People with high blood pressure who drink just two coffees a day could be doubling their risk of a heart death, a new study reveals. Researchers studied 18,600 men and women aged between 40 and 79 following them up for another 19 years.
They found that two cups of coffee a day was enough to double the risk of death from those with severe hypertension defined as 160/100 mm Hg or higher. However, it was not all bad news, with those having one cup of coffee or drinking green tea, both of which contain caffeine, showing no adverse effects.
Previous research has 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.
It may also help to control appetite, 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.
Senior study author Professor Hiroyasu Iso at Osaka University said: "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. To the best of our knowledge, this is the first study to find an association between drinking two or more cups of coffee daily and cardiovascular disease mortality among people with severe hypertension.”
High blood pressure 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. During nearly 19 years of follow-up, 842 cardiovascular-related deaths were documented.
Analysis of the data found drinking two or more cups of coffee a day was associated with twice the risk of cardiovascular disease 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 cardiovascular disease mortality across any blood pressure categories. Prof Iso, director of the Institute for Global Health Policy Research, Bureau of International Health Cooperation, National Center for Global Health and Medicine in Tokyo, Japan added: ”These findings may support the assertion that people with severe high blood pressure should avoid drinking excessive coffee.
“Because people with severe hypertension are more susceptible to the effects of caffeine, caffeine’s harmful effects may outweigh its protective effects and may increase the risk of death.”
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.
In the study published in the Journal of the American Heart Association Japanese participants provided data through health examinations and self-administered questionnaires assessing lifestyle, diet and medical history.
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 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 researchers noted their study 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.
