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July 23, 2019

Blood Pressure: Both Numbers Matter

Diastolic pressure, the lower number in a blood pressure reading, is often viewed as insignificant. But new findings say that's far from true.

If you've only been paying attention to the first number in your blood pressure readings, you could be making a serious mistake. A new study of over one million people found that when either number in a blood pressure reading rose, so did a person's chance of heart attack or stroke.

These results held true no matter which reading was chosen as the cutoff line for high blood pressure, 130/80 or 140/90. Newest guidelines set normal blood pressure at or below 120 for the upper (systolic) and 80 or lower for the bottom (diastolic) pressure readings.

While high systolic blood pressure did confer a greater risk than high diastolic blood pressure, a high diastolic blood pressure also significantly raised the risk of heart attack or stroke.

Because the harmful effects of a high systolic (upper) blood pressure have been well documented, patients — and doctors, too —sometimes focus on it exclusively. It has even been suggested that the diastolic (lower) blood pressure reading could be totally ignored.

The current findings strongly argue against doing so.

The study looked at over 1.3 million people and more than 36 million blood pressure readings. People were followed for eight years, and the relationship between their blood pressure readings and whether or not they suffered a heart attack or stroke during those eight years was analyzed.

While high systolic blood pressure did confer a greater risk than high diastolic blood pressure did, a high diastolic blood pressure also raised the risk of heart attack or stroke significantly. Both readings independently influenced risk, meaning that a high diastolic blood pressure should not be ignored.

Systolic pressure — the upper number in a blood pressure reading — measures how hard the heart pumps blood into arteries. Diastolic pressure — the bottom number — measures the pressure on the arteries when the heart rests between beats.

“This research brings a large amount of data to bear on a basic question, and it gives such a clear answer,” said lead author, Alexander C. Flint, a researcher at Kaiser Permanente in Redwood City, California. “Every way you slice the data, the systolic and diastolic pressures are both important.”

According to the authors, the findings also support the 2017 adoption of a lower cutoff point for high blood pressure, anything above 130/80, because in the study, blood pressure readings that were above 130/80 raised a person's heart attack and stroke risk.

An article on the study appears in The New England Journal of Medicine.

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