For many people, coffee is one of life’s greatest pleasures—not to mention an energy boost. Recent studies have linked coffee to longer life and decreased risk of cardiovascular disease, among other potential health benefits. Yet for decades, conflicting research has suggested that coffee may lead to cardiovascular issues, particularly a type of dangerous irregular heartbeat called atrial fibrillation.
Now a new study led by researchers at the University of California San Francisco provides strong evidence that coffee is likely safe for people worried about developing atrial fibrillation. At the same time, it found that more than one cup a day can increase risk of premature ventricular contractions, which are a risk indicator for heart failure. It also provided several other findings about a cup of joe and your health.
An innovative study design
The authors dubbed their research the Coffee and Real-time Atrial and Ventricular Ectopy (CRAVE) trial. A team of researchers followed 100 adults, with an average age of 39, residing in San Francisco. Subjects wore Fitbits to track their step count, sleep duration and location (to monitor coffee shop visits). They also wore a continuous glucose monitor to measure blood sugar. Participants were randomly instructed via daily text messages to either drink caffeinated coffee or abstain from caffeine for two-day periods, over a total trial period of 14 days. They were not instructed how much coffee to drink.
Most coffee studies are observational, or epidemiological, meaning they observe health outcomes in people who already drink coffee and compare them to people who don’t. Observational studies are subject to many confounding factors—it’s hard to tell if health results are linked to coffee or something else.
The new study is a randomized case-crossover trial—participants were randomly assigned to either drink or not drink coffee for specified periods. The data on their coffee days was compared to data on their non-coffee days. This aspect of the study allowed it to more strongly establish a causal relationship between coffee consumption and the observed outcomes.
Good heart news
The study, “Acute Effects of Coffee Consumption on Health Among Ambulatory Adults,” was published in the New England Journal of Medicine on March 23. There were several interesting findings:
•The researchers found that coffee does not cause an increased number of premature atrial contractions in people without existing arrhythmia. These early beats, which happen in the upper part of the heart, are fairly common, though they are also an important predictor of atrial fibrillation. Dr. Gregory Marcus, lead author and associate chief of cardiology for research at UCSF Medical Center, says that “those concerned about their atrial fibrillation risk probably need not worry about their coffee consumption.”
• The team did find a possible link between consumption of more than one cup of coffee and increased premature ventricular contractions, which occur in the lower part of the heart and may raise risk of heart failure. Caffeine leads to the release of calcium in heart muscle cells, which in some cases causes premature ventricular contractions. Marcus notes that people “experiencing bothersome symptoms from premature ventricular contractions or those at especially high risk of heart failure may consider cutting down on or eliminating their coffee.”
• They also found that when people drank coffee, they took around 1,000 more steps a day. They note that an increase in 1,000 steps per day “has been associated with a 6 percent to 15 percent reduction in mortality, effect sizes that are remarkably similar to the magnitude of mortality benefit observed among coffee drinkers [in past studies].” While Marcus says “it may make sense to strategize the timing of one’s coffee consumption to potentially help motivate physical activity when desired,” he cautions against extrapolating the results “to other substances that are completely different, such as energy drinks.”
• Coffee drinkers also slept around half an hour less. The impact of the lost sleep, the researchers say, is unclear: “Although an hour less sleep per night correlates with substantially worse [health] outcomes, the effects of losing 30 minutes of sleep, as observed in our trial, are less certain.” Marcus adds that “people struggling with insomnia should consider a strict trial off coffee for a few days to see if it helps them. But clearly there is no one size fits all here.”
The study tested participants for genetic variations in how they process caffeine, which could account for differences in how coffee affects people’s health. People with genetic variants linked with faster caffeine metabolism had more premature ventricular contractions when they drank coffee, while people who seemed to process caffeine slower had greater reductions in sleep.
“I can’t say there is a universal prescription to recommend,” said Marcus. “Instead, it really depends on a given individual’s concerns, propensities and health goals.” As with incorporating wine into a healthy lifestyle, it’s best to consult your doctor and consider your own health before picking up, or putting down, a daily cup of joe.
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