Caffeine

For most adults, a daily caffeine habit may be safer for the heart than many people assume. A new American Heart Association review found that up to 400 milligrams of caffeine a day, roughly three to five cups of regular black coffee, is generally safe and may even be linked to lower risks of heart disease, stroke, heart failure, and Type 2 diabetes. But the source matters: highly concentrated energy drinks and shots can sharply raise blood pressure and trigger irregular heart rhythms.Caffeine is the most widely used stimulant and psychoactive substance in the world, and coffee is how 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/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 at higher doses. Concentrated sources of caffeine, especially energy drinks including energy shots, may raise the risk of cardiovascular problems. The findings were published in the American Heart Association's flagship peer-reviewed journal Circulation in the scientific statement "Caffeine and Cardiovascular Disease." "Caffeine consumed in coffee is a key part of daily life for millions of people, and in our review of the most recent research, for most adults, intake of up to 400 mg of caffeine/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 Chair of the scientific statement volunteer writing group Gregory M. Marcus, M.D., M.A.S., FAHA, a professor of medicine at the University of California, San Francisco School of Medicine and the 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, may have harmful effects on the heart and should be avoided." Why Caffeine Research Is Complicated Understanding exactly how caffeine affects the cardiovascular system is difficult. 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 possible benefits. It is also hard to distinguish the effects of caffeine from those of ingredients commonly added to coffee, including milk, cream, flavored syrups and/or sugar. Most caffeine research is observational as well, which means it can identify associations but cannot establish cause and effect. Coffee is not the only source of caffeine. Tea, chocolate, soda and energy drinks, as well as over-the-counter and prescription medications, can all add to 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 about 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? Based on 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 equal to no more than 3 to 5, 8-ounce cups of regular black caffeinated coffee per day (without sugars, sweeteners, flavors or added fillers). Regular brewed, non-specialty, caffeinated coffee usually contains 9.4-20.6 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, which are considered the most rigorous and reliable study design, have linked caffeine from coffee to a lower risk of atrial fibrillation. However, the same research also connected it with a higher risk of premature ventricular contractions. Adding sugar, flavored syrups, milk and/or cream may weaken coffee's potential health benefits. Researchers say more work is needed to determine exactly how these additions affect health outcomes. High caffeine intake 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 may contain 40-69 mg of caffeine per fluid ounce, 3-4 times more caffeine than regular caffeinated coffee. What Caffeine Does Inside the Body After caffeine from coffee enters the body, it is processed by the liver and usually reaches its highest concentration within about an hour. The speed at which this happens varies according to genetics, metabolism, age, and previous caffeine use. People who regularly consume larger amounts of caffeinated coffee may gradually develop a tolerance. Others can experience strong effects from much smaller amounts. In the short term, caffeine may temporarily increase blood pressure, heart rate, blood sugar and alertness. It can also cause heart palpitations and/or sleep disruption in some people. Caffeine and Blood Pressure Coffee may affect blood pressure differently depending on how much a person drinks. Among people with optimal blood pressure, consuming 1-3 cups a day was associated with a greater risk of developing high blood pressure. Surprisingly, drinking more than 3 cups per day was associated with a lower risk. High doses of caffeine (such as those from energy drinks or energy shots) can cause significant increases in blood pressure. This effect may be especially concerning 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 black, caffeinated coffee (no additives, flavors, or sweeteners) was associated with a lower risk of developing Type 2 diabetes. Scientists do not yet know whether 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 vs. various compounds in coffee. Coffee Preparation May Affect Cholesterol Randomized clinical trials have found that cafestol, a substance present in both caffeinated and decaffeinated coffee, was associated with higher levels of low-density lipoprotein (also known as "bad" cholesterol). Cafestol is found in unfiltered coffee (such as espresso, French press, Turkish coffee or boiled coffee) but is not found in coffee prepared with paper filters or in instant coffee. Researchers still need to determine which products contain the highest levels of cafestol and how it affects cholesterol. Coffee, Caffeine and Heart Rhythm Recent analyses based on participant-reported health information found that consuming 1-3 cups of caffeinated coffee per day was not associated with a higher risk of atrial fibrillation or abnormal heart rhythm. However, that same amount may be linked to more premature ventricular contractions (or PVCs). These are early beats that begin in the lower chamber of the heart. Very high caffeine doses (such as those in caffeinated energy drinks or energy shots) have been associated with abnormal heart rhythms even in people who are normally considered at low risk for cardiovascular disease, including healthy adults younger than age 30. Heart Disease, Heart Failure and Stroke Drinking 2-4 cups of caffeinated coffee per day was associated with lower risks of heart disease, heart failure and stroke. However, the relationship may change at higher levels. Consuming more than 4 cups of caffeinated coffee a day may increase the risk of heart failure. Not All Caffeine Sources Are Equal Researchers emphasize that caffeine products should not all be treated as interchangeable. More studies are needed to compare different kinds of caffeinated coffee with tea, soda, energy drinks and energy shots, and foods. Tea has received less research attention than coffee. Even so, tea consumption has been associated with reduced risks of atrial fibrillation, heart failure and stroke, similar to caffeinated coffee. Energy drinks, bars, gels and caffeine-based supplements may contain additional ingredients that help the body absorb caffeine more rapidly. These additives may speed up caffeine's effects, increase blood pressure and raise the risk of cardiovascular harm. 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 caffeine source affects cardiovascular health. The researchers also highlighted the limited evidence available for caffeinated energy drinks and other increasingly popular caffeine products. Because there is not yet enough rigorous evidence to establish formal intake recommendations, caffeine was not included in the Association's 2026 Dietary Guidance to Improve Cardiovascular Health. "Although research suggests that caffeine consumption may be associated with certain cardiovascular benefits for some people, it's important to remember that there is no 'one-size-fits-all' strategy for safe caffeine consumption. People can respond very differently to caffeine based on various 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 disruption, in another. That's why it's important to pay attention to how your body responds to caffeine and talk with your healthcare team about what is right for you," Marcus said. Key Findings Co-authors are Vice Chair Frank B. Hu, M.D., M.P.H., Ph.D., FAHA; Rob M. van Dam, Ph.D.; Marilyn C. Cornelis, Ph.D.; Thomas A. Dewland, M.D.; JungHee Kang, Ph.D., M.P.H., R.N.; Susanna C. Larsson, Ph.D.; Robert L. Page II, Pharm.D., M.S.P.H., FAHA; and Niyati Parekh, Ph.D., FAHA. Authors' disclosures are listed in the manuscript.