A new study evaluating the popular hot beverage’s impact on mental health found that while drinking tea was unrelated to mood, drinking coffee may be associated with reducing overall symptoms of depression. The study, published in Scientific Reports, analyzed the daily drinking habits of nearly 2,000 adults to understand how these beverages align with psychological well-being.
Mental health conditions affect millions of people around the world, often interfering with daily life and making it difficult to maintain a normal daily routine. Depression involves persistent low mood, deep sadness, and loss of interest in typical activities. Anxiety manifests as overwhelming worry and nervous tension that feels out of control.
Rates of both psychological conditions are increasing in many regions of the world, including the Middle East. Medical professionals treat these symptoms using a variety of behavioral treatments and prescription medications. Researchers also hope to identify factors in daily life that may prevent these symptoms from developing in the first place.
Nutrition is a prime target for scientists studying modifiable health habits. The foods and drinks that people consume every day provide the cellular building blocks for brain chemicals that regulate mood. Coffee and tea are two of the most widely consumed beverages on the planet, so nutritionists want to know if they have mental health benefits.
Previous research on coffee and tea has yielded mixed results. Several scientific papers report that drinking these drinks reduces the odds of depression. Other studies suggest they worsen mental health symptoms or have no effect at all.
These inconsistent results may be due to differences in the way drinks are made and consumed in different cultures. Much of the existing research originates from Western countries and East Asia. There remains relatively little research specifically focused on people in the Middle East.
Tea is traditionally the main daily beverage in Iran and is deeply integrated into the local culture. Although coffee has become increasingly popular over the past decade, total consumption remains low compared to the United States and Europe. This unique cultural shift creates an ideal environment to observe how these two different drinking habits respond to psychological distress.
Mohammad Matin Majulian, a researcher at Tehran University of Medical Sciences, led a team investigating this very topic. The researchers wanted to isolate the dietary patterns of Iranian adults and compare them to self-reported mental health scores.
The researchers conducted a cross-sectional study. This type of study takes an informational snapshot of a specific population at a single point in time. The study involved 1,994 adults recruited from a large health project across five major cities across Iran.
The main objective was to collect detailed information about what these people ate and drank in the previous year. To accomplish this, a trained interviewer met with each participant and completed a questionnaire regarding special diets. The survey listed more than 100 foods and asked participants to estimate how often they eat them, as well as their typical portion sizes.
Scientists divided participants into separate categories depending on their answers. For tea, participants were divided into three groups based on their daily intake: less than 1 cup, 1 to 2 cups, or 2 or more cups. Coffee drinkers were divided more simply into those who drank at least one cup a day and those who never drank coffee.
To measure psychological well-being, the team used a translated and validated mental health questionnaire. Participants answered a series of questions and ranked their emotional state on a simple numerical scale. Higher scores indicated more depressive or anxiety symptoms were present.
When analyzing the raw numbers, differences between the beverage drinking groups quickly became apparent. An initial look at the data showed no clear variation in mood scores by tea category. Those who drank many cups of tea experienced depression and anxiety at exactly the same rate as those who drank very little.
Coffee consumption showed a different picture in unadjusted data. Researchers found that people who drank at least one cup of coffee a day were 40 percent less likely to report symptoms of depression than those who didn’t drink coffee. They were also 27% less likely to experience high anxiety.
In population science, initial associations don’t tell the whole story. Coffee drinkers often lead different lives than non-coffee drinkers. Survey responses found that coffee consumers in this particular region tend to be more physically active, have a higher level of education, and have more economic resources.
These external variables are known as confounders because they can falsely create or mask a mathematical relationship between two elements. For example, the real reason people feel less depressed may not be their morning coffee habits, but their higher incomes. To find the individual effects of the drinks, the scientists adjusted the equation to remove the effects of these confounding factors.
The researchers applied several layers of statistical adjustment. They controlled for age, gender, total daily calories, smoking status, and physical activity. We also took into account certain nutrients known to support brain health, including folate, iron, magnesium, zinc, and vitamin B12.
When the team took into account all these dietary and lifestyle factors, the initial findings changed significantly. There was no association between tea and mood. When focusing on coffee, conditioning completely erased the association with reduced anxiety.
