Caffeine is the most widely used stimulant and psychoactive substance in the world, and coffee is the way most people consume it. According to a new scientific statement from the American Heart Association, most adults can safely consume up to 400 mg of caffeine per day (or up to five 8-ounce cups of caffeinated coffee per day). For some people, moderate coffee consumption may also be associated with a lower risk of cardiovascular disease.
The picture changes with higher doses. Concentrated sources of caffeine, especially energy drinks, including energy shots, may increase the risk of cardiovascular problems. The findings were published in the American Heart Association’s leading peer-reviewed journal. Circulation in the scientific statement “Caffeine and cardiovascular diseases.”
“Caffeine consumed in coffee is a key part of daily life for millions of people, and in our review of the latest research, for most adults, intake of up to 400 mg of caffeine per day, the equivalent of up to 5 cups of caffeinated coffee per day without added sugars or fillers, is safe and does not increase cardiovascular risk,” said voluntary scientific statement writing group chair Gregory M. Marcus, MD, MAS, FAHA, professor of medicine at the University of California, San Francisco. Francisco School of Medicine and associate chief of Cardiology for Research at the University of California, San Francisco Health. “However, high doses of caffeine, such as those found in energy drinks, including energy shots, can have harmful effects on the heart and should be avoided.”
Why caffeine research is complicated
It is difficult to understand exactly how caffeine affects the cardiovascular system. Coffee is the main source of caffeine in most studies, but coffee contains many other substances that could influence health. Experimental research suggests that some bioactive compounds in coffee have antioxidant and anti-inflammatory properties, which may contribute to its potential benefits.
It is also difficult to distinguish the effects of caffeine from those of ingredients commonly added to coffee, such as milk, cream, flavored syrups, and/or sugar. Most research on caffeine is also observational, meaning it can identify associations but cannot establish cause and effect.
Coffee is not the only source of caffeine. Tea, chocolate, soft drinks, and energy drinks, as well as prescription and over-the-counter medications, can increase a person’s daily intake. Researchers say more studies are needed to clarify the caffeine content and cardiovascular effects of these other products.
The new statement reviews recent evidence on caffeinated coffee and its possible relationships with high blood pressure, cholesterol, type 2 diabetes, coronary heart disease, stroke, heart failure, atrial fibrillation, other arrhythmias, and other cardiovascular conditions.
How much caffeine is considered safe?
According to the latest studies included in the review, up to 400 mg of caffeine per day is considered safe for most adults. That amount is roughly equivalent to no more than 3 to 5 8-ounce cups of regular caffeinated black coffee per day (no added sugars, sweeteners, flavors or fillers). Regularly brewed, non-specialty caffeinated coffee generally contains between 9.4 and 20.6 mg of caffeine per fluid ounce.
Drinking caffeinated coffee without added sugars, flavors or cream was associated with lower risks of type 2 diabetes, heart disease, stroke, heart failure and some irregular heart rhythms.
Randomized trials, considered the most rigorous and reliable study design, have linked caffeine in coffee to a lower risk of atrial fibrillation. However, the same research also linked it to an increased risk of premature ventricular contractions.
Adding sugar, flavored syrups, milk and/or cream can weaken the potential health benefits of coffee. Researchers say more work is needed to determine exactly how these additions affect health outcomes.
High caffeine consumption may pose greater risks. Levels commonly found in energy drinks, including energy shots, were associated with high blood pressure and irregular heart rhythm. Energy drink shots can contain between 40 and 69 mg of caffeine per fluid ounce, 3 to 4 times more caffeine than regular caffeinated coffee.
What does caffeine do inside the body?
Once the caffeine from coffee enters the body, it is processed by the liver and generally reaches its highest concentration in about an hour. The rate at which this happens varies depending on genetics, metabolism, age, and previous caffeine consumption.
People who regularly consume large amounts of caffeinated coffee may gradually develop a tolerance. Others may experience strong effects with much smaller amounts. In the short term, caffeine can temporarily increase blood pressure, heart rate, blood sugar, and alertness. It may also cause heart palpitations and/or sleep disturbances in some people.
Caffeine and blood pressure
Coffee can affect blood pressure differently depending on how much a person drinks. Among people with optimal blood pressure, consuming 1 to 3 cups a day was associated with an increased risk of developing high blood pressure. Surprisingly, drinking more than 3 cups a day was associated with a lower risk.
High doses of caffeine (such as those in energy drinks or energy shots) can cause significant increases in blood pressure. This effect can be especially worrying for people who already have high blood pressure.
