- Researchers report that people with severe hypertension should not drink more than one cup of coffee per day.
- They say high coffee consumption by people with abnormally high blood pressure was associated with double the risk of death from cardiovascular disease.
- The researchers noted, however, that green tea does not produce the same adverse health effects.
A studyTrusted Source published today says people with severe hypertension who drink more than one cup of coffee per day may be doubling their risk of death from cardiovascular disease.
The researchers also found that having one cup of coffee and green tea on the same day wasn’t associated with an increase the risk of death related to cardiovascular disease at any blood pressure measurement, although both drinks contain caffeine.
The Food and Drug Administration saysTrusted Source that an 8-ounce cup of green or black tea has 30 to 50 milligrams of caffeine while an 8-ounce cup of coffee has about 80 to 100 milligrams.
Severe high blood pressure is considered 160/100 mm Hg or higher.
The study, which was published in the Journal of the American Heart Association, looked at more than 6,570 men and more than 12,000 women, ages 40 to 79 years at the start of the research.
Participants came from the Japan Collaborative Cohort Study for Evaluation of Cancer RiskTrusted Source – a large, prospective study established between 1988 and 1990 of adults living in 45 Japanese communities. The data came from health examinations and self-administered questionnaires.
During nearly 19 years of follow-up, researchers documented 842 cardiovascular-related deaths Their analysis found drinking two or more cups of coffee a day was associated with twice the risk of cardiovascular disease death in people with severe hypertension than those who didn’t drink coffee.
They also found drinking one cup of coffee a day wasn’t associated with an increased risk of death from cardiovascular disease across all blood pressure categories.
On the other hand, consuming green tea wasn’t associated with an increased risk of mortality across any blood pressure categories.
“To the best of our knowledge, this is the first study to find an association between drinking two or more cups of coffee daily and cardiovascular disease mortality among people with severe hypertension,” said Dr. Hiroyasu Iso, MPH, the study’s senior author and the director of the Institute for Global Health Policy Research, Bureau of International Health Cooperation, National Center for Global Health and Medicine in Tokyo, in a statement.
Hypertension, also known as high blood pressure,Trusted Source happens when the force of blood pushing against the walls of blood vessels is consistently too high, making the heart work harder to pump blood.
It’s measured in millimeters of mercury (mm Hg). Anything 130/80 mm Hg or higher is considered high blood pressure.
The study’s authors pointed out previous research Trusted Sourcefound drinking one cup of coffee a day may help heart attack survivors and may prevent heart attacks or strokes in healthy individuals.
Coffee may help reduce the risk of developing chronic illnesses, such as type 2 diabetes and some cancers.
“Coffee’s beneficial effects may center around its anti-inflammatory effects including reduction in oxidative stress on the blood vessels, improved insulin sensitivity, and inhibition of stomach absorption of fat,” Dr. Guy L. Mintz, the director of cardiovascular health and lipidology at Sandra Atlas Bass Heart Hospital in Manhasset, New York, told Healthline.
“The group with severe hypertension may be at greater risk simply because they cannot tolerate even a short time further increase in blood pressure that caffeine might cause,” Mintz added. “Caffeine may affect sleep patterns limiting the amount of sleep a person may get. Less sleep has been associated with an increased risk of myocardial infarctions and cardiovascular death.
Mintz told Healthline caffeine can also cause constriction of blood vessels causing even higher blood pressure or increasing the work of the heart.
Mintz said green tea doesn’t have the same effect as coffee.
“Benefits of green tea are well known,” he said. “The anti-inflammatory effects of polyphenols and flavonoids lead to improvement in blood vessel function with more dilation and less constriction, improvement in blood pressure, increase in HDL good cholesterol and reduction in other inflammatory cells.”
“These positive vascular effects may overcome any deleterious effects of caffeine,” he added.
Veronica Rouse is a registered dietitian and certified diabetes educator who specializes in cardiac nutrition. She told Healthline green tea is an important aspect of the green Mediterranean diet.
“It is suggested that the polyphenols found in green tea are micronutrients that are protective against free radicals,” Rouse said. “Free radicals are compounds that can cause damage to our cells. Thus, consuming polyphenols is crucial to reducing the cell damage that can lead to chronic diseases like heart disease.”
Rouse noted that the polyphenols in coffee aren’t the same ones found in green tea.
“The way coffee is prepared and the type of coffee used in research studies varies, which can explain why there are so many mixed conclusions and inability to identify types of polyphenols in coffee and their effects,” Rouse said.
Caffeine may not be the only less-than-healthy substance in coffee, Dr. Enrique Garcia-Sayan, a cardiologist with UTHealth Houston, told Healthline.
“Some studies show that even decaffeinated coffee can transiently elevate blood pressure,” Garcia-Sayan said. “But the biggest question is whether this transient elevation in blood pressure can harm overall health, as coffee contains various substances beyond caffeine, which may have antioxidant effects and significant health benefits.”
Garcia-Sayan added that coffee is a complex beverage containing numerous substances with antioxidant properties that may protect the human body from oxidative damage and chronic illnesses.
“However, these benefits must be balanced against issues that may arise with excessive coffee consumption, including anxiety, insomnia, palpitations, and elevation in blood pressure,” he noted. “Furthermore, much of the benefits may be negated by adding sugar and dairy fat, as is common in commercial coffee-based drinks.”