For people with very high blood pressure, drinking several cups of coffee each day may carry an unexpected heart risk.
A large study found that people with severe hypertension who drank two or more cups of coffee daily had about twice the risk of dying from heart and blood vessel disease as those who did not drink coffee. The same increased risk was not seen with one daily cup or with green tea.
High blood pressure, also called hypertension, forces the heart and blood vessels to work harder than normal. Over time, it can damage arteries and increase the risk of heart attack, stroke and other serious conditions. A reading of 160/100 mm Hg or higher is considered very high and requires medical attention.
The researchers studied 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 when they entered the research. Their blood pressure, coffee and green tea consumption, lifestyle and health were recorded and then followed over many years.
The clearest difference appeared among people with the highest blood pressure. Those who drank at least two cups of coffee a day had roughly double the risk of death from cardiovascular disease compared with people in the same blood pressure group who did not drink coffee. Drinking only one cup a day was not linked to the same increase.
This does not mean coffee is unhealthy for everyone. Previous research has linked moderate coffee drinking with several possible health benefits, including a lower risk of some chronic diseases. Coffee contains many biologically active substances, so its effects are more complicated than simply the amount of caffeine it provides.
However, caffeine can temporarily raise blood pressure and may increase heart rate in some people. It can also cause palpitations, anxiety or sleep problems, particularly in people who are sensitive to it. For someone whose blood pressure is already dangerously high, these effects may be more important.
Green tea produced a different result. The researchers did not find an increased risk of cardiovascular death with green tea consumption, even among participants with severe hypertension. This was notable because green tea also contains caffeine.
One possible explanation involves plant compounds called polyphenols, which are abundant in green tea. These substances have antioxidant and anti-inflammatory effects and may influence the heart and blood vessels in beneficial ways. However, the study did not prove that polyphenols were responsible for the difference between coffee and tea.
The research also cannot prove that drinking two cups of coffee directly caused the additional deaths. It was an observational study, meaning researchers followed people’s habits rather than assigning them to drink specific amounts of coffee. Other differences between frequent coffee drinkers and non-drinkers could have influenced the results.
For people with severe hypertension, the findings suggest that coffee intake is worth discussing with a healthcare professional. They should not rely on changing coffee habits alone to manage their condition. Blood pressure treatment may include prescribed medicine, regular monitoring, physical activity, a healthy diet, reducing excess salt and avoiding smoking.
People with normal or moderately elevated blood pressure should not assume from this study that they need to stop drinking coffee. The increased cardiovascular risk was specifically observed among people with severe hypertension who consumed two or more cups each day. Individual responses to caffeine can also vary considerably.
The study was published in the Journal of the American Heart Association. The findings suggest that the health effects of coffee may depend partly on a person’s existing cardiovascular health and reinforce a simple point: what is safe or beneficial for most people may not have the same effect in someone with severely high blood pressure.
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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