For most adults, the top number (systolic) is the more important predictor of heart disease, stroke, and other cardiovascular problems. This is especially true after age 50, when systolic pressure becomes the dominant risk factor. But the bottom number (diastolic) still matters, particularly for younger adults, and both numbers together give the most complete picture of your cardiovascular health.
What Each Number Measures
Your blood pressure reading has two numbers for a reason: they capture two different moments in your heart’s pumping cycle. The top number, systolic pressure, is the peak force against your artery walls when your heart contracts and pushes blood out. The bottom number, diastolic pressure, is the lowest pressure between beats, when your heart relaxes and refills with blood.
Normal blood pressure is below 120/80 mmHg. The 2025 guidelines from the American Heart Association and American College of Cardiology classify readings of 130 to 139 systolic or 80 to 89 diastolic as stage 1 hypertension, and anything at or above 140/90 as stage 2. Notice that either number being elevated is enough to qualify as hypertension.
Why Systolic Pressure Gets More Attention
Systolic blood pressure rises steadily with age as arteries become stiffer and less elastic. This stiffening means the arteries can’t absorb the force of each heartbeat as well as they once did, so the peak pressure climbs. Diastolic pressure, by contrast, tends to rise until about age 55 and then actually starts to fall. That’s why older adults commonly have a pattern like 150/70, with a high top number and a normal or low bottom number.
This pattern, called isolated systolic hypertension, is the most common form of high blood pressure in older adults. It raises the risk of stroke, heart disease, dementia, and chronic kidney disease over time. In a Framingham Heart Study analysis, knowing only the systolic blood pressure correctly classified the stage of hypertension in 99% of adults over 60. Knowing only the diastolic number got the classification right just 66% of the time.
The link between systolic pressure and specific outcomes is striking. In patients over 50 with uncontrolled hypertension, each 1 mmHg increase in systolic pressure was associated with roughly a 4% increase in both 5-year and 10-year stroke risk. Diastolic pressure showed no significant correlation with stroke risk in the same group. For heart failure, data from the Framingham study found that a 20 mmHg increase in systolic pressure raised the risk of developing heart failure by 56%.
When Diastolic Pressure Matters Most
If you’re under 50, don’t ignore the bottom number. In younger adults, both systolic and diastolic blood pressure independently predict cardiovascular risk. A large study of nearly 285,000 adults aged 18 to 39 found that isolated diastolic hypertension (a normal top number but an elevated bottom number) doubled the risk of cardiovascular death compared to people with normal blood pressure. At stage 2 levels, the risk was nearly three times higher.
This makes sense physiologically. In younger people, high diastolic pressure often reflects increased resistance in the smaller blood vessels throughout the body. It can signal early vascular problems that, left untreated, lead to damage over decades. So while systolic pressure dominates the conversation in older populations, diastolic pressure is a meaningful warning sign in younger ones.
The Gap Between the Two Numbers
The difference between your systolic and diastolic readings is called pulse pressure. If your blood pressure is 140/80, your pulse pressure is 60. This gap serves as a rough indicator of arterial stiffness. A widening pulse pressure, where systolic climbs while diastolic stays flat or drops, signals that arteries are losing their flexibility.
In the Framingham data, a 16 mmHg increase in pulse pressure raised the risk of heart failure by 55%, nearly identical to the risk from rising systolic pressure alone. A wide pulse pressure is particularly common in older adults and adds useful information beyond what either number provides individually. If your top number is climbing while your bottom number is dropping, that pattern itself is worth paying attention to.
The Risk of Diastolic Pressure That’s Too Low
There’s an important wrinkle in blood pressure management. Your heart muscle receives its own blood supply primarily during the diastolic phase, when the heart is relaxed between beats. If diastolic pressure drops too low, the heart may not get enough oxygen-rich blood. This creates what researchers call the J-curve effect: cardiovascular risk drops as blood pressure comes down, but at very low diastolic levels, risk can start creeping back up.
This is most relevant for people taking blood pressure medication. Aggressively lowering systolic pressure sometimes pulls diastolic pressure down to levels that could compromise blood flow to the heart. It’s one reason doctors monitor both numbers during treatment, even when systolic pressure is the primary target.
Both Numbers, One Picture
Medical consensus has shifted clearly toward systolic blood pressure as the primary treatment target, reversing decades of emphasis on diastolic pressure. But the most accurate risk prediction comes from considering both numbers together. A person with a reading of 150/95 faces different risks than someone at 150/70, even though the systolic number is the same.
The practical takeaway: if you’re over 50, your systolic number deserves the most attention and is the single strongest predictor of cardiovascular events. If you’re younger, an elevated diastolic reading is a legitimate health concern even when your systolic number looks fine. And regardless of age, if either number falls into the hypertension range, the reading qualifies as high blood pressure and carries real risk.