In a new review paper, Dr. Gregory Marcus from the University of California, San Francisco and colleagues analyzed decades of research on how caffeine — most often consumed as coffee — affects the heart and its risk factors. They defined moderate intake as up to about 400 mg of caffeine a day, roughly three to five 8-ounce cups (a fluid ounce is 30 ml) of coffee.
Marcus et al. conclude that moderate caffeine or coffee consumption is safe for most adults and is linked to a lower risk of several cardiovascular conditions, including coronary heart disease, stroke, heart failure and atrial fibrillation, as well as hypertension and type 2 diabetes. Image credit: Sci.News.
With use dating as far back as 2737 BCE, caffeine is the world’s most popular stimulant and psychoactive substance.
Today, more than 60 different plant species, including cacao beans and tea leaves, naturally contain caffeine in varying degrees; however, caffeine can also be found in many over-the-counter, prescription, and other commercially available food products.
Caffeine is a methylxanthine derivative with alkaloid properties that can be administered orally, intravenously, topically, or rectally.
As a result of its 100% oral bioavailability and high hydrophilicity, caffeine rapidly undergoes dissolution and is absorbed on consumption, reaching peak concentrations in one hour.
Although caffeine does not accumulate in tissues or organs, high concentrations of caffeine (up to 80%) can be found in the brain.
Based on the results of the latest studies reviewed by Dr. Marcus and co-authors, consuming up to 400 mg of caffeine per day, or no more than 3 to 5, 8-ounce cups of regular black caffeinated coffee per day (without sugars, sweeteners, flavors or added fillers), is considered safe for most adults.
A regular brewed, non-specialty, caffeinated coffee typically contains 9.4-20.6 mg of caffeine per fluid ounce.
“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,” Dr. Marcus said.
“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.”
According to the paper, consuming caffeinated coffee without added sugars, flavors or cream was linked to a lower risk of Type 2 diabetes, heart disease, stroke, heart failure and some irregular heart rhythms.
Randomized trials, the most rigorous and reliable type of study design, have shown that caffeine consumption in coffee is associated with a lower risk of atrial fibrillation but also a higher risk of premature ventricular contractions.
Adding sugar, flavored syrups, milk and/or cream to coffee likely reduces its potential health benefits, and more research is needed to understand the impact of these additives.
Higher caffeine intake, such as levels found in energy drinks including energy shots, was associated with cardiovascular harm, such as increased risk of 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.
“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,” Dr. Marcus said.
“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.”
The review paper was published today in the journal Circulation.
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Gregory M. Marcus et al. Caffeine and Cardiovascular Disease: A Scientific Statement from the American Heart Association. Circulation, published online July 20, 2026; doi: 10.1161/CIR.0000000000001454
