Drinking two or more cups of coffee a day may double the risk of death from cardiovascular disease among people with severe high blood pressure (160/100 mm Hg or higher) but not people with high blood pressure not considered severe, according to research published today in the Journal of the American Heart Association, an open access, peer-reviewed journal of the American Heart Association.
In contrast, the study found that one cup of coffee and daily green tea consumption did not increase the risk of death related to cardiovascular disease at any blood pressure measurement, though both drinks contain caffeine. According to the FDA, an 8-ounce cup of green or black tea has 30-50 milligrams of caffeine, and an 8-ounce cup of coffee has closer to 80 to 100 milligrams.
Previous research found that drinking one cup of coffee a day may help heart attack survivors by lowering their risk of death after a heart attack and may prevent heart attacks or strokes in healthy individuals. In addition, separate studies have suggested drinking coffee regularly may reduce the risk of developing chronic illnesses, such as Type 2 diabetes and some cancers; may help to control appetite; may help to lower the risk of depression or boost alertness, though it is not clear if this effect is from the caffeine or something else in coffee. On the harmful side, too much coffee may raise blood pressure and lead to anxiety, heart palpitations and difficulty sleeping.
“Our study aimed to determine whether the known protective effect of coffee also applies to individuals with different degrees of hypertension; and also examined the effects of green tea in the same population,” explained the study’s senior author Hiroyasu Iso, M.D., Ph.D., M.P.H., director of the Institute for Global Health Policy Research, Bureau of International Health Cooperation, National Center for Global Health and Medicine in Tokyo, Japan, and professor emeritus at Osaka University. “To the best of our knowledge, this is the first study to find an association between drinking 2 or more cups of coffee daily and cardiovascular disease mortality among people with severe hypertension.”
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. It is measured in millimeters of mercury (mm Hg). The current blood pressure guidelines from the American Heart Association and the American College of Cardiology classifies hypertension as a blood pressure reading of 130/80 mm Hg or higher.
The blood pressure criteria for this study are slightly different from the ACC/AHA guidelines. Researchers classified blood pressure into five categories: optimal and normal (less than 130/85 mm Hg); high normal (130-139/85-89 mm Hg); grade 1 hypertension (140-159/90-99 mm Hg); grade 2 (160-179/100-109 mm Hg); and grade 3 (higher than 180/110 mm Hg). Blood pressure measures in grades 2 and 3 were considered severe hypertension in this study.
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