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Blood pressure: Both numbers matter

Close-up of a blood pressure cuff on a patient's arm with a provider's hand nearby.

Aug. 6, 2019—Every blood pressure reading comes with two numbers, such as 120/80 mm Hg. Systolic pressure—the top number—measures how hard the heart pumps blood into the arteries. Diastolic pressure—the bottom number—measures the pressure on the arteries when the heart rests between beats.

Together they tell a story about your heart health. But that second number sometimes gets shrugged off by risk assessment tools. Now a new study of more than a million people confirms that both numbers matter if you want to protect your health.

Heart-healthy from top to bottom

Past studies have shown that, of the two parts of a blood pressure reading, high systolic pressure was more likely to result in a heart attack or stroke. As a result, doctors have often focused on the first number and ignored the second.

But a recent study suggests they're both important.

It looked at more than 36 million blood pressure readings from 1.3 million people. Like other studies, it found that high systolic pressure was a stronger risk factor for heart attack or stroke. But a high diastolic pressure number also raised both risks significantly.

That was true no matter how high blood pressure was defined: as 140/90 (according to older guidelines) or as 130/80 (according to newer guidelines from the American College of Cardiology and American Heart Association).

The takeaway: It's crucial to work with your doctor to keep both blood pressure numbers in a healthy range.

The study appeared in The New England Journal of Medicine.

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