What does it mean when the diastolic number is high

Ask the doctor

A. This question comes up often, perhaps because doctors and patients alike tend to pay more attention to the top (first) number, known as systolic pressure. It reflects the amount of pressure inside the arteries as the heart contracts. The bottom (second) number, diastolic pressure, is always lower since it reflects the pressure inside the arteries during the resting phase between heartbeats.

As it turns out, both systolic and diastolic blood pressure are important. Per the most recent guidelines, you have what's called elevated blood pressure if your systolic blood pressure reading is 120 to 129 mm Hg (which stands for millimeters of mercury). Once your systolic reading reaches 130 or higher or your diastolic reading is 80 or higher, you're considered to have high blood pressure, or hypertension.

Most people have what's known as essential or primary hypertension, which means it's not caused by a medical condition, medication, or substance. Primary hypertension can affect both systolic and diastolic pressure to a similar degree. But sometimes, especially in older people, it affects mainly the systolic pressure; this is called isolated systolic hypertension.

Why does this happen? As you age, your arteries tend to become less elastic and less able to accommodate surges of blood. Blood flowing through your arteries at high pressure can damage the inner lining of these vessels, accelerating the buildup of cholesterol-laden plaque. This further stiffens and narrows the arteries, a condition known as atherosclerosis. Because the same volume of blood has to pass through a smaller area, the systolic pressure tends to rise, while the diastolic pressure remains the same or gradually falls over time. In some people with isolated systolic hypertension, the diastolic pressure reading may drop into the 50s or even the 40s.

Most studies show a greater risk of cardiovascular disease (especially strokes) related to high systolic pressure as opposed to elevated diastolic pressure. But in 2019, an eight-year-long study involving more than 1.3 million adults found that while elevated systolic pressure had a greater effect on cardiac outcomes, high diastolic readings also affected a person's risk, regardless of the systolic reading.

To ensure accurate readings when you're checking your blood pressure at home, be sure to sit comfortably with your back supported, your feet flat on the floor, and your arm resting on a table with your palm facing up. If needed, support your arm with a pillow so that your elbow is at the level of your heart.

— Deepak L. Bhatt, M.D., M.P.H.
Editor in Chief, Harvard Heart Letter

Image: © Vadim Zhakupov/Getty Images

• April 2, 2010

Lowering Elevated Diastolic Blood Pressure Will Lessen Chance of Developing Elevated Systolic Blood Pressure

April 2, 2010

Dear Mayo Clinic:

I have normal systolic blood pressure, but my diastolic goes between 82 and 96 during the work day and goes down to normal at night or when there is no stress. Should I be concerned or is this normal?

Answer:

If you don't have other health issues that increase your risk of cardiovascular problems, the situation you describe — isolated diastolic hypertension — isn't dangerous now. But it's not normal, either. People with elevated diastolic blood pressure often develop elevated systolic blood pressure over time. You can help prevent that by taking steps to lower your diastolic blood pressure to a normal level.

A blood pressure reading, given in millimeters of mercury (mm Hg), has two numbers. The first, or upper, number measures the pressure in the arteries when the heart beats (systolic pressure). The second, or lower, number measures the pressure in the arteries between beats (diastolic pressure). Normal blood pressure is below 120/80 mm Hg.

Research regarding diastolic blood pressure has evolved considerably over the last several decades. During the 1970s and 1980s, many researchers and physicians believed the diastolic reading was the more important of the two blood pressure measurements. Now, we know they are both equally important.

Minimal elevations of diastolic blood pressure (less than 95 mm Hg) alone don't pose an immediate significant health risk. But that's assuming you're in good health otherwise and don't have any additional factors that put you at risk for cardiovascular problems. Those factors include diabetes, kidney disease, obesity, smoking, hardening of the arteries (atherosclerosis), or a history of heart disease or a heart attack.

If you don't have any additional risk factors, regularly monitoring your blood pressure and making lifestyle changes to decrease your diastolic blood pressure may be all that's necessary at this time. Taking steps to reduce your blood pressure to a normal level is important because an elevated diastolic pressure puts you at a higher-than-average risk of developing elevated systolic blood pressure as you age. Changes that can make a difference include eating a low-salt diet, avoiding alcohol, exercising regularly, not smoking and maintaining a healthy weight.

If you have other cardiovascular risk factors, any elevation in diastolic blood pressure — even if it's small — significantly increases your risk of cardiovascular problems. If that's the case for you, I strongly recommend you work with your physician to create a comprehensive treatment plan that addresses all your risk factors, including high blood pressure.

Effective management of high blood pressure is important because if left untreated it can have serious, long-term consequences. High blood pressure damages the lining of the blood vessels and accelerates hardening of the arteries throughout the body. This, in turn, can lead to a variety of health issues, such as cerebrovascular disease, heart attack and peripheral vascular disease, among others. These are cholesterol-related complications that people often think of when considering health problems associated with high blood pressure.

But there's another way high blood pressure is equally dangerous. The constant pounding of high blood pressure on blood vessels can also lead to serious health problems, including the type of stroke where there is bleeding in the area between the brain and the tissues that cover it (subarachnoid hemorrhage), congestive heart failure, kidney failure and abdominal aortic aneurysm.

In addition, increasing evidence suggests a correlation between high blood pressure and dementia. Research has shown that successful treatment of high blood pressure is associated with a reduced risk for dementia and Alzheimer's disease. So, to protect the brain, treat high blood pressure.

To effectively address your situation, I encourage you to make an appointment with your doctor to assess your elevated diastolic blood pressure and, based on your health history and other medical issues, develop a plan to manage it appropriately.

—John Graves, M.D., Nephrology and Hypertension, Mayo Clinic, Rochester, Minn.

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