers to short-term, reactive emotional states. These are the immediate feelings a person experiences in response to a stimulus. The researchers focused specifically on momentary affect.

The biological mechanism behind caffeine is well understood. The substance acts as an adenosine antagonist. Adenosine is a chemical that accumulates in the brain throughout the day. It binds to specific receptors and slows down nerve cell activity. This process creates the sensation of drowsiness.

Caffeine mimics the shape of adenosine. It binds to the same receptors but does not activate them. This blocks the real adenosine from doing its job. By preventing this slowdown, caffeine allows stimulating neurotransmitters like dopamine to remain active. This leads to increased alertness and potentially improved feelings of well-being.

The researchers employed a technique known as the Experience Sampling Method. This approach involves asking participants to report on their experiences repeatedly throughout the day in their natural environments. This method reduces memory errors. Participants report what they are feeling right now rather than what they remember feeling yesterday.

The investigation consisted of two separate studies involving young adults. The first study tracked 115 participants for two weeks. The second tracked 121 participants for four weeks. Participants ranged in age from 18 to 29. They used smartphones to answer short surveys seven times a day.

In each survey, participants reported whether they had consumed any caffeinated beverages in the past 90 minutes. They also rated their current feelings. They used a sliding scale to indicate how enthusiastic, happy, or content they felt. These items combined to form a score for positive affect. They also rated how sad, upset, or worried they felt. These items formed a score for negative affect.

The data showed a clear association between caffeine and positive feelings. In both studies, participants reported higher levels of enthusiasm and happiness after consuming caffeine. The statistical analysis accounted for sleep duration and sleep quality. This suggests the mood boost was not simply a result of being well-rested.

The timing of consumption played a major role in the intensity of this effect. The association between caffeine and positive affect was strongest in the first few hours after waking up. Specifically, the boost was most pronounced within 2.5 hours of rising.

This morning peak aligns with the concept of sleep inertia. This is the groggy transition period between sleep and full wakefulness. The researchers propose that caffeine may help individuals overcome this state more effectively. It helps jump-start the sympathetic nervous system. As the day progressed, the link between caffeine and positive feelings weakened.

The results regarding negative affect were different. The researchers hypothesized that caffeine would reduce feelings of sadness or worry. The data only partially supported this. A reduction in negative affect was observed in the second, longer study. It was not observed in the first study.

Unlike positive feelings, the reduction in negative feelings did not change based on the time of day. If caffeine helped mitigate sadness, it did so regardless of whether it was morning or evening. This suggests that the mechanisms driving positive and negative affect may differ.

The study also examined whether the context of consumption mattered. The researchers looked at whether participants were alone or with others. They also asked about levels of tiredness.

Tiredness acted as a moderator for the effect. Participants who felt more tired than usual experienced a greater increase in positive affect after consuming caffeine. This supports the common use of caffeine as a countermeasure against fatigue.

Social context also influenced the results. The link between caffeine and positive affect was weaker when participants were around other people. This finding is somewhat counterintuitive. One might expect socializing over coffee to boost mood further.

The authors suggest a “ceiling effect” might be at play. Social interaction often increases positive affect on its own. If a person is already feeling good because they are with friends, caffeine may not be able to push their positive feelings much higher. The chemical effect becomes less noticeable amidst the social stimulation.

The researchers also looked for differences based on individual traits. They collected data on participants’ habitual caffeine intake. They also screened for symptoms of anxiety and depression using standardized questionnaires.

Surprisingly, these individual differences did not alter the results. The relationship between caffeine and mood remained consistent across the board. Frequent consumers did not show a different pattern of emotional response compared to lighter users.

This challenges the “withdrawal reversal” hypothesis. Some scientists argue that caffeine only makes people feel better because it cures withdrawal symptoms. If that were the only factor, heavy users would experience a massive boost while light users would feel little. The consistency across groups suggests there may be a direct mood-enhancing effect beyond just fixing withdrawal.

Hachenberger noted this consistency in the press materials. He stated, ‘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. The links between caffeine intake and positive or negative emotions were fairly consistent across all groups.’

However, there are caveats to consider. The study relied on self-reports. While the sampling method is robust, it still depends on participant honesty and accuracy. The sample consisted entirely of young adults. The way an 18-year-old metabolizes caffeine may differ from that of an older adult.

Additionally, the study is observational. It shows a correlation but cannot prove causation. It is possible that people who are already in a good mood are more likely to seek out coffee. However, the use of within-person analysis helps control for this to some degree.

There is also the question of anxiety. High doses of caffeine can induce jitteriness and anxiety. The study did not find a link between caffeine and increased worry. However, the researchers note that individuals prone to caffeine-induced anxiety might avoid the substance entirely. These people would naturally exclude themselves from a study on caffeine consumption.

The researchers recommend future studies use more objective measures. Wearable technology could track heart rate and skin temperature. This would provide precise physiological data to match the psychological reports. Tracking the exact moment of consumption, rather than a 90-minute window, would also improve precision.

Understanding these daily fluctuations helps paint a clearer picture of human behavior. It moves the science of nutrition and psychology out of the lab and into the rhythm of daily life. For now, the data supports the habit of the morning coffee. It appears to be an effective tool for boosting positive engagement with the day, particularly in those first groggy hours.

The study, “The association of caffeine consumption with positive affect but not with negative affect changes across the day,” was authored by Justin Hachenberger, Yu-Mei Li, Anu Realo, and Sakari Lemola.