According to research published in the Journal of the American Heart Association, drinking two or more cups of coffee a day may double the risk of death from cardiovascular disease in people with severe high blood pressure (160/100 mm Hg or higher), but not in people with high blood pressure not considered severe. 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.
The study’s senior author, Hiroyasu Iso, explained that the 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. The study is the first to find an association between drinking two or more cups of coffee daily and cardiovascular disease mortality among people with severe hypertension.
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. 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; and 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.
However, too much coffee may raise blood pressure and lead to anxiety, heart palpitations, and difficulty sleeping. The FDA notes that an 8-ounce cup of green or black tea has 30-50 milligrams of caffeine, while an 8-ounce cup of coffee has closer to 80 to 100 milligrams.