Almost half of adults in the United States could now be classified as having high blood pressure, after new guidelines from the American Heart Association and the American College of Cardiology have redefined the condition.

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The definition of high blood pressure has been revised, meaning that more Americans are now classified as hypertensive.

Blood pressure is the force by which the blood pushes against the artery walls. High blood pressure, or hypertension, is when this force becomes too high.

Blood pressure is measured in millimeters of mercury, and there are two numbers used to assess blood pressure: systolic and diastolic.

Systolic blood pressure (the top number) is the blood pressure when the heart beats, while diastolic blood pressure (the bottom number) is the blood pressure between heartbeats, when the heart is at rest.

Previous guidelines — established in 2003 — defined hypertension as a blood pressure of 140/90 millimeters of mercury or higher.

Having a blood pressure of between 120/80 millimeters of mercury and 139/89 millimeters of mercury was categorized as prehypertension, whereby blood pressure levels are higher than normal, but are not high enough to be considered hypertensive.

Now, new guidelines from the American Heart Association (AHA) and the American Academy of Cardiology Task Force have revised the definition of hypertension, meaning that millions more adults will be considered at high risk for heart attack, heart disease, stroke, and other cardiovascular problems.

The guidelines were developed by a panel of 21 scientists and health specialists — including Dr. Paul K. Whelton, a representative of the AHA — and they have been 3 years in the making.

Dr. Whelton and co-authors presented the new guidelines at the AHA’s Scientific Sessions 2017, held in Anaheim, CA.

The guidelines have also been published in the journal Hypertension and the Journal of the American College of Cardiology.

Dr. Whelton and colleagues analyzed more than 900 published studies before reaching their new definition of high blood pressure.

Hypertension is now categorized as having a blood pressure of 130/80 millimeters of mercury or higher, while normal blood pressure is categorized as a blood pressure of 120/80 millimeters of mercury.

The term “prehypertension” is also a thing of the past; people with a systolic blood pressure of between 120–129 millimeters of mercury and a diastolic blood pressure below 80 millimeters of mercury are now considered as having “elevated” blood pressure.

Under the new guidelines, individuals in stage 1 of high blood pressure (or having a systolic blood pressure between 130–139 millimeters of mercury or a diastolic blood pressure between 80–89 millimeters of mercury) should have a 10-year risk assessment for heart disease and stroke.

If their risk of these conditions is less than 10 percent, then they should engage in lifestyle changes and be reassessed in 3–6 months. If their risk exceeds 10 percent, lifestyle changes, medication, and monthly follow-up assessments are recommended until blood pressure is under control.

People in stage 2 of high blood pressure (140/90 millimeters of mercury or higher) should adopt lifestyle changes, be treated with at least two medications, and receive monthly follow-ups until blood pressure is controlled, the guidelines state.

A blood pressure exceeding 180/120 millimeters of mercury is categorized as a “hypertensive crisis.” This warrants fast changes to medications, according to the guidelines, or immediate hospitalization if organ damage is identified.

Individuals with normal blood pressure should make healthy lifestyle choices and have their blood pressure checked annually, while those with elevated blood should make healthy lifestyle changes and have their blood pressure assessed every 3–6 months.

Previously, it was estimated that around 1 in 3 adults in the U.S. had high blood pressure.

Under the new guidelines, hypertension now affects 46 percent of the adult U.S. population, which translates to an increase in the use of blood pressure-lowering medications.

According to the AHA, the revised guidelines aim to raise awareness of the risks associated with high blood pressure, and to combat the condition before it leads to bigger health problems.

Dr. Whelton — the lead author of the new guidelines — notes that people with elevated blood pressure and stage 1 hypertension are at high risk of cardiovascular complications, and the new guidelines should help to highlight that risk and encourage people to make changes.

“You’ve already doubled your risk of cardiovascular complications compared to those with a normal level of blood pressure,” he adds.

We want to be straight with people — if you already have a doubling of risk, you need to know about it. It doesn’t mean you need medication, but it’s a yellow light that you need to be lowering your blood pressure, mainly with non-drug approaches.”

Dr. Paul K. Whelton

While the new guidelines will classify more U.S. individuals as hypertensive, the AHA believe that this is not a bad thing.

“Yes, we will label more people hypertensive and give more medication, but we will save lives and money by preventing more strokes, cardiovascular events, and kidney failure,” notes guideline co-author Dr. Kenneth Jamerson, a hypertension specialist at the University of Michigan Health System in Ann Arbor.

“If you are going to put money into the healthcare system,” adds Dr. Jamerson, “it’s to everyone’s advantage if we treat and prevent on this side of it, in early treatment.”