New research published in the Journal of the American Heart Association has shown that drinking two or more cups of coffee per days can double the risk of death resulting from cardiovascular disease among people with severe hypertension—that is, 160/100 mm Hg and above. These findings do not apply to those with mild hypertension and those without hypertension.

 Previous research has established that coffee can benefit health, such as by lowering risk of developing cardiovascular disease and arrhythmias. Coffee and green tea are also thought to lower risk of death for heart attack and stroke survivors.

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But in the words of Renaissance German scientist Paracelsus, “The dose makes the poison.” Too much coffee now appears to be linked to higher rates of death by cardiovascular disease in people with severe hypertension. The new study consisted of more than 18,000 participants from Japan, of which roughly 60 percent were female and the other 30 percent were male, ranging in age from 40 to 79 years at the start of the study. Over 19 years, the participants provided information on their health, lifestyle, diet, and medical history. After analyzing the data, the researchers had three key findings:

• Drinking two or more cups of coffee per day was associated with twice the risk of death from cardiovascular disease in those with severe hypertension
• Drinking only one cup of coffee per day had no associations with increased risk across any participants, regardless of blood pressure
• No amount of green tea consumption was associated with higher risk of death from cardiovascular disease

“These findings may support the assertion that people with severe high blood pressure should avoid drinking excessive coffee,” said study author Hiroyasu Iso. “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 risk of death.” The researchers say that further study is needed to learn more about the effects of coffee and green tea consumption on those with hypertension and to confirm that the effects are the same in other countries.