Drinking two or more daily cups of coffee is associated with roughly twice the risk of a premature death from cardiovascular disease in people with severe hypertension, a new study suggests.
One cup of coffee a day doesn’t appear to carry this risk, and neither does green tea, according to study results published in the Journal of the American Heart Association.
“These findings may support the assertion that people with severe high blood pressure should avoid drinking excessive coffee,” said senior study author Hiroyasu Iso, MD, PhD, MPH, in a statement. Dr. Iso serves as a director of the Institute for Global Health Policy Research at the National Center for Global Health and Medicine in Tokyo, said.
“To the best of our knowledge, this is the first study to find an association between drinking two or more cups of coffee daily and cardiovascular disease mortality among people with severe hypertension,” Iso noted.
Coffee May Protect Heart Health — but Perhaps Not for People With Severe Hypertension
Some previous research has linked a daily cup of coffee to a lower risk of so-called “cardiac events” and deaths from cardiovascular disease among heart attack survivors. Iso and his team had expected, then, to see that people with severe hypertension would benefit from drinking coffee.
This was not the case. “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,” Iso said.
What Is High Blood Pressure and Severe High Blood Pressure?
High blood pressure, also known as hypertension, occurs when the force of blood pushing against the walls of blood vessels is consistently too high, making the heart work harder to pump blood, per the American Heart Association.
Blood pressure is measured in millimeters of mercury (mmHg). Blood pressure readings are given as two values: The first is the pressure when the heart beats (systolic) and the second is the pressure when the heart relaxes (diastolic).
Current guidelines from the American Heart Association and the American College of Cardiology classify hypertension as a blood pressure reading of 130/80 mmHg or higher. In the United States, blood pressure of at least 140/90 is considered serious and blood pressure of at least 180/120 is considered a medical emergency, per Mayo Clinic.
For the new study, which followed more than 18,000 adults in Japan for roughly two decades, scientists defined severe hypertension as blood pressure of at least 160/100 mmHg.
Heavy Coffee Drinkers Had Other Cardiovascular Risk Factors
One limitation of the study is that people who consumed the most coffee were more likely to have several risk factors for developing and dying from cardiovascular disease, including smoking, drinking alcohol, and eating few vegetables.
Another research limitation is that the total number of cardiovascular disease deaths, and the subset of these fatalities in participants with severe hypertension, was too small to draw broad conclusions about the potential benefits or harms of coffee.
A third drawback is that researchers relied on study participants to accurately recall and report on how much coffee and tea they consumed.
The Sugar and Saturated Fat in Your Coffee Might Be an Issue
One further limitation of the study is that scientists lacked data on how people prepared these beverages — so they didn’t know if people loaded their drinks with sugar or cream or drank black coffee or plain green tea.
“Black coffee and mocha-frappa-crap-puccino might both qualify as coffee, but the latter is a sugar and saturated fat delivery vehicle,” says Christopher Gardner, PhD, a nutrition scientist and professor of medicine at Stanford University in California, who wasn’t involved in the study.
Likewise, “Green tea and boba or bubble tea are similar in terms of both possibly qualifying as tea, but the latter is more of a tea-flavored beverage with sugar and dairy and other additives,” Dr. Gardner adds.
The Bottom Line on Coffee and Severe Hypertension
“A simple takeaway is that if you do have severe hypertension and enjoy coffee, consider limiting your consumption to one cup a day,” Gardner says.
The study didn’t conclude that people should cut out coffee altogether, he adds, or suggest any benefits from switching to tea.