Just two cups a day can increase the risk of CVD death for people with severe hypertension, researchers have found.
Two or more cups of coffee a day doubles the risk of dying from cardiovascular disease in people with severe hypertension, a Japanese study has found.
The analysis of 18,000 people aged 40-79 years found that those with systolic blood pressure over 160–179mmHg or diastolic blood pressure over 100–109mmHg had an elevated risk of dying when they drank two or more cups of coffee a day.
There was no elevated risk detected for those with normal blood pressure or less severe hypertension, the researchers found.
“The present study may support the assertion that heavy coffee consumption should be avoided among people with severe hypertension,” they wrote in the Journal of the American Heart Association.
Study participants self-reported their daily coffee drinking habits, and their blood pressure was measured after a five-minute rest at the testing location.
Most participants drank instant or drip-brewed coffee, the researchers reported in the prospective observational study.
During the 19-year study follow-up, there were 842 cardiovascular disease deaths, the researchers reported.
“Among people with grade two to three hypertension, coffee consumption of at least two cups/day was associated with an increased risk of cardiovascular disease mortality, compared with non-drinkers,” they wrote.
“Further adjustment for potential confounding factors did not materially change the association.
“No significant association between coffee consumption and cardiovascular disease mortality was found among people with optimal and normal blood pressure, high-normal blood pressure, or grade one hypertension.”
The researchers defined grade two hypertension as systolic blood pressure of 160–179mmHg or diastolic blood pressure of 100–109mmHg, and grade three hypertension as systolic blood pressure of at least 180mmHg or diastolic blood pressure of at least 110mmHg.
They also found that people who drank coffee more frequently were more likely to be younger, be current smokers and drinkers, eat fewer vegetables and have higher total cholesterol levels and lower systolic blood pressure regardless of their blood pressure category.
The researchers said previous research had shown that coffee consumption could reduce the risk of incident hypertension and mortality in the general population. This study, however, investigated the effect of coffee and green tea consumption across different blood pressure categories.
“Little is known about whether the protective effect of coffee consumption exists for people with severe hypertension,” they said.
The researchers said chlorogenic acid and other phenolic compounds, magnesium and trigonelline in caffeinated coffee had been shown to lower serum cholesterol levels, improve endothelial function, and reduce inflammation in women with diabetes.
“Habitual coffee drinkers can also develop caffeine tolerance, which may reduce the adverse effects of caffeine on cardiovascular disease outcomes.”
The researchers said the harmful effects of caffeine such as transient blood pressure elevation would be offset by the beneficial effects of the compounds found in coffee and tolerance to caffeine in the general population.
“However, because people with hypertension are more susceptible to the effects of caffeine, caffeine’s harmful effects may outweigh its protective effects and increase the risk of mortality in people with severe hypertension.”
As for green tea, the study found that drinking green tea was not associated with an increased risk of cardiovascular disease across any blood pressure categories.
The researchers said the mechanism underlying the beneficial effects of green tea may be explained by the effect of epigallocatechin 3-gallate, the most abundant polyphenol in green tea.
“We recently reported that 7 or more cups of green tea consumed per day was associated with a reduced risk of all-cause mortality among people with a history of stroke or myocardial infarction by 62% and 53%, respectively, compared with non-drinkers.”
Journal of the American Heart Association 2023, online 17 January
