In a comprehensive review, Dr. Gregory Marcus from the University of California, San Francisco, and his team delved into extensive research on how caffeine, primarily consumed through coffee, impacts cardiovascular health and its risk factors. They classify moderate caffeine consumption as up to 400 mg per day, equivalent to roughly 3 to 5 cups (8 ounces each) of coffee.

Caffeine consumption dates back to 2737 BC and remains the most widely used stimulant and psychoactive agent across the globe.

Over 60 plant species, such as cocoa beans and tea leaves, naturally produce caffeine. Additionally, caffeine is present in many commercial and prescription products, as well as various over-the-counter foods.

Caffeine is classified as a methylxanthine and has alkaloid characteristics that can be administered orally, intravenously, topically, or rectally.

Thanks to its complete oral bioavailability and high solubility, caffeine is quickly dissolved and absorbed after ingestion, achieving maximum concentration within one hour.

While caffeine does not accumulate in organs or tissues, it can reach significant concentrations (up to 80%) in the brain.

Based on Dr. Marcus’s recent research, a daily intake of up to 400 mg of caffeine, or 3 to 5 cups of regular, black caffeinated coffee (without sugar or additives), is considered safe for most adults.

Standard brewed coffee typically contains between 9.4 to 20.6 mg of caffeine per fluid ounce.

“Caffeine intake from coffee plays a crucial role in the daily routines of millions. Our review confirms that for the majority of adults, consuming up to 400 mg per day—or up to five cups of black coffee without added sugars or fillers—is safe and does not increase cardiovascular risk,” said Dr. Marcus.

“Conversely, high doses of caffeine found in energy drinks and energy shots can pose risks to heart health and should be avoided.”

The findings indicate that consuming black coffee without added sugars, flavors, or cream is linked to a lower risk of type 2 diabetes, heart disease, stroke, heart failure, and certain irregular heartbeat patterns.

Rigorous randomized trials show an association between caffeine consumption from coffee and a decreased risk of atrial fibrillation, though they also indicate a potential increase in premature ventricular beats.

Incorporating sugar, flavored syrups, milk, or cream into coffee may lessen its health benefits, necessitating further exploration into the effects of these additives.

Excessive caffeine intake, especially from energy drinks, is linked to cardiovascular issues, including heightened blood pressure and irregular heart rhythms.

Energy shots can possess 40 to 69 mg of caffeine per fluid ounce, considerably exceeding the caffeine levels in standard brewed coffee.

“While evidence suggests caffeine may offer cardiovascular benefits for some, individual responses can vary widely, influenced by age, medications, existing health conditions, genetics, and metabolic rates,” stated Dr. Marcus.

“A caffeine dose safe for one individual may lead to adverse effects like heart palpitations, anxiety, or sleep disturbances in another.”

It’s essential to observe personal reactions to caffeine and consult healthcare professionals regarding appropriate consumption levels.

For further reading, refer to the review paper published in today’s 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 on July 20, 2026. doi: 10.1161/CIR.0000000000001454