Possible effects on type 2 diabetes
Research indicates that caffeinated coffee may temporarily reduce insulin sensitivity. At the same time, regularly drinking caffeinated black coffee (without additives, flavors or sweeteners) was associated with a lower risk of developing type 2 diabetes.
Scientists still don’t know if caffeine is responsible for that association. Other compounds in coffee may provide some or all of the benefit. Additional research is needed to separate the effects of caffeinated coffee from the various compounds in coffee.
Coffee preparation can affect cholesterol
Randomized clinical trials have found that cafestol, a substance present in both caffeinated and decaffeinated coffee, is associated with higher levels of low-density lipoproteins (also known as “bad” cholesterol).
Cafestol is found in unfiltered coffee (such as espresso, French press, Turkish coffee, or boiled coffee), but it is not found in coffee made with paper filters or instant coffee. Researchers still need to determine which products contain the highest levels of cafestol and how it affects cholesterol.
Coffee, caffeine and heart rate
Recent analyzes based on health information provided by participants found that consuming 1 to 3 cups of caffeinated coffee per day was not associated with an increased risk of atrial fibrillation or abnormal heart rhythm.
However, that same amount may be related to more premature ventricular contractions (or PVCs). These are the first beats that begin in the lower chamber of the heart.
Very high doses of caffeine (such as those in caffeinated energy drinks or energy shots) have been associated with abnormal heart rhythms even in people normally considered at low risk for cardiovascular disease, including healthy adults under 30 years of age.
Heart disease, heart failure and stroke
Drinking 2 to 4 cups of caffeinated coffee a day was associated with lower risks of heart disease, heart failure, and stroke.
However, the relationship can change at higher levels. Consuming more than 4 cups of caffeinated coffee a day may increase the risk of heart failure.
Not all sources of caffeine are the same
The researchers emphasize that not all caffeinated products should be considered interchangeable. More studies are needed to compare different types of caffeinated coffee with tea, soft drinks, energy drinks, energy shots, and foods.
Tea has received less scientific attention than coffee. Still, tea consumption has been associated with reduced risks of atrial fibrillation, heart failure, and stroke, similar to caffeinated coffee.
Caffeine-based energy drinks, bars, gels, and supplements may contain additional ingredients that help the body absorb caffeine more quickly. These additives can accelerate the effects of caffeine, increase blood pressure and increase the risk of cardiovascular damage.
More rigorous studies are needed
The writing group called for more randomized controlled trials examining caffeine in coffee and other caffeinated products. Scientists need a clearer understanding of why people respond differently and how each source of caffeine affects cardiovascular health.
The researchers also highlighted the limited evidence available on caffeinated energy drinks and other increasingly popular caffeinated products. Because there is not yet enough rigorous evidence to establish formal intake recommendations, caffeine was not included in the Association’s 2026 Dietary Guideline to Improve Cardiovascular Health.
“Although research suggests that caffeine consumption may be associated with certain cardiovascular benefits for some people, it is important to remember that there is no single strategy for safe caffeine consumption. People can respond very differently to caffeine depending on a variety of factors, such as age, medications, underlying health conditions, genetics, and how quickly their bodies metabolize it. What may be a reasonable amount for one person could cause unwanted effects, such as heart palpitations, anxiety, or sleep disturbances, in another. That’s why “It’s important to pay attention to how your body responds to caffeine and talk to your healthcare team about what’s right for you,” Marcus said.
Key findings
- The most recent evidence indicates that consuming up to 400 mg of caffeine per day (equivalent to up to five 8-ounce cups of caffeinated coffee per day) is generally safe for most adults. For some people, this level of intake may also be associated with lower risks of heart failure, heart disease, and stroke.
- Higher caffeine consumption, including the amounts found in energy drinks and energy shots, may increase the likelihood of high blood pressure and/or irregular heartbeat or arrhythmia.
- Researchers say more evidence is needed to determine how caffeine affects the body, how different sources of caffeine influence heart health and why the effects can vary so much from person to person.
Co-authors are Vice President Frank B. Hu, MD, MPH, Ph.D., FAHA; Rob M. van Dam, Ph.D.; Marilyn C. Cornelis, Ph.D.; Dr. Thomas A. Dewland; JungHee Kang, Ph.D., MPH, RN; Susanna C. Larsson, Ph.D.; Robert L. Page II, Pharm.D., MSPH, FAHA; and Niyati Parekh, Ph.D., FAHA. Author disclosures are listed in the manuscript.