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Love coffee? You’re hardly alone. But what is the caffeine in your mug doing to your heart health?

An ·¬ÇÑÊÓƵ scientific statement, recently published in , has summed up the latest findings. Here are highlights.

Is coffee bad for you?

For most adults, drinking up to 400 milligrams of caffeine a day without added sugars or fillers is safe and does not increase cardiovascular risk, Dr. Gregory M. Marcus, a professor of medicine at the University of California, San Francisco School of Medicine, said in a .

That much caffeine is the equivalent of three to five 8-ounce cups of caffeinated coffee.

“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,” said Marcus, who is also the associate chief of cardiology for research at the University of California, San Francisco Health.

Marcus led the writing group that wrote the statement, which details the most recent research primarily on caffeinated coffee and the potential effects of its caffeine on , cholesterol, coronary heart disease, high blood pressure, Type 2 diabetes, heart rhythm issues and other cardiovascular conditions.

The statement’s authors noted that research on caffeine’s effects on the cardiovascular system is challenging and that many areas require more study.

Why is caffeine research complicated?

Most studies on caffeine are observational, meaning they cannot prove cause and effect. Also, while coffee is the main source of caffeine in most studies, the observed effects may be due to other compounds.

For example, some research suggests that other bioactive compounds in coffee may have antioxidant and anti-inflammatory properties, which may help explain some health benefits. Even so, it’s difficult to separate the effects of caffeine from other ingredients added to coffee, such as milk, cream, flavored syrups and sugar.

Latest findings about coffee, caffeine and heart health

Consuming caffeinated coffee without added ingredients was linked to a lower risk of Type 2 diabetes, heart disease, stroke, heart failure and some irregular heart rhythms.

Sugar, milk or cream probably reduce coffee’s potential health benefits, and the authors said more research was needed on the effects of these additives.

The statement also addressed:

• Blood pressure: Caffeinated coffee may affect blood pressure differently depending on how much is consumed. In people with healthy blood pressure levels, drinking one to three cups a day was associated with an increased risk of developing high blood pressure, while drinking more than three cups a day was associated with a lower risk.

  High doses of caffeine, such as those from energy drinks, can significantly increase blood pressure, especially in people who already have high blood pressure.

• Type 2 diabetes: Caffeinated coffee may reduce insulin sensitivity in the short term. Drinking caffeinated coffee with no flavors or sweeteners regularly also was linked to a lower risk of developing Type 2 diabetes. This may be due to compounds in coffee other than caffeine.

• Cholesterol: Randomized clinical trials – the most rigorous and reliable type of study – indicate that cafestol, a component 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. It’s not found in coffee brewed with paper filters or instant coffee.

• Heart disease and stroke: Drinking two to four cups of caffeinated coffee a day was linked to a lower risk of heart disease, heart failure and stroke. However, drinking more than four cups of caffeinated coffee a day may increase the risk of heart failure (where the heart can’t pump enough blood).

• Heart rhythm: Analyses that use self-reported information from participants have found that drinking from one to three cups of caffeinated coffee a day was not associated with an increased risk of atrial fibrillation or abnormal heart rhythm.

However, caffeinated coffee at that same level may be associated with premature ventricular contractions – early beats from the lower chamber of the heart.

Very high doses of caffeine, such as those in caffeinated energy drinks or energy shots, have been linked to abnormal heart rhythm in people usually considered to have low cardiovascular disease risk, such as healthy adults younger than age 30.

How much caffeine is in a cup of coffee, anyway?

A regular brewed, non-specialty coffee typically contains from 9.4 to 20.6 mg of caffeine per fluid ounce.

Energy drink shots may contain three to four times more caffeine than regular coffee.

What about caffeine in tea and energy drinks?

While fewer studies have focused on tea than coffee, tea has been associated with reduced risk of atrial fibrillation, heart failure and stroke, similar to caffeinated coffee.

Energy drinks, bars, gels and caffeine-based supplements often contain other added ingredients that may increase the absorption of caffeine, may accelerate its effects on the body, may raise blood pressure and increase the risk of cardiovascular harm.

How caffeine affects the body and heart health

Caffeine consumed through coffee is metabolized by the liver and generally reaches peak concentration for most people within an hour. How quickly individuals process caffeine depends on their genetics, metabolism, age and past caffeine use.

Short-term effects of caffeine may include temporary increases in blood pressure, heart rate, blood sugar and alertness. Heart palpitations and/or sleep disruption also are possible.

Some people may develop a tolerance to higher levels of caffeine.

Does caffeine affect everyone the same way?

“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,” Marcus said.

What may be a reasonable amount for one person could cause unwanted effects, such as heart palpitations, anxiety or sleep disruption, in another, he said. “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.”

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