Coffee is one of the most widely consumed psychoactive substances on the planet, yet despite more than two billion cups being drunk each day, its impact on heart health remains surprisingly complex – and often misunderstood.
It's been blamed for heart palpitations, anxiety and poor sleep, while at the same time praised for helping to deliver focus, better moods and lower chronic disease risk. In 2025, a handful of new studies helped us cut through the noise when it comes to the heart, chronic disease and mortality. Randomized trials, imaging tools and biochemical analysis also helped us get a clearer understanding of coffee's power.
One study challenged long-held assumptions about caffeine and irregular heart rhythms, while another showed how something as simple as a paper filter can change cholesterol impact and lower cardiovascular risk. And a third found a correlation between protection from chronic disease and when in the day you imbibed.
At a time of the year when we might be upping our caffeine intake to deal with the holidays, we thought it would be fitting to revisit these three excellent studies on coffee.
World-first findings on coffee and irregular heartbeat
University of Adelaide and University of California, San Francisco (UCSF) researchers led a randomized clinical trial of 200 adults from Australia, the US and Canada with atrial fibrillation (AF) to test coffee's impact on irregular heartbeats. Over six months, 100 of the participants consumed at least one cup of coffee or an espresso shot each day, while the other half abstained from all types of caffeine.
At the end of the trial, those who continued caffeinated coffee experienced a 47% recurrence rate of AF or atrial flutter, compared with 64% in the caffeine-abstinent group, translating to about a 39% lower risk of recurrence for coffee drinkers. There were no significant differences in adverse effects between the groups. This is the first randomized clinical evidence suggesting moderate coffee consumption may protect against the return of AF – a result that counters decades of conventional advice to avoid caffeine for people with irregular heart rhythms.
"The results were astounding," said first author Professor Christopher X. Wong from the University of Adelaide and Royal Adelaide Hospital. "In contrast to conventional wisdom, we found the coffee drinkers experienced a significant reduction in AF compared to those who avoided coffee and caffeine.
"This is surprising as it goes against the common assumption by doctors and patients that coffee worsens heart rhythm disorders such as AF. Doctors have always recommended patients with problematic AF minimize their coffee intake, but this trial suggests that coffee is not only safe but likely to be protective."
The research was published in The Journal of the American Medical Association.
Coffee brewing, diterpenes, cholesterol and heart health
Uppsala University researchers looked into how coffee's brewing methods could affect levels of natural compounds called diterpenes that can raise low-density lipoprotein (also known as LDL or "bad" cholesterol) levels and impact cardiovascular health. What they found was quite remarkable.
"Considering how much coffee is consumed in Swedish workplaces, we wanted to get a picture of the content of cholesterol-elevating substances in coffee from these types of machines," said corresponding author David Iggman, a researcher at the university’s Clinical Nutrition and Metabolism Unit. "We studied 14 coffee machines and could see that the levels of these substances are much higher in coffee from these machines than from regular drip-filter coffee makers."
Of the 14 pieces of equipment, 11 were brewing coffee machines and three were liquid-model machines. Samples were also taken of homemade coffee brews for comparison, which included drip-brewed, percolator, French press/cafetière, and boiled methods. Each sample was then analyzed with liquid chromatography-tandem mass spectrometry (LC-MS), and cafestol and kahweol levels were measured.
Among the fascinating findings, the researchers discovered that coffee from brewing machines had higher diterpene concentrations than paper-filtered coffee, but lower than boiled coffee. For liquid-model machines, there was one outlier sample with unusually high concentrations of cafestol and kahweol – but when this was omitted, the brewing method was on par with paper-filtered variants.
"From this, we infer that the filtering process is crucial for the presence of these cholesterol-elevating substances in coffee," Iggman said. "Obviously, not all coffee machines manage to filter them out. But the problem varies between different types of coffee machines, and the concentrations also showed large variations over time."
The researchers also estimated that replacing three cups of brewing-machine coffee with paper-filtered coffee five days a week would reduce LDL cholesterol by 0.58 mmol/L.
"For people who drink a lot of coffee every day, it’s clear that drip-filter coffee, or other well-filtered coffee, is preferable," Iggman said.
The study was published in the journal Nutrition, Metabolism & Cardiovascular Diseases.
Timing your coffee right can lower chronic disease risk
Tulane University researchers looked at data from more than 40,000 adults who tracked their daily nutritional intake, including how much coffee they drank and when they drank it, and saw a pattern emerge.
"Research so far suggests that drinking coffee doesn't raise the risk of cardiovascular disease, and it seems to lower the risk of some chronic diseases, such as type 2 diabetes," said Ju Qi from Tulane University. "Given the effects that caffeine has on our bodies, we wanted to see if the time of day when you drink coffee has any impact on heart health."
Participants were split into groups based on the timing of their coffee consumption. About 36% consumed their coffee in the morning, while another 16% had their intake spread throughout the whole day. And 48% of the people studied were not coffee drinkers.
After adjusting for variables, the researchers found that, compared to people who didn't drink coffee at all, morning drinkers were 16% less likely to die from all-cause mortality and had a 31% lower rate of death from cardiovascular disease than non-drinkers or those who drank t ithroughout the day.
"This is the first study testing coffee drinking timing patterns and health outcomes," said Qi. "Our findings indicate that it's not just whether you drink coffee or how much you drink, but the time of day when you drink coffee that's important. We don't typically give advice about timing in our dietary guidance, but perhaps we should be thinking about this in the future."
The study was published in the European Heart Journal.
