You stumble into the kitchen half awake and start brewing coffee.
Before you have taken a single sip, the aroma fills the room. The morning seems more manageable.
But what just happened?
No caffeine has entered your bloodstream. The coffee hasn’t touched your lips. Yet your brain may be responding.
Could the smell of coffee alone change how you feel?
Previous studies have linked coffee aroma with shifts in mood, memory, stress, and brain activity.
But these responses were usually examined separately, leaving a question unanswered: When coffee changes how someone feels, do the brain and body respond together?
Researchers at Showa Pharmaceutical University in Japan investigated that moment. Their study, published in Nutrients, involved 20 university students aged 20 to 29.
They tracked mood, brainwaves, heart rate, and heart rate variability as volunteers sat beside freshly brewed coffee – without drinking it.
Within 5 minutes, participants reported fewer negative feelings and showed a shift in an EEG-derived index linked to relaxation. Their hearts, however, appeared unchanged.
The researchers brewed 20 grams of ground coffee with 400 milliliters of water heated to 85 °C (185 °F). They placed the drink in a glass server around 50 centimeters (20 inches) from each participant.
The volunteers sat and breathed normally as the aroma spread through the room.
Before and after this aromatic pause, participants completed a questionnaire assessing tension and anxiety, depression and dejection, anger and hostility, vigor, fatigue, and confusion.
Brain activity and heart rate were recorded using a portable headband, while heart rate variability was measured with a separate wearable device.
After 5 minutes with the coffee aroma, the participants’ mood disturbance scores had fallen.
They reported less fatigue, tension and anxiety, confusion, depression, and dejection. After adjustment for multiple statistical comparisons, reductions in fatigue, tension and anxiety, confusion, and depression and dejection remained significant.
Vigor, however, did not increase significantly. The aroma appeared to be associated less with a sudden rush of energy than with turning down the volume on negative feelings.
The researchers detected an increase in an EEG-derived “relaxation index”, calculated from the relative contributions of alpha, beta, and theta brainwave activity.
That might sound as though the participants’ brains relaxed at the first whiff of coffee. But the result needs a careful pour of caution.
Although the standardized effect size was large, the absolute increase was modest. Scientists also don’t know whether a change of this magnitude represents physiologically meaningful relaxation.
The finding therefore shows a change in a calculated EEG index, not proof that coffee aroma relaxed the brain.
Meanwhile, the heart didn’t appear to join the coffee break. Neither heart rate nor heart rate variability changed significantly.
Participants who reported the greatest mood improvements did not necessarily show the largest EEG changes. At an individual level, shifts in mood, brain activity, heart rate, and heart rate variability were not significantly correlated.
This helps answer the researchers’ original question. Mood and EEG activity may both change across a group without reflecting one coordinated response.
It isn’t difficult to imagine why coffee might influence how we feel.
Our sense of smell is closely connected to brain systems involved in emotion and memory. A familiar scent can summon a person, place, or feeling before we consciously identify it.
Coffee carries plenty of associations. Its aroma may signal morning, warmth, a break from work, a conversation with a friend, or the promise of caffeine.
A separate 2018 study found that people performed better on analytical tasks when exposed to a coffee-like scent. The smell raised their expectations of performing well, suggesting learned associations or a placebo-like effect may contribute.
That leads to the study’s biggest limitation: There was no control condition.
The researchers did not compare coffee aroma with an odor-free room, an unrelated scent, or a placebo. Consequently, they cannot determine whether coffee produced the changes.
Five minutes of quiet rest might have improved participants’ moods. They may also have become comfortable in the laboratory or expected coffee to make them feel better.
The researchers did not systematically assess how often volunteers drank coffee, whether they liked it, their familiarity with its aroma, or their smelling ability.
The sample was small and limited to young university students. Aroma concentration and environmental conditions were not systematically monitored, and the recordings came from a consumer-grade EEG device.
A larger randomized study could compare coffee with both an odor-free condition and another familiar scent while measuring participants’ coffee habits, preferences, and expectations.
Related: Coffee May Boost Your Mood And Brainpower, Even Without Caffeine
Until then, there is no reason to replace your morning cup with five minutes of hopeful sniffing.
But the next time coffee improves your day before the first sip, it may be worth wondering whether your brain has already joined the coffee break.
The study was published in Nutrients.
This article was fact-checked by Rachel Garner and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
