When someone checks your blood pressure, the result usually appears as two numbers, such as 120 over 80.
Many people pay most attention to the top number, but a large study shows that the bottom number can also provide important information about heart and stroke risk.
The top number is called systolic blood pressure. It measures the pressure inside the arteries when the heart contracts and pushes blood around the body.
The bottom number is called diastolic blood pressure. It measures the pressure that remains in the arteries while the heart relaxes between beats.
For many years, doctors placed greater emphasis on systolic pressure, particularly in middle-aged and older adults. That made sense because high systolic pressure has a strong connection with heart attacks, strokes and other problems involving the heart and blood vessels.
But researchers wanted to know whether diastolic pressure still mattered when systolic pressure was taken into account. To investigate, researchers at Kaiser Permanente studied an enormous collection of blood pressure readings from adults in Northern California.
The study included about 1.3 million adults and more than 36 million blood pressure measurements. The information covered roughly nine years, giving researchers a detailed picture of how blood pressure was connected with later health problems.
The researchers compared people’s blood pressure readings with their risk of serious events such as heart attacks and strokes. They found that higher systolic pressure was strongly linked to greater risk, as expected.
However, higher diastolic pressure was independently linked to increased risk as well. In other words, the bottom number still provided useful information even after researchers considered the effect of the top number.
Systolic pressure remained the stronger predictor overall. But the results challenged the idea that diastolic pressure can simply be ignored when doctors and patients assess blood pressure.
The pattern remained when the researchers used different definitions of high blood pressure. This included the older threshold of 140/90 mmHg as well as the lower 130/80 mmHg threshold used in some current guidelines.
High blood pressure is especially important because it often causes no warning signs. A person can feel perfectly healthy while increased pressure is slowly damaging arteries, the heart, brain, kidneys and other organs.
Over time, high pressure can make blood vessels less healthy and increase the chance that they will become narrowed, blocked or damaged. This is one reason regular blood pressure checks can be valuable even for people who feel well.
The findings do not mean that everyone should try to reach exactly the same blood pressure. A person’s ideal target can depend on age, overall health, other medical conditions and medicines, so readings should be discussed with a healthcare professional.
People checking their blood pressure at home should also remember that a single unusual reading does not necessarily mean they have hypertension. Blood pressure naturally changes during the day and can be affected by exercise, stress, caffeine, illness and even how a person is sitting during the measurement.
If blood pressure remains high, lifestyle changes can often help. Regular physical activity, eating less salt, maintaining a healthy weight, not smoking and limiting alcohol can lower risk, while some people also need blood pressure medicine.
The study was led by Dr. Alexander C. Flint and colleagues and published in the New England Journal of Medicine. Its message is straightforward: when it comes to blood pressure, both numbers deserve attention.
Copyright © 2026 Knowridge Science Report. All rights reserved.
