Does Coffee or Green Tea Consumption Impact Cardiovascular Disease Mortality in Hypertension?

Heavy coffee consumption may increase the risk for mortality due to cardiovascular disease (CVD) in people with severe hypertension, whereas green tea does not increase CVD mortality risk regardless of hypertensive status. These are the findings of a study published in the Journal of the American Heart Association. 

Researchers in Japan conducted a nationwide, community-based, prospective study obtaining data from the Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC) in which 18,609 participants (12,035 women, 6574 men) between the ages of 40 and 79 were initially enrolled between 1988 and 1990 and followed up until 2009.

Researchers divided participants into 4 groups according to hypertension categories: optimal or normal blood pressure (BP) (<130 mmHg), high-normal BP (130-139 mmHg), grade 1 hypertension (140-159 mmHg), and grades 2-3 hypertension (160 mmHg and above).

Participants completed questionnaires about the frequency and amount of coffee and green tea consumption with the following options: almost every day, 3 to 4 cups per week, 1 to 2 cups per week, 1 to 2 cups per month, and almost never. Those who responded almost every day were questioned about the number of cups per day.

Researchers accounted for confounding variables, including height, weight, body mass index (BMI), total cholesterol levels, lifestyle factors such as alcohol consumption, smoking status, and exercise and eating habits, medication use, history of diabetes, and mental health status.

They assessed participant mortality by identifying death certificates through the Ministry of Health and Welfare and ascertained the cause of death using ICD-10 codes.

Researchers further evaluated participants who died due to CVD regarding their coffee and green tea drinking habits. They did this to determine if consumption of either beverage increased the risk for mortality due to CVD and whether hypertension had an impact.

During the 18.9 year follow-up period, 842 deaths occurred due to CVD. Coffee consumption of more than 2 cups per day increased risk for CVD mortality in participants with grades 2 or 3 hypertension compared with those who did not drink coffee (hazard ratio [HR], 2.05; 95% CI, 1.17-3.59, P =.09). The researchers did not observe any correlation between coffee consumption and CVD mortality risk in participants with normal BP, high-normal BP, or grade 1 hypertension. Adjusting for confounders did not substantially change these results.

In contrast, green tea consumption did not correlate with increased risk for CVD mortality in individuals with grades 1-3 hypertension. Interestingly, people with normal BP who consumed 1-2 cups of green tea per day and people with high-normal BP who consumed 5 to 6 cups of green tea per day actually demonstrated a borderline reduced risk for CVD mortality, but following adjustment for confounders, the association no longer remained significant.

Researchers noted that drinking 2 cups or more of coffee, was tied to a higher risk for CVD mortality among people with severe hypertension, but not those without hypertension or with grade 1 hypertension. Any consumption of green tea was not related to CVD mortality risk across all hypertension categories.

They concluded, “The present study may support the assertion that heavy coffee consumption should be avoided among people with severe hypertension.”

Study limitations included self-reported consumption of coffee and green tea allowing the potential for false reporting, use of only baseline consumption and BP measures without accounting for possible changes in consumption habits or BP over the nearly 20-year follow-up. Other limitations included potential coding errors for cause of death, potential residual confounding factors, and the observational design of the study, which precludes the assumption of causation.