But the study, published in the New England Journal of Medicine, has found some downsides to an everyday cuppa. It showed that people lost about 36 minutes of sleep each night on days they drank coffee — and the more coffee they drank, the less sleep they got.
The research also looked at the effect of coffee on heart palpitations, a fairly common experience for healthy coffee drinkers. The study found that in healthy men and women, coffee did not cause a common type of palpitation known as premature atrial contraction, even though some health authorities have warned that this may be a side effect of drinking coffee.
But coffee consumption can lead to an increase in another type of heart palpitation, known as premature ventricular contractions. These extra or irregular heartbeats are quite common and pleasant. Almost everyone experiences them from time to time, and while they can be scary, most experts say they’re usually not a cause for concern in healthy people.
The findings suggest that the health effects of coffee are complex. Although coffee is beneficial for many people and can lower the risk of chronic diseases and perhaps even extend your life, it can also disrupt your sleep and may cause some heart palpitations.
“The truth is that coffee is not all good or all bad – it has different effects,” said Gregory M. Marcus, an author of the study and a professor of medicine in the division of cardiology. at the University of California at San Francisco. “Overall, this study indicates that coffee consumption is almost certainly safe. But people should recognize that there are real and measurable physiological effects that can — depending on the individual and their goals of care — is harmful or helpful.”
Classification of the effects of coffee on general health
Coffee is among the most common beverages in the world, and decades of research suggest that it often has beneficial effects. Many observational studies show that coffee drinkers live longer and have lower rates of diabetes, cancer, liver disease, depression and other chronic conditions. But most of the data comes from large epidemiological studies, which show only correlations, not cause and effect. They also rely on self-reported data, which is not always reliable.
At the same time, research on coffee and cardiovascular health is somewhat contradictory. Early learning indicated that coffee can be harmful to the heart because it increases blood pressure, heart rate and adrenaline, and increases cholesterol levels.
More recent studies have found that drinking a few cups of coffee every day – including decaffeinated coffee – can actually lower the risk of dying from heart disease or stroke, which some experts have linked to to the large amount of antioxidants and other anti-inflammatory compounds in coffee.
Despite the lack of strong evidence, health authorities often warn people with heart conditions, especially those with heart rhythm disorders such as atrial fibrillation, to avoid coffee and other beverages. with caffeine because of concern that they may trigger palpitations.
To better understand the effects of coffee on health, Marcus and his colleagues recruited 100 healthy men and women in San Francisco and fitted them with Fitbits, continuous glucose monitors and electrocardiogram devices that track to their heart rhythms around the clock for 14 days.
Each participant followed a strict coffee schedule: They were instructed to drink as much caffeinated coffee as they wanted for two days, then abstain for two days, and repeat this cycle for two week. Participants were told to press a button on their heart monitors every time they drank a cup of coffee to document their intake in real time.
To make sure the participants followed the instructions, the researchers sent them daily reminders and even paid them if they provided date-stamped coffee receipts. They also used a form of virtual surveillance called geofencing to monitor coffee-shop visits.
New data on coffee, sleep and exercise
On the days they drank coffee, participants tended to consume about one to three cups, although some drank less, and some drank up to six cups of coffee daily.
Coffee has a clear effect on sleep. People got about 7.2 hours of nightly shut-eye on days they avoided coffee and 6.6 hours on days they drank it.
Genetics seem to play a role: People who carry genetic variants that make them so-called “slow metabolizers” of caffeine had a greater reduction in their sleep when they drank coffee compared to ” rapid metabolizers,” possibly because caffeine stays in their systems longer. (Many direct-to-consumer DNA testing companies such as 23andMe will tell you whether your genes make you a fast or slow metabolizer of caffeine.)
The effects on physical activity are particularly noticeable. Marcus at UCSF said it’s unclear why people walked an extra 1,000 steps on days they drank coffee. They may have had more energy and motivation.
Either way, taking an extra 1,000 steps per day was associated with a 6 to 15 percent reduction in mortality — “effect sizes remarkably similar to the size of the mortality benefit observed in coffee drinkers, ” says the study.
“That’s a clinically relevant difference in physical activity that may have long-term positive implications,” Marcus said.
Researchers are particularly interested in how coffee affects the heart. Premature atrial contractions are a type of irregular heartbeat that originate in the upper chambers of the heart, called the atria, while premature ventricular contractions originate in the lower chambers, called the ventricles. . Almost everyone experiences these palpitations on a normal basis, which can feel like your heart fluttered or skipped a beat.
The researchers found that on days when people drank more than one cup of coffee, they experienced about 50 percent earlier ventricular contractions. Although these are not considered dangerous, there is some evidence that this may be a warning to people who experience a lot of them.
An observational study in 2015 Marcus was a co-author of the finding that people who regularly experienced many of these palpitations were more likely to develop heart failure. “It doesn’t mean everyone,” said Marcus. “But we know that the more you have, the higher the risk.”
Amit Khera, a cardiologist who was not involved in the study, called it unique and important. He said most people should not worry about the potential for coffee to cause palpitations because in healthy adults there is no indication that they are dangerous. But he cautioned that the findings don’t necessarily apply to people with heart disease.
“In healthy people with normal hearts, this is what I would call a quality-of-life issue, not a life-threatening issue,” said Khera, the director of the preventive cardiology program at the University of Texas Southwestern Medical Center. “If you feel like your heart is skipping a beat and it’s bothering you, then based on the results of this study cutting out coffee may reduce those symptoms.”
Peter Kistler, an expert in heart rhythm disorders who studies the health effects of coffee, said that even people experienced earlier ventricular contractions on days they drank coffee, the incidence is low and the palpitations are “totally benign.” “People should be reassured that coffee is safe and part of a healthy diet,” said Kistler, the head of clinical electrophysiology research at the Baker Heart and Diabetes Institute in Melbourne.
Marcus said the finding warrants further investigation. But in the meantime, people should tailor their coffee intake to their individual needs. If you need motivation to exercise then consider using coffee to give you a boost. But if you suffer from insomnia or you’re worried that you’re at high risk for heart failure because it runs in your family, then consider cutting back, Marcus says.
“There is no one size fits all prescription or recommendation,” he added. “It really depends on the individual.”
Do you have a question about healthy eating? Email EatingLab@washpost.com and we may answer your question in a future column.
