Blood pressure measures the force of circulating blood against artery walls. It is recorded in millimeters of mercury (mmHg) as two numbers: systolic (the top number, measuring force when the heart beats) and diastolic (the bottom number, measuring force when the heart rests between beats). Medical standards for healthy blood pressure are not static and evolve significantly as new research becomes available.
The Standard in 1970
In the late 1960s and early 1970s, the threshold for classifying high blood pressure (hypertension) was considerably higher than it is today. A reading of 140/90 mmHg was often the dividing line between acceptable and high. Many physicians focused primarily on diastolic pressure, reserving treatment for individuals whose diastolic reading consistently measured 100 mmHg or higher. Some medical views tolerated systolic pressures up to 160 mmHg, especially in older patients, without immediate intervention. The prevailing opinion considered a gradual rise in blood pressure with age to be a normal part of the aging process.
Current Blood Pressure Guidelines
The current guidelines, set by organizations like the American Heart Association (AHA) and the American College of Cardiology (ACC), reflect a much lower threshold for defining healthy blood pressure. A reading is now considered normal only if it is less than 120 mmHg systolic and less than 80 mmHg diastolic.
Readings between 120 and 129 mmHg systolic, with a diastolic pressure still below 80 mmHg, are categorized as Elevated. Stage 1 Hypertension is diagnosed when the systolic pressure is between 130 and 139 mmHg or the diastolic pressure is between 80 and 89 mmHg. Stage 2 Hypertension is defined by a systolic reading of 140 mmHg or higher, or a diastolic reading of 90 mmHg or higher.
Drivers Behind the Reclassification
The progressive lowering of the blood pressure standard was driven by decades of compelling epidemiological and clinical trial data. Key longitudinal studies, such as the Framingham Heart Study, demonstrated that the risk for cardiovascular events is continuous. This means damage to the arteries begins at levels previously considered normal.
The Systolic Blood Pressure Intervention Trial (SPRINT) later provided evidence that aggressively lowering systolic pressure to a target below 120 mmHg significantly reduced the rates of cardiovascular events, heart failure, and death. The focus also shifted from diastolic pressure to systolic pressure, which proved to be a stronger predictor of cardiovascular risk, especially in middle-aged and older adults. This evidence compelled medical societies to redefine the categories to better reflect actual cardiovascular risk.
Public Health Implications of Shifting Standards
The reclassification of blood pressure standards immediately resulted in a large increase in the percentage of the population diagnosed with hypertension, especially under the new Stage 1 category. This broader definition means medical professionals are intervening much earlier in the disease process. They often recommend intensive lifestyle modifications for people who would have been told they were fine in 1970.
The goal of this earlier intervention is prevention, aiming to stop the onset of severe, long-term conditions like stroke, heart attack, and kidney damage. By identifying risk earlier, physicians can encourage patients to adopt changes like improved diet and increased physical activity before medication is necessary. For those needing treatment, the lower target ensures a comprehensive effort to reduce the lifetime burden of cardiovascular disease.