For most healthy adults, a daily cup or two of coffee appears to be safe, and some research even links moderate coffee drinking to a lower risk of heart disease. But a large study from Japan suggests the picture may be different for people with very high blood pressure.

How the study worked

Researchers analyzed data from more than 18,600 adults in Japan aged 40 to 79 who were part of a long-running health study. Participants filled out questionnaires about their diet, lifestyle and medical history, including how much coffee and green tea they drank, and had health exams that included blood pressure measurements. The researchers then followed them for many years to track deaths from heart disease and stroke. The findings were published in the Journal of the American Heart Association.

Participants were grouped by blood pressure, from normal to “grade 3” or severe hypertension, which means a reading of 160/100 mm Hg or higher.

What the researchers found

• In people with severe high blood pressure, drinking two or more cups of coffee a day was linked to about twice the risk of dying from heart disease or stroke, compared with not drinking coffee.
• One cup a day was not linked to higher risk in any group.
• For people with normal or mildly high blood pressure, coffee was not linked to higher risk.
• Green tea was not linked to higher risk at any blood pressure level.

This was an observational study, so it shows an association rather than proof that coffee caused the deaths. The researchers suggested that the effects of caffeine on blood pressure may outweigh coffee’s potential benefits in people whose blood pressure is already very high.

Why coffee and tea might differ

Coffee contains roughly two to three times as much caffeine per cup as green tea. According to the U.S. Food and Drug Administration, an 8-ounce cup of coffee has about 80 to 100 mg of caffeine, while the same amount of green or black tea has about 30 to 50 mg. Caffeine can cause short-term rises in blood pressure, and green tea also contains compounds called polyphenols that may have heart benefits.

What this means for you

• Know your numbers. Many people with high blood pressure don’t know they have it. Check it regularly at home, at a pharmacy or at your doctor’s office.
• If your blood pressure is very high, ask about caffeine. Talk with your doctor about whether you should limit coffee or switch to decaf or tea.
• Watch total caffeine. Energy drinks, sodas and some pain relievers also contain caffeine. The FDA cites 400 mg a day as an amount not generally linked to harm for most healthy adults, but your safe amount may be lower.
• Focus on proven blood pressure habits. Reduce salt, eat more fruits and vegetables, stay active, limit alcohol, manage stress and take prescribed medications as directed.
• Notice how you feel. A racing heart, jitteriness or trouble sleeping can be signs you’re getting too much caffeine.

Who can probably keep their coffee

For people with normal blood pressure or mild hypertension, this study found no added risk from coffee. Many large studies suggest moderate coffee drinking is part of a healthy diet for most adults. As always, people who are pregnant or have heart rhythm problems should follow their doctor’s advice on caffeine.

The bottom line

In people with severe high blood pressure, two or more cups of coffee a day was linked to a higher risk of dying from heart disease or stroke. If your blood pressure is very high, it’s worth talking with your doctor about cutting back.

This article is for general information and isn’t medical advice. Talk with your healthcare provider about your individual needs.

Sources

• Teramoto M, et al. Coffee and green tea consumption and cardiovascular disease mortality among people with and without hypertension. Journal of the American Heart Association, 2022.
• American Heart Association News: People with very high blood pressure may want to go easy on the coffee, 2022.
• U.S. Food and Drug Administration: Spilling the beans: How much caffeine is too much?