Coffee is the most popular beverage in the United States, according to the National Coffee Association—outpacing water, soft drinks, juice and tea. In fact, Americans consume roughly 517 million cups of coffee each day.

Too much coffee, however, could be bad news for people with severe hypertension, according to a new study showing heavy coffee drinkers who also have high blood pressure may be more likely to die from CVD-related death (JAHA. 2022;0:e026477).

For the study, published in the Journal of the American Heart Association, researchers tapped data from the Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC) comprising nearly 20,000 participants who completed self-administered questionnaires about their lifestyles, diets and medical history, and who underwent health examinations. Participants were enrolled between 1988 and 1990, and were followed up until 2009 for a median of 18.9 years. At baseline, participants were 40 to 79 years old.

Participants were asked to answer questions about the frequency of coffee consumption and grouped according to four categories: occasionally or none, less than one cup per day, one cup per day, and two or more cups per day.

As part of the health examinations, each participant’s blood pressure was measured during the study. Participants were grouped into one of five categories, according to blood pressure: optimal and normal, high‐normal, grade 1 hypertension, grade 2 hypertension and grade 3 hypertension.

During the follow-up period of the study, a total of 842 cardiovascular deaths occurred among participants.

Results showed heavy coffee consumption—two or more cups per day—was associated with an increased risk of CVD mortality among people with severe hypertension, but not in people without hypertension or with grade 1 hypertension.

The researchers also evaluated the impact of habitual green tea consumption on CVD-related death in people with or without hypertension. They found no association between CVD mortality and green tea intake, regardless of hypertension status.

In fact, they found green tea drinkers with high-normal or optimal blood pressure may experience a heart health boost. A “borderline reduced risk” of CVD mortality was seen among these groups of habitual green tea drinkers, researchers reported.

The researchers suggested the caffeine in coffee may be to blame for its potential negative effects in people with hypertension.

“…Because people with hypertension are more susceptible to the effects of caffeine, caffeine’s harmful effects may outweigh its protective effects and increase the risk of mortality in people with severe hypertension,” they wrote.

While green tea, too, contains caffeine, it also contains high amounts of health-boosting polyphenols, which have been shown to reduce blood pressure levels and inflammation, among other benefits.

“These beneficial effects of green tea catechins may partially explain why only coffee consumption was associated with an increased risk of mortality in people with severe hypertension despite both green tea and coffee containing caffeine,” researchers wrote.