The guidelines are being published by the American Heart Association (AHA) and the American College of Cardiology (ACC) for detection, prevention, management and treatment of high blood pressure.
Rather than one in three US adults having high blood pressure (32 per cent) with the previous definition, the new guidelines will result in nearly half of the US adult population (46 per cent) having high BP, or hypertension, AHA said in a statement.
High blood pressure is now defined as readings of 130 millimetres of mercury (mm Hg) and higher for the systolic BP measurement, or readings of 80 and higher for the diastolic measurement.
That is a change from the old definition of 140/90 and higher, reflecting complications that can occur at those lower numbers.
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The new guidelines stress the importance of using proper technique to measure blood pressure. Blood pressure levels should be based on an average of two to three readings on at least two different occasions, AHA said.
It is known as the "silent killer" because often there are no symptoms, despite its role in significantly increasing the risk for heart disease and stroke.
Paul K Whelton, lead author of the guidelines published in the journal Hypertension and the Journal of the American College of Cardiology, noted the dangers of blood pressure levels between 130-139/80-89 mm Hg.
"You have already doubled your risk of cardiovascular complications compared to those with a normal level of blood pressure," Whelton said.