What causes high blood pressure when you are lying down?

Blood pressure³ refers to the pressure exerted on the walls of the arteries as your heart pumps blood. Blood pressure measurements are taken in two numbers, measured in millimeters of mercury (mm Hg).

The top/first number is the systolic blood pressure, and it indicates how much pressure is being exerted on the artery walls when your heart pumps blood. It is the highest of the two numbers, and an increase above normal is a cause for alarm. The bottom/second number is the diastolic blood pressure, and it is the measurement of the pressure being exerted by your blood on the artery walls when your heart is resting between beats.

120/80 mm Hg is considered the normal blood pressure reading for an adult. An increase in either the systolic or diastolic blood pressure can indicate hypertension. There are different blood pressure categories depending on how high either of the measurements is.

They include:

Elevated blood pressure

Elevated blood pressure occurs when your systolic blood pressure ranges from 120-129 mm Hg, with the diastolic blood pressure less than 80mm Hg. Individuals with elevated blood pressure are on the road to high blood pressure unless they take immediate action to control and reduce their blood pressure.

Stage 1 hypertension

Stage 1 hypertension is also known as prehypertension, and it occurs when the systolic blood pressure is about 130-139 mm Hg and the diastolic blood pressure around 80-89 mm Hg. If you have stage 1 hypertension, the doctor is likely to recommend lifestyle changes to help control hypertension before it advances.

Supine hypertension is present in about half of people with autonomic failure, a chronic degenerative disease that affects the part of the nervous system that regulates involuntary functions such as blood pressure and heart rate. Overnight increases in blood pressure are associated with damage to the heart and kidneys.

Since then, healthcare providers continue to find new ways to glean information about your health from your blood pressure readings. Here’s a rundown of what your blood pressure readings can mean for your heart health.

Before we dive in, let’s first take a look at what blood pressure means in our body. Blood pressure is the pressure generated with each heartbeat, says Jennifer Wong, MD, cardiologist and medical director of noninvasive cardiology at MemorialCare Heart and Vascular Institute at Orange Coast Medical Center in Fountain Valley, California.

Blood pressure is given in two numbers, with acceptable ranges for each one. The top, or systolic number, is the pressure inside your arteries when your heart “squeezes or contracts,” explains Dr. Wong, while the bottom, or diastolic number, “is when the heart is relaxed.” You want those numbers to be below 120 and 80, respectively.

Blood needs to flow at a certain pressure to supply blood to our organs and body. But blood pressure that’s too high can cause damage to your circulatory system.

When left untreated, high blood pressure increases your risk of a heart attack, organ damage and failure, as well as contribute to stroke and peripheral vascular disease, per Hopkins Medicine.

Currently, almost 1 out of 2 (about 116 million) adults in the United States have high blood pressure, and 92.1 million don’t have their high blood pressure under control, according to the Million Hearts, a national initiative co-led by the Centers for Disease Control and Prevention (CDC) and the Centers for Medicare and Medicaid Services.

Wong says high blood pressure can also be more prevalent with age. "We check for blood pressure at nearly all ages, but we start seeing an upward trend as we get older, over age 40. So you need to pay closer attention to what's happening with your blood pressure around that age and start treating it if necessary.” According to Mayo Clinic, people over 40 should have their blood pressure checked every year.

High blood pressure plays a significant role in pregnancy, too. It can spell trouble for mom and baby if it’s not monitored or controlled. High blood pressure can affect a mother’s kidneys and increase her risk of heart disease and stroke, and can cause complications such as preeclampsia, per the American College of Obstetricians and Gynecologists, as well as low birth weight and preterm delivery. If you have high blood pressure before you get pregnant, you're more likely to have certain complications during pregnancy than women who have normal blood pressure.

High blood pressure among pregnant women has doubled in the United States between 2007 and 2019, according to a study published in May 2022 in the Journal of the American Heart Association. That’s why monitoring your blood pressure is a vital part of prenatal care.

In a study published in April 2022 in The New England Journal of Medicine, researchers found that pregnant women with mild hypertension who were given antihypertensive medications experienced fewer birth complications. For the open-label, randomized trial, scientists studied 2,408 pregnant women with hypertension by placing them in active treatment and control groups. Women assigned antihypertensive medications were in the active treatment group, while those in the control group did not get any such medicines unless their hypertension became severe.

The researchers found that the active treatment group had fewer maternal and birth complications than the control group, concluding it's best to target blood pressure levels of less than 140/90 mm Hg to promote better pregnancy outcomes.

For people who have low blood pressure, it may be a sign that organs aren't getting enough blood.

"Most people don't show severe symptoms until their blood pressure hits very low levels, like a systolic blood pressure less than 80 mm Hg and a diastolic blood pressure less than 40 mm Hg," says Wong. Chronic illnesses such as severe inflammation or sepsis can cause dangerously low blood pressure levels, leading to heart failure. It's tough to determine how many people low blood pressure affects because there’s usually no symptoms. According to Mayo Clinic, conditions associated with low blood pressure include:

One type of low blood pressure that could predict future heart problems like bradycardia — as detailed by the American Heart Association — is postural or orthostatic hypotension. Here, a sudden drop in blood pressure happens when standing after sitting or lying down, causing dizziness, nausea, or even fainting. An estimated 5 percent of people at age 50 have it, and by age 70, more than 30 percent, research shows.

Orthostatic hypotension is also more prevalent in new moms, teenagers, and people who have been on bed rest, according to the National Organization for Rare Disorders.

Some research has found orthostatic hypotension to be associated with people who have heart failure. A study published in 2020 in the European Journal of Heart Failure found 10 to 15 percent of patients with heart failure were more likely to have low blood pressure, and in elderly patients, more than 10 percent had orthostatic hypotension.

About 1 in 3 adults in the United States with high blood pressure aren’t even aware they have it, according to the CDC.

Wong advises routine blood pressure checks at home and in your doctor's office to encourage early detection of illnesses and medical intervention.

Blood pressure readings to look out for, according to the American Heart Association:

“Our goal is to control blood pressure early on, especially at younger ages, when we're healthy and not feeling the negative effects of blood pressure yet, so we can maintain that health into our older ages,” says Wong.

Additional Resources:

NOTE: Actual presentation time is 4:30 p.m. CT/5:30 p.m. ET.

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