The results of a 30-year study by researchers working with the American Heart Association (AHA) found that doctors should be taking two blood pressure readings: one, when the patient is sitting up and the second when the patient is lying down. Sometimes people with apparent normal readings when seated upright may have elevated blood pressure when they are supine.

“If blood pressure is only measured when people are seated upright, cardiovascular disease risk may be missed,” said lead study author Duc M. Giao, a medical student at Harvard Medical School.

According to a news release by the AHA, the long-running study of more than 11,000 adults from diverse backgrounds in the U.S. found that people with high blood pressure readings while seated upright and lying down had a higher risk of heart disease, stroke, heart failure or premature death compared to adults without high blood pressure in both positions.

The new research was presented at the AHA’s Hypertension Scientific Session 2023 held from September 7-10. Researchers explained that the autonomic nervous system regulates blood pressure in different body positions. However, gravity may cause blood to pool when seated or upright, and the body is sometimes unable to regulate blood pressure during lying, seated, and standing positions.

Among the research findings:

•16% of participants who did not have high blood pressure (readings measuring more than 130/80 mm Hg) while seated had high blood pressure when lying down flat on their backs. In comparison, 74%, or about three in four, of those with seated high blood pressure also had supine elevated hypertension.

• Participants who had high blood pressure while seated and supine had a 1.6 times higher risk of developing coronary heart disease and a 1.83 times higher risk of overall premature death. They also had a 2.18 times higher risk of dying from coronary heart disease compared to the study subjects who did not have high blood pressure while seated or lying down.

• Interestingly, the adults who had high blood pressure measured when lying down but not when seated, had the same elevated risks as participants who had high blood pressure while both seated and lying down, said the AHA news release.

According to Study Finds, the first phase of the study began in 1987 and continued until 1989. A total of 15,972 adults living in the U.S. with diverse backgrounds had their blood pressure taken when lying down or sitting up. Over half (56%) were women, and 25% of the participants were Black. Blood pressure data was gathered in both rural and urban clinics. Their health was then followed for an average of 25 to 28 years, with the latest health statistics collected between 2011 and 2013.

“Our findings suggest people with known risk factors for heart disease and stroke may benefit from having their blood pressure checked while lying flat on their backs,” Giao said. “Efforts to manage blood pressure during daily life may help lower blood pressure while sleeping. Future research should compare supine blood pressure measurements in the clinic with overnight measurements.”

One of the limitations of this new study is that the average age of participants was 54. It is possible that the results could differ for older populations, says Study Finds.

According to the Centers for Disease Control and Prevention, having high blood pressure puts you at risk for heart disease and stroke. In 2021, hypertension was a primary or contributing cause of 691,095 deaths in the U.S. Nearly half of adults have hypertension, defined as having a systolic blood pressure greater than 130 mm Hg or a diastolic blood pressure greater than 80 mm Hg.