A cup of coffee in the morning is part of many people's daily routines. But for some, that extra pick-me-up turns into multiple pours per day.
New research suggests that's a bad habit if for people with high blood pressure. A study by the Journal of the American Heart Association found that people with hypertension who drink two or more cups of coffee per day can double their risk of dying from heart attacks, strokes and other cardiovascular diseases.
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This finding provides a slight counter to previous research, which suggests coffee can protect drinkers against numerous conditions.
"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," senior study author Dr. Hiroyasu Iso said in a news release.
While that protective appears to have limits, the study found that drinking one cup of coffee per day or any amount of green tea did not increase the risks of fatal heart disease, regardless of the participant's hypertension levels.
The study, conducted in Japan, comprised 6,574 men and 12,035 women from 30 Japanese communities. All of the people included in the research were 40-79, and were already part of a separate study on cancer risks. Researchers enrolled participants between 1988-1990, tracking their diets, lifestyles and medical histories until 2009. Subjects self-reported their coffee and tea consumption throughout the study, while blood pressure was measured once and not updated throughout the process.
According to the American Heart Association, high blood pressure is a reading of 130 mmHg or higher over 80 mmHg or higher. For the research study, blood pressure levels were put into five categories: normal (less than 130/85), high normal (130-139/85-89), grade 1 hypertension (140-159/90-99), grade 2 (160-179/100-109) and grade 3 (180/110 or higher).
Coffee consumption was associated with an increased risk of death from heart disease among those in the grade 2 and 3 categories.
Previous studies have suggested that coffee drinkers live longer and that the beverage protects against Parkinson's disease, type 2 diabetes, liver disease, heart attacks and stroke. Research published in the Annals of Internal Medicine also found that people who drink any amount of unsweetened coffee were 16% to 21% less likely to die prematurely than those who do not drink coffee.
Harvard's School of Public Health concluded that drinking coffee does not increase the risk of health issues such as cardiovascular diseases and cancers. On the contrary, drinking three to five cups of coffee daily was associated with a lower risk of many chronic diseases.
The European Journal of Endocrinology also studied the health benefits of coffee on both type 2 diabetes and cardiovascular disease. While the researchers acknowledged "considerable evidence of long-term health benefits" for moderate coffee drinkers — those who consume 3-4 cups per day — they cautioned that coffee's effects on heart and liver disease, as well as glucose, are still not fully understood.