The new guidelines lowered the blood pressure range of what is considered normal. That means people whose blood pressure used to be considered high normal or prehypertension now will be considered elevated blood pressure or stage 1 hypertension.
The American College of Cardiology and the American Heart Association estimate the change will affect more than 31 million Americans.
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Under the old guidelines from 2003, top line, or systolic, blood pressure levels under 120 were considered normal and levels between 120 and 140 were considered high normal or prehypertension.
Under the new guidelines, under 120 is still normal, but 120 to 129 is considered elevated blood pressure.
The new guidelines say people with elevated blood pressure should make lifestyle changes, like getting more exercise and eating less salt.
"The main difference is that high blood pressure, stage 1 hypertension, starts at 130," Dr. Sandra Taler, a Mayo Clinic nephrologist, says. "So 130 to 139 systolic, 80 to 89 diastolic would be stage 1 hypertension."
Dr. Taler says that range used to be considered high normal. She helped write the new guidelines and says people with stage 1 hypertension may need blood pressure-lowering medication in addition to lifestyle changes.
"And then at 140 systolic and 90 diastolic, that's now stage 2," Dr. Taler says.
With stage 2 hypertension, Dr. Taler says people should be taking blood pressure medications.
She says lowering what is considered normal will help people address blood pressure problems sooner, and lower their risk of cardiovascular problems and early death.