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Q. When I am monitoring my blood pressure, which number is most important — top, bottom, or both?
A. While both numbers in a blood pressure reading are essential for diagnosing and treating high blood pressure, doctors primarily focus on the top number, also known as systolic pressure.
Systolic pressure reflects the force produced by the heart when it pumps blood out to the body, while diastolic blood pressure (the bottom number) is the pressure in your blood vessels when the heart is at rest.
Over the years, research has found that both numbers are equally important in monitoring heart health. However, most studies show a greater risk of stroke and heart disease related to higher systolic pressures compared with elevated diastolic pressures. That's especially true in people ages 50 and older, which is why doctors tend to monitor the top number more closely. The reason for the difference in risk may be related to the force put on the arteries when blood rushes out of the heart.
The American Heart Association now defines high blood pressure as 130/80 mm Hg or higher. The new guidelines recommend you check your blood pressure often, ideally with a home monitor, to help your doctor determine if you need to make lifestyle changes, begin medication, or alter your current therapy.
— by Howard LeWine, M.D.
Editor in Chief, Harvard Men's Health Watch
As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles.
No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.
Blood pressure is a measure of the force that your heart uses to pump blood around your body. Blood pressure is measured in millimetres of mercury (mmHg) and is given as 2 figures: For example, if
your blood pressure is "140 over 90" or 140/90mmHg, it means you have a systolic pressure of 140mmHg and a diastolic pressure of 90mmHg. As a general guide: High blood pressure is often related to unhealthy lifestyle habits, such as smoking, drinking too much alcohol, being overweight and not exercising enough. Left untreated, high blood pressure can increase your risk of developing a number of serious long-term health conditions, such as coronary heart disease and kidney disease. Low blood pressure is less common. Some medicines can cause low blood pressure as a side effect. It can also be caused by a number of underlying conditions, including heart failure and dehydration. Page last reviewed: 17 September 2019How is blood pressure measured?
High blood pressure
Low blood pressure
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review due: 17 September 2022
If you are diagnosed with high blood pressure, talk with your health care team about your blood pressure levels and how these levels affect your treatment plan.
What are the signs and symptoms of high blood pressure?
High blood pressure usually has no warning signs or symptoms, and many people do not know they have it. Measuring your blood pressure is the only way to know whether you have high blood pressure.
What causes high blood pressure?
High blood pressure usually develops over time. It can happen because of unhealthy lifestyle choices, such as not getting enough regular physical activity. Certain health conditions, such as diabetes and having obesity, can also increase the risk for developing high blood pressure. High blood pressure can also happen during pregnancy.
You can manage your blood pressure to lower your risk for serious health problems that may affect your heart, brain, kidneys, and eyes.
What problems does high blood pressure cause?
High blood pressure can damage your health in many ways. It can seriously hurt important organs like your heart, brain, kidneys, and eyes.
The good news is that, in most cases, you can manage your blood pressure to lower your risk for serious health problems.
Heart Attack and Heart Disease
High blood pressure can damage your arteries by making them less elastic, which decreases the flow of blood and oxygen to your heart and leads to heart disease. In addition, decreased blood flow to the heart can cause:
- Chest pain, also called angina.
- Heart attack, which happens when the blood supply to your heart is blocked and heart muscle begins to die without enough oxygen. The longer the blood flow is blocked, the greater the damage to the heart.
- Heart failure, a condition that means your heart can’t pump enough blood and oxygen to your other organs.
Stroke and Brain Problems
High blood pressure can cause the arteries that supply blood and oxygen to the brain to burst or be blocked, causing a stroke. Brain cells die during a stroke because they do not get enough oxygen. Stroke can cause serious disabilities in speech, movement, and other basic activities. A stroke can also kill you.
Having high blood pressure, especially in midlife, is linked to having poorer cognitive function and dementia later in life. Learn more about the link between high blood pressure and dementia from the National Institutes of Health’s Mind Your Risks® campaign.
Kidney Disease
Adults with diabetes, high blood pressure, or both have a higher risk of developing chronic kidney disease than those without these conditions.
How do I know if I have high blood pressure?
There’s only one way to know if you have high blood pressure: Have a doctor or other health professional measure it. Measuring your blood pressure is quick and painless.
Talk with your health care team about regularly measuring your blood pressure at home, also called self-measured blood pressure (SMBP) monitoring.
High blood pressure is called the “silent killer” because it usually has no warning signs or symptoms, and many people do not know they have it.
What can I do to prevent or manage high blood pressure?
Many people with high blood pressure can lower their blood pressure into a healthy range or keep their numbers in a healthy range by making lifestyle changes. Talk with your health care team about
- Getting at least 150 minutes of physical activity each week (about 30 minutes a day, 5 days a week)
- Not smoking
- Eating a healthy diet, including limiting sodium (salt) and alcohol
- Keeping a healthy weight
- Managing stress
Learn more about ways to manage and prevent high blood pressure.
In addition to making positive lifestyle changes, some people with high blood pressure need to take medicine to manage their blood pressure. Learn more about medicines for high blood pressure.
Talk with your health care team right away if you think you have high blood pressure or if you’ve been told you have high blood pressure but do not have it under control.
By taking action to lower your blood pressure, you can help protect yourself against heart disease and stroke, also sometimes called cardiovascular disease (CVD).