The mathematical association between coffee and reduced depression was similarly weakened. Finally, the adjusted results were also not statistically significant for depression. Rather than showing a definitive protective effect, this calculation only showed a subtle trend that coffee drinkers may have slightly fewer symptoms of depression.
Although the final numbers only hinted at subtle trends, scientists have several biological theories as to why coffee affects mood over time. The main active ingredient in coffee is caffeine. Caffeine is an active chemical molecule that easily travels from the bloodstream directly to the brain.
Once in the brain, caffeine binds to specific structures on the surface of brain cells known as adenosine receptors. Under typical conditions, a molecule called adenosine matches up with these receptors throughout the day. When adenosine binds, it signals the nervous system to slow down, making a person feel sleepy and relaxed.
Caffeine blocks this process by taking away the adenosine spot without causing fatigue signals. Caffeine essentially releases the brakes on your nervous system by blocking adenosine. This increases the activity of other naturally occurring brain chemicals.
Two of the signaling chemicals that increase in the presence of caffeine are dopamine and norepinephrine. Dopamine is deeply involved in human motivation, reward, and the experience of pleasure. Increased dopamine activity is one way the brain lifts a person’s mood and combats feelings of sadness.
Noradrenaline acts similarly to adrenaline, increasing a person’s overall alertness and physical concentration. The simultaneous increase in both dopamine and norepinephrine gives coffee drinkers that characteristic morning refreshment. In the short term, this chemical cascade acts as a calm mood enhancer.
The long-term effects of daily caffeine use are quite different. This may explain why population studies rarely show significant mental health benefits for heavy drinkers. The human body is extremely adaptable. When caffeine regularly blocks normal sleepiness signals, the brain attempts to restore resting balance.
To compensate for the blockage, the brain produces entirely new adenosine receptors. With more receptors available, more caffeine is required to achieve the exact same stimulation result. This physiological adaptation is medically known as tolerance.
Regular coffee drinkers have developed a tolerance, so their daily habit may simply cause their mood to return to baseline, rather than continually raising it above normal levels. When you skip your daily cup, your newly abundant adenosine receptors remain fully open, resulting in sluggishness and irritability. This biological cycle helps explain the different results seen in large-scale dietary studies over long periods of time.
Another relevant biological factor involves genetics. Every person has a slightly different genetic code, which determines how quickly their internal organs process and remove molecules from the bloodstream. Some people metabolize caffeine rapidly and experience short, pleasant bursts of energy.
Some people have slow metabolisms. For them, caffeine remains in the body for hours on end. You are more likely to experience nervousness, insomnia, and increased heart rate. Over time, these negative physical reactions can contribute to psychological distress and completely negate the initial mood improvement.
While the Iranian study provides a useful examination of a unique population, the authors emphasized that their study has several limitations. The most notable weakness is the cross-sectional study design. Evaluating people at a single moment in history makes it impossible to determine the true direction of relationships.
For example, scientists cannot say whether drinking coffee directly prevents depression. The opposite scenario is possible as well. People who suffer from clinical depression may naturally lose the physical motivation to prepare their morning coffee or avoid drinks that cause general anxiety.
Reliance on human memory also poses research challenges. Participants had to think back over a year to estimate their average food and drink intake. Relying on long-term memory, people often overstate or underestimate their true habits.
The researchers also excluded people with severe chronic medical conditions, such as kidney disease, liver damage, or extreme immune system abnormalities. Excluding these patients helped isolate the effects of diet itself, but it also meant that the population studied was generally healthier than average. The final numbers may not apply to people suffering from severe physical illness.
Finally, the actual number of regular coffee drinkers found in this study was relatively small. Of the approximately 2,000 total participants, only 348 consumed coffee daily. Small group sizes limit the mathematical ability of statistical software to detect subtle health relationships.
To build this foundation, researchers need to design prospective cohort studies. In prospective cohorts, scientists recruit large groups of healthy volunteers and continuously track their health habits over many years. By monitoring changes in health conditions over time, researchers can more accurately chart a timeline of cause and effect in humans.
The study was authored by Mohammad Matin Majulian, Ghazaleh Bahrami, Noushin Mohammadifard, Fahimeh Hagighatdoost, Farid Najafi, Hossein Farshidi, Masoud Lotfizadeh, Touba Kazemi, Hamidreza Rohafza and Nizar Sarafzadegan.
