U-M study: Even slightly elevated systolic blood pressure pushes up stroke risk by 20%

If your systolic blood pressure — the top number of your blood pressure reading — consistently edges above normal, new research from the University of Michigan suggests you're at an increased risk for stroke.

A study published in JAMA Open Network found that if a person's systolic blood pressure hovers 10 points above the 120 mmHg threshold over a sustained period of time, that person's risk for ischemic stroke is 20% higher and the chances of an intracerebral hemorrhage climbs by 31%.

"We focused on systolic blood pressure because it is the strongest predictor of cardiovascular outcomes, particularly stroke but also heart attack," said Dr. Deborah Levine, a professor of medicine at the University of Michigan Medical School, a senior author of the study, which analyzed data from more than 38,000 U.S. adults over an average span of 21 years.

"We combined six studies that have followed participants over many years, and enrolled participants at different ages to examine how high blood pressure over the life-course influences stroke risk."

Stroke is the fifth-leading cause of death in Michigan, and killed 5,775 people in 2022 alone, according to the Michigan Department of Health and Human Services. More than a third of Michigan adults have high blood pressure.

"High blood pressure is underdiagnosed and undertreated and undercontrolled," Levine said. "And yet, it's the most important stroke risk factor."

The research, Levine said, highlights the importance of identifying high blood pressure early and taking steps to lower it, such as adopting better eating and exercise habits and adding antihypertensive medication when lifestyle changes alone aren't enough.

"Health care providers need to intensify blood pressure treatment, to control blood pressure to goal levels in all adults," she said.

Racial disparities in stroke prevalence

The study examined data from a diverse group of patients: 54% were women; 25% were Black; 8.9% identified as Hispanic, and 66.2% identified as white.

Researchers found no racial or ethnic differences in the stroke risk associated with long-term elevated systolic blood pressure — even though Black and Hispanic Americans are disproportionately affected by strokes.

"We saw no evidence that high cumulative systolic blood pressure had a greater effect on stroke risk in Black or Hispanic adults compared to white adults," Levine said. "So this suggests that ... higher blood pressure in these minority groups is likely due to worse access to care, and treatment and control of blood pressure."

Controlling blood pressure makes a difference

"Adults should be monitoring their blood pressure at home periodically to ensure that their blood pressure is at goal level. Seeing your health care provider once a year is just one snapshot in time. Along with that, my group has shown how home monitoring improves the diagnosis and control of blood pressure and is an underused but highly effective and cost-effective strategy."

Because blood pressure readings can be influenced by outside factors such as stress, anxiety, caffeine and alcohol intake, Levine recommends all adults ages 30 and older take their blood pressure readings at home twice a day over the course of one week each month. An average of that week's readings will give a better sense of what their blood pressure actually is.

Taking the readings at home also can eliminate what's known as the "white coat effect," which occurs when a person's blood pressure rises when they're at a doctor's office because they might be nervous or anxious about the appointment.

At-home blood pressure monitors can be purchased for as little as $20-$25. Levine recommends purchasing a monitor that has been tested by the independent U.S. Blood Pressure Validated Device Listing website, www.validatebp.org , and found to provide accurate readings.

"Unfortunately, most insurance (companies) do not cover them," Levine said. While paying $20-$25 for an at-home monitor might not be out of reach for some people, others cannot afford the expense — exacerbating health inequities.

"Although self-monitoring of (blood pressure) improves (blood pressure) control and is cost-effective, it is an underused tool, and cost is a barrier, making patient education and greater insurance coverage priorities," the study authors wrote.

What is considered high blood pressure?

"High blood pressure is defined as blood pressure of 130/80 or higher on at least two occasions," Levine said.

The top number, a person's systolic blood pressure, measures the pressure against the walls of your arteries every time your heart beats. The diastolic pressure is the lower number on a reading, and measures the pressure against the artery walls when the heart is resting between beats.

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Up until 2017, the threshold for what should be classified as hypertension was set at 140/90 mmHg. But research published around that time led the American Heart Association, the American College of Cardiology and other health organizations to lower the definition of hyertension to 130/80 mmHg.

Under the newer guidelines, blood pressure levels should be calculated with an average of two to three readings over at least two separate occasions.

• Normal is considered less than 120/80 mmHg.
• Elevated blood pressure occurs when a person has a systolic pressure of 120-129 mmHg (top number) and a diastolic pressure (bottom number) that's lower than 80 mmHg.
• Stage 1 hypertension is classified as a systolic blood pressure between 130-139 mmHg or a diastolic blood pressure between 80-89 mmHg.
• Stage 2 hypertension occurs when the systolic pressure is at least 140 mmHg or diastolic pressure at least 90 mmHg.
• A hypertensive crisis is a medical emergency and occurs when the systolic pressure is over 180 mmHg and/or the diastolic pressure is over 120 mmHg.

Many people aren't aware of the now-lower thresholds for what should be classified as high blood pressure, Levine said. Others have heard inaccurate information about hypertension.

"When I see patients who had a recent stroke, it is so unfortunate how many had high blood pressure readings before the stroke that wasn't addressed," Levine said.

"Another myth is that older adults should be allowed to have a higher blood pressure — that they don't need to control it. But that's not accurate. We need to treat all adults the same, regardless of age."

Recipe for lower blood pressure

When it comes to hypertension, sometimes the best medicine, Levine said, is a lifestyle change.

Levine recommends:

• A low-salt diet, consuming less than 1,500 milligrams of salt a day.
• Exercise 30 minutes, five days a week.
• Weight loss for anyone who is overweight or obese based on body mass index .
• Avoid or limit alcohol intake.
• Talk with your doctor about whether you also need medication to control your blood pressure.

Contact Kristen Shamus: kshamus@freepress.com. Subscribe to the Free Press .

This article originally appeared on Detroit Free Press: U-M study: Even slightly elevated systolic blood pressure pushes up stroke risk by 20%