Both Blood Pressure Numbers Matter, New Study Finds

Decades of advice are overturned, doubling the number of numbers to worry about.

Robert Roy Britt
Jul 18, 2019 · 3 min read

As if understanding blood pressure wasn’t confusing enough, a new study suggests doctors and patients need to relearn half of what had been the common wisdom. For decades, health professionals have instructed people to worry about the upper number, called the systolic reading, and not to worry too much about the lower number, called the diastolic reading.

Worry about both, researchers now say. The results affect nearly half of U.s. adults who, by current definitions, have high blood pressure.

The change is based on a review of more than 36 million blood-pressure readings from 1.3 million people and their health outcomes over time—the largest study of its kind, the researchers say.

“This research brings a large amount of data to bear on a basic question, and it gives such a clear answer,” said the study’s lead author Alexander Flint, a stroke specialist at Kaiser Permanente, a conglomerate that runs hospitals and offers health plans. “Every way you slice the data, the systolic and diastolic pressures are both important.”

Systolic pressure, the upper number, measures how hard the heart works.

Diastolic pressure measures the pressure on the arteries as the heart rests between beats.

Until now, some experts were still arguing “that the diastolic number might reasonably be ignored,” Flint said. High systolic pressure does have a greater impact on negative health outcomes, the study finds, but “both systolic and diastolic pressures strongly influenced the risk of heart attack or stroke.” And that’s true whether the measurements are 140/90 or 130/80, meaning anything at those levels or higher is cause for concern.

The findings, detailed in the July 18 issue of the New England Journal of Medicine, are seen as confirming the recently revised minimum threshold for high blood pressure, also called hypertension.

In 2017, the American College of Cardiology and American Heart Association announced new, lower numbers (130/80) as the threshold for hypertension, versus the previous minimum threshold of 140/90. “The change means 46 percent of U.S. adults are identified as having high blood pressure, compared with 32 percent under the previous definition,” the groups said in a statement at the time.

“Controversy has long persisted about whether systolic blood pressure, diastolic blood pressure, or both contribute to cardiovascular risk,” Deepak Bhatt, a professor of medicine at Harvard Medical School and one of the leaders of the new study. “This analysis using a very large amount of longitudinal data convincingly demonstrates that both are important, and it shows that in people who are otherwise generally healthy, lower blood pressure numbers are better.”

Other health professionals have said the study makes sense. “This is something I’ve believed for years, that we should treat both systolic and diastolic blood pressure,” Angela Brown, an associate professor of medicine and clinical hypertension specialist at Washington University School of Medicine in St. Louis, told NBC News.

In a person with hypertension, the force of blood pushing against vessel walls is too high, the American Heart Association explains. “This added pressure causes the heart to work too hard and blood vessels to function less effectively. Over time, the stress damages the tissues within arteries, which can further damage the heart and circulatory system.”

Without any symptoms alerting a person, hypertension can lead to heart disease, the leading cause of death in the United States.

All other things being equal, blood pressure tends to rise as we age. Medications are just one of many ways to lower blood pressure. Deep breathing and other relaxation techniques have been shown to be effective, along with an improved diet, moderate to vigorous exercise, and simply taking a walk or even just being in nature.

Health experts advise anyone with hypertension—a BP of 130/80 or higher—consult with a doctor.

Credit: The American Heart Association

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Robert Roy Britt

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Explainer of things, former editor-in-chief of Live Science and Space .com, author of the science thriller “5 Days to Landfall.”

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