For a long time, normal blood pressure was defined as 120/80 (systolic / diastolic). Recently, the American Heart Association changed the definition of normal blood pressure to Less than 120 / Less than 80.
This redefinition was enacted because of ongoing research examining the long term health effects of different blood pressures. Along with redefining the normal value, the new American Heart Association guidelines changed the cutoff values for the different stages of high blood pressure. Again, these changes were also based on new research which more clearly shows the increasing risk of heart attack and other illness as the blood pressure rises.
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