Heavy coffee drinking may double the heart death risk for people with severe high blood pressure, while green tea shows no such effect.
High blood pressure carries the nickname “silent killer” for a reason. It wears the body down slowly, often without a single warning sign, until the damage is already done. Plenty of people start the morning with a strong coffee to wake up and stay sharp. But research points to a real danger hiding in that habit for anyone living with severe hypertension.
A study published in the Journal of the American Heart Association found that drinking two or more cups of coffee a day may double the risk of dying from cardiovascular disease in people with severe high blood pressure. The same risk did not show up in people who kept their intake to a single cup. It also did not apply to people with milder blood pressure who drank two or more cups. The line, researchers found, was drawn by both how much coffee a person drank and how high their blood pressure already was.
Coffee and High Blood Pressure Death Risk for Heart Disease
The study pulled data from the Japan Collaborative Cohort Study for Evaluation of Cancer Risk, a large project that tracked adults across 45 Japanese communities. Researchers followed more than 18,600 men and women aged 40 to 79. They gathered details through health examinations and questionnaires covering diet, lifestyle, and medical history. Over a median follow-up of nearly 19 years, the team recorded 842 deaths from cardiovascular disease.
Severe high blood pressure was defined as 160/100 mm Hg or higher, which falls into what doctors call grade 2 to 3 hypertension. For people in that group, drinking two or more cups of coffee a day was linked to roughly twice the risk of death from heart disease compared to those who drank none. One cup a day showed no such jump.
Senior author Hiroyasu Iso, a physician and director at Japan’s National Center for Global Health and Medicine, said the goal was to test whether coffee’s known protective effect held up across different degrees of hypertension. According to the researchers, this was the first study to show a link between heavy daily coffee intake and cardiovascular death specifically in people with severe high blood pressure.
The strain comes down to caffeine. A heavy dose pushes heart rate and blood pressure up fast. For healthy people, those short spikes usually do no harm. For someone whose blood pressure is already dangerously high, the extra load can turn deadly. Too much coffee has also been shown to bring on anxiety, heart palpitations, and poor sleep.
Green Tea and Hypertension Show a Different Caffeine Effect
Green tea told a different story. It contains caffeine too, yet the study found no rise in cardiovascular death risk among green tea drinkers at any blood pressure level, including those with severe hypertension.
The researchers pointed to polyphenols as a likely reason. These micronutrients, found in green tea, carry antioxidant and anti-inflammatory properties that help protect blood vessels. The dose of caffeine also differs sharply between the two drinks. According to the U.S. Food and Drug Administration, an 8-ounce cup of green or black tea holds about 30 to 50 milligrams of caffeine, while the same size cup of coffee carries closer to 80 to 100 milligrams.
That gap may help explain why the same stimulant behaves so differently depending on the cup it comes in. Iso said the findings support the idea that people with severe high blood pressure should steer clear of excessive coffee, though he and his team called for more research.
The findings sit against a long line of research praising coffee. Earlier studies have tied one cup a day to a lower death risk after a heart attack and linked regular coffee drinking to reduced odds of conditions like type 2 diabetes and some cancers. Harvard’s School of Public Health has concluded that coffee, on its own, does not raise the risk of heart disease or cancer in most people. The new picture does not erase those benefits. It narrows them, showing where the math flips for one specific group.
Doctors still recommend the same core plan for keeping blood pressure in check. That means prescribed medication, regular exercise, and a heart-healthy diet working together. For people living with severe hypertension, this research adds one simple step. Holding coffee to a single cup a day, or trading it for green tea, may be a small move that does real work in protecting the heart.
