Blood Pressure from Top to Bottom


Fifty years ago, diastolic pressure—the bottom number in your blood pressure reading—was considered a primary measure of heart health. Over time, newer research revealed systolic pressure—the top number—as a better predictor of heart concerns. That’s why, by the early 2000s, the pendulum had swung the other way, with a “near-exclusive” focus on systolic high blood pressure, according to a study earlier this year in The New England Journal of Medicine. But some researchers are wondering if the pendulum has swung too far.

Age and blood pressure
In 2017, the American College of Cardiology and American Heart Association updated blood pressure guidelines, which doctors use to diagnose and treat the condition, redefining high blood pressure to a lower threshold of 130 mmHg (millimeters of mercury) for systolic blood pressure and 80 mmHg for diastolic blood pressure. Doctors tend to pay more attention to systolic blood pressure than diastolic in people over 50. That’s because, for most people, increasing stiffness in the arteries, plaque buildup, and cardiac and vascular disease cause systolic pressure to rise. Systolic blood pressure, which measures the pressure of your blood against artery walls when your heart beats, is considered normal when it’s lower than 120 mmHg.

Diastolic blood pressure measures the pressure of blood against artery walls while your heart is at rest. Normal diastolic pressure is lower than 80 mmHg. Unlike systolic pressure, diastolic pressure typically peaks around age 50 and gradually decreases with age.

Don’t ignore diastolic pressure
So how critical is diastolic blood pressure in predicting heart health? To find out, researchers at Kaiser Permanente health system, based in Oakland, Ca., assessed the blood pressure and health data of more than 1.3 million patients (average age, 53) over eight years. They found that elevated systolic and diastolic blood pressure each had an independent effect on cardiovascular health. Both were associated with an increased risk of heart attack and stroke.

Even people who had normal systolic readings but high diastolic ones were still at risk. However, elevated systolic pressure is still considered more dangerous than elevated diastolic pressure. The study authors say that doctors should consider both systolic and diastolic pressure when treating high blood pressure, pushing back against some experts who suggest eliminating diastolic pressure from treatment considerations.

Interestingly, diastolic readings below 60 mmHg were associated with poor cardiovascular outcomes. The risk wasn’t as prominent, though, when the researchers took into account age and other risk factors.

Still, low diastolic readings are of concern, especially with regard to the revised 2017 treatment guidelines. In addition to redefining what constitutes high blood pressure, the guidelines recommended lower blood pressure targets when treating the condition. Consequently, aggressive treatment to drive down high systolic pressure could be lowering diastolic pressure to undesirable levels.

Can you go too low?
A Johns Hopkins study published in 2016 in the Journal of the American College of Cardiology suggests that low diastolic pressure may be associated with damage to heart tissue. The researchers cautioned, however, that more evidence is needed before a direct correlation between the two can be made.

That said, they hypothesize that very low diastolic pressure may result in inadequate pumping action through the coronary arteries that nourish the heart muscle. In their study of more than 11,000 people (average age, 57), the researchers found that those who had a diastolic reading of 60 mmHg or lower were more at risk for coronary heart disease, heart failure, and premature death than people who had normal readings for both diastolic and systolic pressure. What’s more, a systolic blood pressure of 120 mmHg or more had a greater impact on health in people who had lower diastolic pressure. Based on these findings, the study advises doctors to try to keep diastolic blood pressure levels from falling below 70 mmHg and more so below 60 mmHg.

What should you do in light of these findings? Pay attention to blood pressure measurements taken at your doctor’s office and ask about any high diastolic reading, especially if your systolic pressure is normal. If you’re taking an antihypertensive drug and you experience any symptoms of low blood pressure, such as lightheadedness, nausea, blurred vision, or fainting, let your doctor know. He or she may need to modify your medications.