What you should know about new research on coffee and heart risks

Coffee lovers — and their doctors — have long wondered if a java jolt could affect the heart. New research published Wednesday shows that drinking caffeinated coffee doesn’t significantly affect a type of heart hiccup that can feel like a skipping beat.
But it signaled a slight increase in another type of irregular heartbeat in people who drank more than one cup a day. And it turns out that people tend to walk more and sleep less on the days they drink coffee.
Coffee is one of the most popular beverages in the world. According to the National Coffee Association, a trade group, two-thirds of Americans drink coffee every day, more than bottled water, tea, or tap water. Coffee contains caffeine, a stimulant that’s considered safe for healthy adults at about 400 milligrams per day, which equates to about four or five cups brewed at home.
Coffee has been linked to several health benefits and even a reduced risk of death, based on large studies that observed participants’ behavior. Despite research showing that moderate coffee consumption does not increase the risk of cardiac arrhythmias, some medical societies still warn against caffeine consumption.
The latest research:
The researchers outfitted 100 healthy volunteers with devices that continuously monitored their heart function, daily steps, sleep patterns and blood sugar. The volunteers, most of whom were under the age of 40, received text messages every day for two weeks instructing them to drink or avoid caffeinated coffee on certain days. The findings were published Wednesday in the New England Journal of Medicine.
This type of study that directly measures the biological effects of drinking or not drinking caffeinated coffee in the same people is rare and provides a dense array of data points, said study co-author Dr. Gregory Marcus, a cardiologist at the University of California, San Francisco, specializing in the treatment of cardiac arrhythmias.
The researchers found that drinking caffeinated coffee did not lead to more daily episodes of extra heartbeats, known as premature atrial contractions. These extra beats, which start in the upper chambers of the heart, are common and don’t usually cause problems. However, they have been shown to predict a potentially dangerous heart condition called atrial fibrillation.
They also found slight evidence of another type of irregular heartbeat coming from the lower chambers of the heart called premature ventricular contractions. Such beats are also common and usually not serious, but have been linked to a higher risk of heart failure. The researchers found more of these early hits in people on the days they drank coffee, but only in those who drank two or more cups a day.
The volunteers took about 1,000 more steps a day on the days they drank coffee — and they slept about 36 minutes less, according to the study. There was almost no difference in blood sugar levels.
An interesting finding: people with genetic variants that cause them to break down caffeine faster lost less sleep, while people with variants that cause them to metabolize caffeine more slowly lost more sleep.
Because the study was conducted on a small number of people over a short period of time, the results don’t necessarily apply to the general population, said Dr. Dave Kao, a cardiologist and health data expert at the University of Colorado School of Medicine, who was not involved with the study. However, the study agrees with others who have found coffee to be safe and offers a rare controlled assessment of caffeine’s effects, Kao added.
Co-author Marcus warns that the effects of drinking coffee can vary from person to person. He said he advises his patients with arrhythmias to experiment for themselves to see how caffeine affects them.
“They often rejoice in the good news that it’s okay to taste coffee and drink coffee,” he said.
The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.

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