Coffee is part of the daily routine for millions of people, and many studies have linked moderate coffee drinking with possible health benefits.
But research suggests that people with very high blood pressure may need to be more careful about how much coffee they drink.
The study found that drinking two or more cups of coffee a day was linked to about twice the risk of death from heart and blood vessel disease among people with severe high blood pressure. In contrast, drinking one cup of coffee a day was not linked to a higher risk, even among people with high blood pressure.
The research was led by Hiroyasu Iso and was published in the Journal of the American Heart Association. It examined the relationship between coffee, green tea, blood pressure and deaths from diseases affecting the heart and blood vessels.
High blood pressure means that blood pushes against the walls of the arteries with too much force. Over time, this can damage blood vessels and increase the risk of heart attack, stroke and other serious health problems.
The researchers were particularly interested in people with readings of 160/100 mm Hg or higher. Blood pressure at this level is considered seriously elevated and already places extra strain on the heart and blood vessels.
The study included more than 18,000 adults in Japan, including over 6,570 men and more than 12,000 women between the ages of 40 and 79. Researchers collected information about how much coffee and green tea the participants drank and followed their health over time.
Participants were also placed into different groups according to their blood pressure. This allowed the researchers to see whether the possible effects of coffee were different for people with normal, mildly raised or severely raised blood pressure.
Among people with the highest blood pressure, those drinking at least two cups of coffee each day had around double the risk of dying from heart and blood vessel disease compared with people who did not drink coffee. This increased risk was not seen in people with lower blood pressure.
The results were also different for people who drank only one cup of coffee a day. That amount was not linked to a higher risk of heart-related death at any blood pressure level examined in the study.
Coffee contains caffeine, which can temporarily increase alertness but can also raise blood pressure in some people. It may also cause a faster heartbeat, sleep problems or feelings of nervousness, especially when consumed in larger amounts or by people who are sensitive to caffeine.
For someone whose blood pressure is already very high, these effects may be more important. The researchers suggested that the harmful effects of larger amounts of caffeine could outweigh some of coffee’s possible benefits in people with severe hypertension.
Green tea produced a different result. Regular green tea drinking was not associated with a higher risk of death from heart and blood vessel disease, even among participants with severe high blood pressure.
Although green tea also contains caffeine, it provides plant substances called polyphenols. These compounds have antioxidant and anti-inflammatory effects, and researchers think they may help explain why green tea did not show the same pattern as heavier coffee consumption.
The study does not prove that drinking coffee directly caused the deaths. It was an observational study, meaning researchers followed people’s habits rather than assigning them to drink different amounts of coffee, so other health and lifestyle differences may have influenced the results.
Still, the findings suggest that the effects of coffee may depend on a person’s existing health. What appears safe or even beneficial for many adults may not have the same effect in someone whose blood pressure is already dangerously high.
People with severe hypertension do not necessarily need to give up coffee completely based on this study alone. However, those who regularly drink several cups a day may want to discuss their caffeine intake with a healthcare professional while continuing to control their blood pressure through appropriate treatment and healthy daily habits.
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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