Systolic vs diastolic: which number matters more

Systolic (the top number) is the pressure while the heart beats. Diastolic (the bottom number) is the pressure between beats. In a study of 1.3 million adults both predicted heart attack and stroke, and systolic predicted them more strongly. Whichever number falls in the higher category sets your category.

What 120 over 80 means

Both numbers are pressures in millimeters of mercury, written as mmHg.

The categories work on both numbers at once. For an average of 128/82, systolic alone would be elevated and diastolic alone would be stage 1, so the result is stage 1 in the US chart. See where any pair lands on the chart or the checker.

Which one matters more

Both numbers count. The biggest modern study followed about 1.3 million adults in Northern California for 8 years. High systolic and high diastolic pressure each predicted heart attack and stroke on their own, even after the researchers took the other number into account. For each step up the scale, the risk went up by 18 percent for systolic and 6 percent for diastolic (hazard ratios of 1.18 and 1.06), so systolic had the bigger effect.

An older study pooled data on about one million adults and found a simple ratio between the two. At ages 40 to 69, a 20 point difference in systolic, or roughly a 10 point difference in diastolic, went with about double the rate of death from heart disease and stroke, so a 10 point change in diastolic counted for as much as a 20 point change in systolic.

Age changes the answer

The Framingham Heart Study followed 6,539 adults aged 20 to 79 for 20 years and found that the number that best predicts heart disease shifts gradually with age.

Later researchers have questioned how much pulse pressure adds after 60. The pulse pressure finding comes from this one study, so keep the systolic number as your main guide.

The shift follows how the numbers move over a lifetime. From about age 30 to 50, systolic and diastolic rise together. After about 60, systolic tends to keep climbing while diastolic falls, and the gap widens. The usual explanation is that arteries get stiffer, and it’s why 150/70 is common in older adults. A diastolic of 70 doesn’t make 150/70 any safer, because systolic is well into stage 2.

The patterns, by name

Isolated diastolic hypertension is the pattern with the weakest evidence for added risk. The 2017 US definition counts it as a diastolic of 80 or more with a systolic under 130. In a large 2020 analysis, researchers looked at people who fit that definition and found no significant rise in their risk of cardiovascular death (a hazard ratio of 0.94). That’s an average across groups, though, and it doesn’t mean you’re in the clear, especially if your diastolic is higher. If your average stays high, the page on lowering diastolic pressure lists what helps and what a doctor may check.

Pulse pressure

To get it, subtract diastolic from systolic, so 120/80 gives 40 and 150/70 gives 80. A wide gap in an older adult often points to stiffer arteries, and your doctor can tell you what your own gap means. Systolic is still the one to act on.

Do the same habits move both?

Yes, and usually systolic drops more. Researchers who reviewed 270 exercise trials found these drops:

The full list of things that lower blood pressure is in the how-to.

Measure both, every time

A home cuff gives you both numbers, so keep an average of each. Do a seven-day home week and put the numbers into the home average tool. Bring both averages to your doctor, and never change a medication based on either one by yourself.

If you have chest pain, shortness of breath, back pain, weakness, numbness, vision change or trouble speaking, call emergency services, whatever the number. If your systolic is 180 or higher, or your diastolic is 120 or higher, and you have no symptoms, follow the emergency steps.