AHA identifies safe caffeine threshold, flags above-limit cardiovascular risks

The American Heart Association (AHA) has published a scientific statement reviewing caffeine’s safety profile in existing research. It linked consuming up to 400 mg of caffeine per day to potentially lowering the risk of multiple cardiovascular conditions, including stroke, heart failure, and heart disease. 

However, exceeding that caffeine threshold may result in irregular heart rhythm and increased blood pressure. Energy drinks are examples of such drinks that contain high caffeine levels and may therefore bring negative health effects on cardiovascular health, warns the organization.

“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 per day, the equivalent of up to five cups of caffeinated coffee per day without added sugars or fillers, is safe and does not increase cardiovascular risk,” says first author of the study and chair of the scientific statement volunteer writing group, Gregory Marcus, M.D., M.A.S., and fellow of the AHA.

“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.”

Marcus is also a professor of medicine at the University of California (UC), San Francisco School of Medicine, and the associate chief of Cardiology for Research at the UC San Francisco Health.

Above threshold, opposite effects

The review found that the latest research indicates that 400 mg of caffeine daily is safe for most adults.

Research also showed that consuming caffeinated coffee without adding milk, sugar, flavors, or creams was linked to a lower risk of type 2 diabetes, heart disease, stroke, heart failure, and irregular heart rhythms. When added, these ingredients reduce the health benefits obtained. 

This creates a challenge in distinguishing whether health benefits come from caffeine or other compounds, or from other added ingredients, caution the authors.

AHA says that when caffeine is consumed through coffee, it is metabolized by the liver and usually reaches its peak concentration within an hour.They add that more research is needed to understand how this relationship works. 

AHA’s statement also details that randomized trials have demonstrated that caffeinated coffee is associated with a lower risk of atrial fibrillation — the most common type of irregular heartbeat — but an increased risk of premature ventricular contractions.

However, when consuming caffeine at levels above 400 mg daily, it is associated with opposite effects, including cardiovascular harm, high blood pressure, and irregular heart rhythm. Energy drinks and shots typically contain three to four times more caffeine than coffee, stresses the AHA.

The association explains that when caffeine is consumed through coffee, it is metabolized by the liver and usually reaches its “peak concentration” within an hour. This is dependent on genetics, metabolism, age, and caffeine tolerance, which may build up over time of consumption.

There are also short-term effects from caffeine, including increased blood pressure, heart rate, blood sugar, and alertness. It may also disrupt sleep or cause heart palpitations. 

Data also showed that cafestol, a component in both caffeinated and decaffeinated coffee, was associated with higher levels of low-density lipoprotein cholesterol (known as bad cholesterol). Cafestol is found in espresso, French Press, Turkish coffee, or boiled coffee, but not in paper-filtered or instant coffee. The authors note that more research is needed to determine the cause of this. 

Multiple sources of caffeine

Published in Circulation, the statement underscores that caffeine is one of the most consumed drugs globally. However, it notes that most current scientific evidence is based on observational studies of coffee rather than clinical trials of caffeine. 

Therefore, the observed health effects may be due to other compounds in coffee rather than caffeine, and due to the studies being observational, they cannot determine cause and effect.

There are multiple food sources that contribute to overall caffeine intake.The paper highlights that experimental studies have demonstrated that coffee has antioxidant and anti-inflammatory properties, which may be the reason for some observed health benefits. 

Previous studies have shown that coffee, both caffeinated and decaffeinated, can affect the gut microbiome, which in turn may influence mood and stress levels. It has also shown potential to improve cognitive performance and reduce inflammation in people with heart rhythm disorders or atrial fibrillation.

There are multiple food sources that also contribute to overall caffeine intake, including dark chocolate, tea, soda, energy drinks, and some over-the-counter and prescription medications. Therefore, the researchers stress the need for more research on caffeine and other products containing it, apart from 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,” says Marcus.

“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.”