A morning coffee is part of daily life for millions of people, and many studies have linked moderate coffee drinking with possible health benefits.
But research suggests that drinking two or more cups a day may be risky for people whose blood pressure is very high.
The study found that people with blood pressure of 160/100 mm Hg or higher who drank at least two cups of coffee each day had about twice the risk of dying from cardiovascular disease compared with people in the same blood pressure group who did not drink coffee.
High blood pressure, also called hypertension, forces the heart and blood vessels to work harder. Over time, it can damage arteries and organs and greatly increase the risk of heart attack, stroke and other serious cardiovascular problems.
Coffee has a more complicated relationship with heart health. It contains caffeine, which can temporarily increase blood pressure and make the heart beat faster in some people, but it also contains many plant compounds that may have beneficial effects.
Previous research has linked moderate coffee consumption with lower risks of several chronic diseases. Some studies have also suggested that coffee may be associated with better survival among people who have previously had a heart attack.
The new findings suggest that the effects of coffee may depend partly on a person’s existing health. For someone with severely elevated blood pressure, the stimulating effects of a larger amount of caffeine could potentially become more important.
Researchers examined information from more than 18,000 adults in Japan, including over 6,570 men and more than 12,000 women. Participants were between 40 and 79 years old and provided information about their coffee and green tea drinking habits.
The researchers divided participants into different groups based on their blood pressure. They then followed them over time to examine deaths from cardiovascular disease, which includes conditions affecting the heart and blood vessels.
Among people with severe hypertension, drinking two or more cups of coffee each day was associated with roughly double the risk of cardiovascular death. However, drinking one cup a day was not linked to an increased risk, even among people with high blood pressure.
Green tea showed a different pattern. Regular green tea consumption was not associated with a higher risk of cardiovascular death in any of the blood pressure groups studied, even though green tea also contains caffeine.
One possible explanation is that green tea contains large amounts of polyphenols. These natural plant compounds have antioxidant and anti-inflammatory properties, although the study cannot prove that they are responsible for the difference between coffee and tea.
The results also do not prove that drinking coffee directly caused the additional deaths. The study was observational, meaning researchers looked for patterns in people’s habits and health rather than randomly assigning people to drink different amounts of coffee.
People with severely high blood pressure should therefore not assume that they must completely give up coffee based on this study alone. However, those who regularly drink several cups a day may want to discuss their caffeine intake with a doctor, especially if their blood pressure remains poorly controlled.
Managing hypertension remains one of the most important ways to protect the heart. Taking prescribed medicine, reducing excess salt, exercising regularly, maintaining a healthy diet, avoiding smoking and monitoring blood pressure can all help reduce cardiovascular risk.
The research was led by Hiroyasu Iso and was published in the Journal of the American Heart Association. The findings suggest that when it comes to coffee, a person’s blood pressure may matter just as much as the number of cups they drink.
If you care about high blood pressure, please read studies about breakfast for better blood pressure management, and the gut feeling that lowers blood pressure.
For more health information, please see recent studies about how the dash diet helps lower blood pressure, and how to eat your way to healthy blood pressure.
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