People who had high blood pressure (BP) while lying flat on their backs had an increased risk of heart attack, stroke, heart failure or premature death, according to new research.
The study defines high BP as having top and bottom blood pressure measures greater than or equal to 130/80 mm Hg.
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 properly regulate blood pressure during lying, seated and standing positions, said the researchers from Harvard Medical School in Boston.
People who had high BP while seated and supine had a 1.6 times higher risk of developing coronary heart disease; a 1.83 times higher risk of developing heart failure; a 1.86 times higher risk of stroke; a 1.43 times higher risk of overall premature death; and a 2.18 times higher risk of dying from coronary heart disease.
Participants who had high BP while supine but not while seated had similar elevated risks as participants who had high blood pressure while both seated and supine.
Differences in blood pressure medication use did not affect these elevated risks in either group, the team said.
"If blood pressure is only measured while people are seated upright, cardiovascular disease risk may be missed if not measured also while they are lying supine on their backs," said lead study author Duc M. Giao, a researcher at Harvard Medical School.
"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 added.
To examine body position, blood pressure, and heart health risk, the researchers examined health data for 11,369 adults.
Participants had their blood pressure taken while briefly lying down at a clinic and were followed for an average of 25 to 28 years. The findings showed that 16 per cent of participants who did not have high BP while seated had high BP while lying supine (flat on their backs).
"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," Giao said.
The study’s limitations included that it focused on adults who were middle-aged at the time of enrollment, meaning the results might not be as generalisable to older populations, Giao noted.
The findings will be presented at the American Heart Association’s Hypertension Scientific Sessions 2023, to be held from September 7-10 in Boston.