Studies have revealed the effects of caffeine on the body
Caffeine is the most popular psychoactive substance in the world. Every day, billions of people start their morning with coffee, tea, or energy drinks to feel energized and increase concentration. But the more scientists study the effects of caffeine on the brain and body, the more difficult it becomes to answer the question: is it useful or harmful? For more information, see the Izvestia article.
How does caffeine affect the body and which drinks contain it?
Modern research shows that caffeine can actually improve attention, memory, and performance. At the same time, excessive consumption can disrupt sleep, increase anxiety, and overload the nervous system. Moreover, the effect depends not only on the dose, but also on age, genetics, and even the time of day.
Caffeine is a stimulant of the central nervous system. Its main effect is related to the blocking of adenosine— a substance that is responsible for the feeling of fatigue and drowsiness. When the adenosine receptors are blocked, the brain begins to work more actively: concentration increases, reaction speeds up, and the feeling of fatigue temporarily decreases.
The researchers note that caffeine is not only found in coffee. It can be found in tea, energy drinks, soda, chocolate, and even some medications. According to the University of Montreal, caffeine remains one of the most common psychoactive substances in the world. At the same time, different drinks affect the body in different ways. For example, tea usually contains less caffeine than coffee, and is also rich in L-theanine, an amino acid that partially mitigates the stimulating effect. Therefore, tea causes a softer and longer-lasting feeling of vivacity.
Energy drinks are considered the most controversial source of caffeine. In addition to the stimulant itself, they often contain large amounts of sugar, flavors, and additional stimulants. Doctors associate regular consumption of energy drinks with increased stress on the cardiovascular system, especially in adolescents and people with anxiety disorders. Research shows that it is the combination of high doses of caffeine and sugar that can have a particularly strong effect on the nervous system, causing energy spikes and subsequent exhaustion.
What happens when you consume too much caffeine?
Despite its reputation as a relatively safe stimulant, caffeine can cause serious side effects if consumed excessively. The most common symptoms of overdose are anxiety, irritability, palpitations, tremors, insomnia, and concentration problems. People with increased anxiety and sleep disorders are especially sensitive to caffeine.
Psychologists note that caffeine can literally mimic the symptoms of an anxiety disorder. Expert Susan Bowling explains that stimulation of the nervous system causes physiological reactions similar to anxiety: rapid pulse, tension and inner anxiety.
Research also shows that the response to caffeine is strongly influenced by genetics. Some people process it quickly, while others process it much more slowly. Therefore, the same dose of coffee can have almost no effect on one person and cause insomnia in another.
A separate problem is the effect of caffeine on sleep. In 2025, researchers from the University of Montreal found that caffeine alters brain activity even during sleep. With the help of electroencephalography and artificial intelligence, scientists have found that under the influence of caffeine, the brain remains in a more agitated state and goes worse into deep recovery phases. One of the authors of the study, Professor Karim Djerbi, said that caffeine can "push the brain to a state of increased criticality," which is why the nervous system continues to remain overly active even at night.
Scientists from the University of Basel have also found that regular consumption of caffeine temporarily affects the structure of the gray matter of the brain. The researchers emphasize that the changes do not look irreversible, but they demonstrate how strongly the stimulant affects the nervous system.
Why are coffee and tea still considered healthy?
Paradoxically, despite all the risks, moderate consumption of coffee and tea is regularly associated with a positive effect on health. Large epidemiological studies show that people who consume coffee and tea in moderation often have a lower risk of cardiovascular disease, type II diabetes, and certain neurodegenerative diseases.
In 2026, researchers from Harvard and Mass General Brigham analyzed data from more than 130,000 people and concluded that two to three cups of coffee or one to two cups of tea a day could be associated with a reduced risk of dementia and improved cognitive function. Dr. Daniel Wang of the Harvard School of Public Health emphasized that caffeine cannot be considered a "cure for dementia," but moderate consumption of coffee and tea can be part of a healthy lifestyle along with physical activity and a good night's sleep.
The benefits of coffee and tea are explained not only by caffeine. These drinks contain antioxidants, polyphenols and other biologically active substances. Tea is especially rich in them, especially green tea. Some studies also show the potential benefits of coffee for the heart. Scientists from Germany have discovered that caffeine can improve the functioning of mitochondria, the energy centers of cells, and help protect the cardiovascular system.
Interestingly, the new data is gradually changing the understanding of the effect of caffeine on arrhythmia. Previously, doctors often recommended that people with heart rhythm disorders completely give up coffee. However, UCSF studies have shown that caffeine alone has not shown a consistent association with arrhythmia attacks.
How much coffee and tea can you drink without harm
Most current recommendations agree that a safe dose is considered to be about 400 mg of caffeine per day for a healthy adult. This is equivalent to about three to four cups of coffee. Such conclusions are confirmed by the recommendations of the US Food and Drug Administration (FDA), as well as research data on the effects of moderate caffeine consumption on the cardiovascular and nervous systems.
However, doctors emphasize that there is no universal norm. People with anxiety, hypertension, sleep disorders, pregnant women, and adolescents are often advised to significantly reduce their caffeine intake. Studies show that even moderate doses can have a stronger effect on people with hypersensitivity of the nervous system or slow metabolism of caffeine.
Experts advise not to consume caffeine late at night — studies by the University of Montreal have shown that caffeine can change brain activity even during sleep and impair the quality of body recovery, avoid regular consumption of energy drinks — especially in adolescents and people with cardiovascular diseases, since the combination of caffeine and sugar increases the load on the heart and nervous system, take into account hidden sources caffeine — soda, chocolate, sports supplements, and some painkillers, as well as gradually reducing the dose when anxiety, insomnia, or palpitations occur. Abrupt withdrawal from caffeine can cause headaches, irritability, and decreased concentration.
Experts also recommend paying attention not only to the amount of caffeine, but also to the shape of the drink. Black coffee and unsweetened tea are considered significantly safer than sugary energy drinks or coffee drinks with lots of syrups and sugar. Studies have linked caffeinated sweetened beverages with an increased risk of obesity and metabolic disorders.
Modern science shows that caffeine is neither an absolute evil nor a universal health remedy. Its effect on the body depends on the dosage, lifestyle and individual characteristics of a person. Moderate consumption of coffee and tea can actually be beneficial: maintain concentration, improve cognitive function, and even reduce the risk of certain diseases. But excess caffeine can disrupt sleep, increase anxiety, and overload the nervous system.
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