Drinking Two or More Cups of Coffee Daily May Double Risk of Heart Death in People With Severe Hypertension

 

 
 

Drinking two or more cups of coffee a day may double the risk of death from cardiovascular disease (CVD) 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 in the 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 CVD at any blood pressure measurement, though both drinks contain caffeine. According to the FDA (U.S. Food and Drug Administration), an 8-oz. cup of green or black tea has 30-50 mg of caffeine, and an 8-oz. cup of coffee has closer to 80-100 mg.

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.

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.

Study participants included more than 6,570 men and more than 12,000 women, ages 40 to 79 years at the start of the research. They were selected from the Japan Collaborative Cohort Study for Evaluation of Cancer Risk—a large, prospective study established between 1988 and 1990 of adults living in 45 Japanese communities. Participants provided data through health examinations and self-administered questionnaires assessing lifestyle, diet and medical history.

During nearly 19 years of follow-up (through 2009), 842 cardiovascular-related deaths were documented. The analysis of data for all participants found:

• Drinking two or more cups of coffee a day was associated with twice the risk of CVD death in people whose blood pressure was 160/100 mm Hg or higher compared to those who did not drink any coffee.
• Drinking one cup of coffee a day was not associated with increased risk of death from cardiovascular disease across any blood pressure categories.
• Green tea consumption was not associated with an increased risk of CVD mortality across any blood pressure categories.

The study found that people with more frequent coffee consumption were more likely to be younger, current smokers, current drinkers, eat fewer vegetables, and have higher total cholesterol levels and lower systolic blood pressure (top number) regardless of the blood pressure category.

The benefits of green tea may be explained by the presence of polyphenols, which are micronutrients with healthy antioxidant and anti-inflammatory properties found in plants. The researchers noted that polyphenols may be part of the reason only coffee consumption was associated with an increased risk of death in people with severe high blood pressure despite both green tea and coffee containing caffeine.

The research has several limitations: coffee and tea consumption were self-reported; blood pressure was measured at a single point, which did not account for changes over time; and the observational nature of the study could not draw a direct cause-and-effect connection between coffee consumption and cardiovascular disease risk among people with severe high blood pressure.

Further study is needed, researchers said, to learn more about the effects of coffee and green tea consumption in people with high blood pressure and to confirm the effects of coffee and green tea consumption in other countries.

For more information, visit www.heart.org.