Doctor Decoded: Systolic vs. Diastolic Blood Pressure

You know the healthy range for BP numbers … but what do those numbers mean?

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Your doctor reviews the vital signs that the nurse recorded earlier in the appointment. “Hmm, your systolic reading is high,” she says. 

Sys-what?

Your blood pressure consists of two separate numbers: your systolic blood pressure and diastolic blood pressure. Together, the two numbers in a blood pressure reading represent the measure of the force of blood exerted on the artery walls. These readings are crucial for understanding your cardiovascular health, since high blood pressure doesn’t cause symptoms.  

The top number is your systolic blood pressure. This represents the pressure on artery walls when the heart beats. That’s why this number is higher: The blood obviously has more force while it’s being given a push by the heart. 

A “normal” systolic reading is below 120 mm Hg (millimeters of mercury, a way of measuring pressure). This means the heart doesn’t have to work too hard to pump blood throughout the body, so the rest of your body easily receives the oxygen and nutrients it needs to run smoothly. 

Alternatively, if systolic blood pressure is high, that means the heart is working harder to distribute blood, and that extra force on the artery walls can cause damage over time.

Systolic blood pressure tends to rise as you age due to stiffening arteries and plaque buildup, but lifestyle factors and medical history can exacerbate or alleviate this age-related trend. Risk factors for high blood pressure include things like: 

  • Eating a diet high in saturated fat, which can lead to high blood cholesterol levels and plaque buildup

  • Having diabetes with uncontrolled blood sugar levels, which can cause damage to the blood vessels that stiffens the artery walls over time

  • Smoking cigarettes, which can damage, narrow, and harden arteries

The bottom number is your diastolic blood pressure. This measures the pressure on artery walls between heartbeats, while the heart is relaxing to refill with blood. Naturally, this number is lower because the heart is resting, so there’s no active push from a heartbeat. 

A “normal” diastolic reading is below 80 mm Hg. Learn more about healthy ranges for blood pressure numbers here

While both systolic and diastolic blood pressure numbers are important clues about your cardiovascular health, your doctor may show slightly more concern for the top systolic number. That’s because this number is more connected to your risk for heart disease. Learn more about the effects of high blood pressure on your body here.