For many people, the day doesn’t really begin until they can get their first cup of coffee in their hands. Besides giving you the kick you need in the morning to get in gear, research has also found that java can have significant health benefits in some cases. But as a powerful stimulant, there are still plenty of reasons to watch how much joe you’re putting back. And now, a new study has found that drinking just two cups of coffee a day can double the risk of death from heart disease for those with high blood pressure. Read on to see if you should be holding off on ordering that next cup.
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The latest insight on coffee’s potential health effects comes from a study published in the Journal of the American Heart Association (JAHA) on Dec. 21. To gather data, a team of researchers used 6,574 men and 12,035 women taking part in the Japan Collaborative Cohort Study for Evaluation of Cancer Risk. All participants in the group were between the ages of 40 and 79 when they signed up for the study between 1988 and 1990.
Participants were followed through 2009, during which time they self-reported their coffee and tea consumption habits and had their lifestyle, diet, and medical history assessed by using data collected during health exams and questionnaires, according to a statement from the American Heart Association (AHA). Blood pressure was taken at a single point during the study, allowing the team to classify each participant into one of five groups based on their readings. The categories were split up as optimal and normal at a blood pressure of 130/85; high normal at 130-139/85-89; grade 1 hypertension from 140-159/90-99; grade 2 hypertension at 160-179/100-109; and grade 3 hypertension for readings 180/110 or higher. For the purposes of the study, anyone with a reading of 160/100 or higher was considered to have severe hypertension.
Results of the team’s analysis found that study participants in the severe hypertension category that drank two or more cups of coffee per day saw their risk of death from heart disease double when compared to those who didn’t drink any coffee.
But while the findings point to coffee consumption as a potential health issue, it wasn’t a problem across the board. Drinking just one cup a day did not raise the risk of cardiovascular disease-related deaths. And no amount of green tea—which is also a caffeinated beverage—was shown to affect any group.
“We were surprised that heavy coffee consumption was associated with an increased risk of cardiovascular disease mortality among people with severe hypertension, but not in those without hypertension or with grade 1 hypertension,” Masayuki Teramoto, MD, the study’s author from Osaka University Graduate School of Medicine in Japan and the department of epidemiology and biostatistics at the University of California, San Francisco, told HealthDay. “In contrast, green tea consumption was not associated with an increased risk of cardiovascular disease mortality across all blood pressure categories.”
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In its press release announcing the new research, the AHA points out that previous studies have actually found there to be some health benefits to coffee. One 2021 study published in the journal Circulation: Heart Failure found that an increase in coffee consumption was matched with a decrease in the risk of heart failure. The organization also cited other research that found coffee consumption could actually reduce the risk of hypertension in patients who haven’t already been diagnosed with the condition.
Researchers in the latest study also pointed out that the elevated risk may not be related to caffeine at all given the findings with green tea. Instead, they explained that the antioxidant and anti-inflammatory properties of polyphenols found in the beverage could be behind the correlation.
“These beneficial effects of green tea may partially explain why only coffee consumption was associated with an increased risk of mortality in persons with severe hypertension, despite both green tea and coffee containing caffeine,” Teramoto told HealthDay.
Ultimately, the researchers said that the study had some limitations, including that data for coffee and tea consumption were self-reported and that no further blood pressure readings were taken to account for changes over time. The team also said further research was necessary to establish a more solid link between coffee or green tea consumption and blood pressure using more diverse participant groups. But they did conclude that their findings did point to some potential lifestyle decisions for those with hypertension.
“These findings may support the assertion that people with severe high blood pressure should avoid drinking excessive coffee,” Hiroyasu Iso, MD, PhD, the study’s senior author and director of the Institute for Global Health Policy Research at the National Center for Global Health and Medicine in Tokyo, said in a press release. “Because people with severe hypertension are more susceptible to the effects of caffeine, caffeine’s harmful effects may outweigh its protective effects and may increase the risk of death.”