Coffee is one of the most popular beverages in the world, and the United States is no exception. According to the National Coffee Association, two-thirds of Americans drink coffee every day, which is more than bottled water, tea, or tap water. While coffee contains caffeine, a stimulant that is widely regarded as safe for healthy adults at about 400 milligrams per day, some professional medical societies still caution against consuming caffeine.
Despite this caution, research has shown that moderate coffee consumption may have health benefits, including a lower risk of dying. Large studies that observed participants’ behavior found that moderate coffee consumption did not raise the risk of heart rhythm problems. However, there is a need for more direct measures of the biological effects of drinking or not drinking caffeinated coffee.
A recent study published in the New England Journal of Medicine aimed to provide a more direct measure of the effects of caffeinated coffee on heart function. The study outfitted 100 healthy volunteers with gadgets that continuously monitored their heart function, daily steps, sleep patterns, and blood sugar. The volunteers, who were mostly younger than 40, were sent daily text messages over two weeks instructing them to drink or avoid caffeinated coffee on certain days.
The study found that drinking caffeinated coffee did not result in more daily episodes of extra heartbeats, known as premature atrial contractions. These extra beats that begin in the heart’s upper chambers are common and typically don’t cause problems. But they have been shown to predict a potentially dangerous heart condition called atrial fibrillation.
The researchers did find slight evidence of another kind of irregular heartbeat that comes from the lower heart chambers, called premature ventricular contractions. Such beats are also common and not usually serious, but they have been associated with a higher risk of heart failure. The researchers found more of these early beats in people on the days they drank coffee, but only in those who drank two or more cups per day.
The volunteers logged about 1,000 more steps per day on the days they drank coffee — and they slept about 36 minutes less, the study found. There was almost no difference in blood sugar levels. People with genetic variants that make them break down caffeine faster experienced less of a sleep deficit, while folks with variants that lead them to metabolize caffeine more slowly lost more sleep.
Although the study was performed on a small number of people over a short period of time, the results are consistent with others that have found coffee to be safe. Co-author Dr. Gregory Marcus, a cardiologist at the University of California, San Francisco, who specializes in treating heart arrhythmias, cautions that the effects of drinking coffee can vary from person to person. He advises his patients with heart arrhythmias to experiment on their own to see how caffeine affects them.
In conclusion, this study offers a rare controlled evaluation of caffeine’s effect on heart function, and the results suggest that moderate coffee consumption is safe for healthy adults. However, as with any dietary choice, it is always important to consider individual factors and consult with a healthcare professional.