The American Heart Association and the American College of Cardiology just lowered the threshold for high blood pressure to 130/80 millimeters of mercury, and now 46% of Americans - up from 32% - fall in the danger zone.
Harlan Krumholz, a cardiologist at Yale University, said the new definition will radically change how primary care doctors interact with their patients.
"We know that high blood pressure is one of the major causes of heart attack and strokes", said Dr. David Shearer, Family Medicine Physician, SSM Health.
Tighter blood pressure guidelines from US heart organizations mean millions more people need to make lifestyle changes, or start taking medication, in order to avoid cardiovascular problems.
"I think the goal of the new guidelines is to get blood pressure on the radar for those at-risk patients, to make the diagnosis, to get them to do some lifestyle changes".More news: Qualcomm 'set to reject' Broadcom takeover offer
Healthy lifestyle changes include losing weight, exercising more, eating healthier, not smoking, avoiding alcohol and salt, and reducing stress.
The normal limit for blood pressure is considered 120 for systolic, or how much pressure the blood places on the artery walls when the heart beats, and 80 for diastolic, which is measured between beats.
But patients in the 120 systolic blood pressure group had a higher rate of kidney injury or failure, as well as fainting. "So the earlier, the better", said Dr. Shearer.
Damage to blood vessels is already beginning once blood pressure reaches 130/80, said the guidelines, which were based in part on a major U.S. government-funded study of over 9,000 people nationwide. It measures the amount of pressure going through your heart when it's pumping.
The new guidelines eliminate the prehypertension category. Then a person's reading becomes the average of those numbers and reduces the risk of "white coat hypertension" - blood pressure readings that are improperly elevated because a patient in a doctor's office is nervous. The association recommends that those with stage 1 hypertension will only be prescribed medication if they have a heart attack or stroke.