Researchers said the top and bottom values of a blood pressure reading are both associated with risks of heart attack and stroke.

It is commonly believed that risks of cardiovascular diseases are intimately tied with the systolic blood pressure or the upper part of the blood pressure reading. However, a new study published in the New England Journal of Medicine opined that uncontrolled systolic and diastolic blood pressures are equally harmful.

A team of researchers involved in the large study probed an estimate of 36 million blood pressure readings of 1.3 million Kaiser Permanente patients in North Carolina recorded between 2007 and 2016. They looked for incidences of myocardial infarction, ischemic stroke, hemorrhagic stroke, heart attack, and stroke.

Pendulum Swing

The force of blood flowing in arteries, veins, and capillaries refers to blood pressure. The top number or systolic is the pressure of vessels when the heart beats and pumps out blood. The bottom number or diastolic refers to the residual pressure on the arterial walls when the heart is at rest filling up with blood or in between beats.

"There has been a pendulum-swing over the years toward the view that systolic hypertension is the only thing that matters when it comes to conveying the risk of adverse outcomes like a heart attack or stroke," said Alexander C. Flint, a stroke specialist at Kaiser Permanente and the study's lead author.

Blood pressure levels considered within the normal range is at 120/80 mm Hg while high blood pressure is defined as any measure above 140/90 mm Hg, with 140 mm as the systolic blood pressure and 90 mm as the diastolic pressure. Depending on the patient's condition and medical history, a reading of 130/80 mm Hg can be considered high enough for medical treatment.

Controlling Blood Pressure Levels

The study cites that high systolic pressure poses a greater risk of heart attack and stroke, but an uncontrolled diastolic pressure could also adversely affect overall cardiovascular health. The study also found that patients with a systolic blood pressure of 160 had a 4.8 percent risk of having a heart attack or stroke, while patients with a diastolic blood pressure of 96 had a 3.6 percent risk.

The study suggests that both systolic and diastolic blood pressure levels need to be always in check. If uncontrolled, both measures of blood pressure can raise the risk of heart attacks and strokes.

European guidelines remain at 140/90mm as the definition of hypertension. In 2017, US guidelines for blood pressure were revised, lowering the threshold from 140/90 to 130/80 mm as hypertension.

Having blood pressure that is too low is also dangerous as people with the highest and lowest diastolic blood pressures were the ones who are most at risk for heart attack and stroke. Systolic blood pressures lower than 90 are also harmful and can result in low blood flow and oxygen delivery to vital organs including the brain.