The study analyzed data from a cohort of 1,457 participants (mean age, 58 years) who did not have any traditional cardiovascular risk factors and had a systolic blood pressure level between 90 and 129 mm Hg at baseline. Results showed that, during a mean follow-up of 14.5 years, there was an increase in traditional cardiovascular risk factors, coronary artery calcium, and incident cardiovascular events with increasing systolic blood pressure levels.
“We modeled systolic blood pressure on a continuous scale and saw the risk increasing in a linear fashion as blood pressure increased and this occurred right down to 90 mm Hg. We didn’t see any nadir or J-point where there may be an increased risk at lower pressures,” said lead author Seamus Whelton, MD.
Dr. Whelton is assistant professor of medicine at the division of cardiology at Johns Hopkins Medicine, Baltimore. He is the son of Paul Whelton, MD, chair of the 2017 American College of Cardiology/American Heart Association hypertension guideline writing committee.
“From an individual level we can now say that in healthy individuals, a systolic pressure in the 90s is not too low. It is a positive thing. And it is recommended to try and keep systolic pressure at these levels if possible by maintaining a healthy lifestyle,” Dr. Whelton said in an interview. “At a population level this finding could lead to stronger recommendations on interventions to prevent increasing blood pressure such as healthier diets, reducing sodium intake, and increasing exercise. Small changes in blood pressure on a population level will lead to large changes in cardiovascular risk on a population a level.”
The study was published online in JAMA Cardiology on June 10.
The researchers noted that populations in nonindustrialized countries have little to no increase in systolic blood pressure levels with age, while systolic blood pressure levels typically increase with age in countries with industrialized diets and lifestyles. This has important implications, because atherosclerosis is a slowly progressive disease and the lower an individual’s lifetime exposure to cardiovascular risk factors, such as increased systolic blood pressure, the lower their probable risk for a future cardiovascular event, they wrote.
While the association between systolic blood pressure level, coronary artery calcium, and atherosclerotic cardiovascular disease is well established at higher blood pressure levels, optimal systolic pressure levels for a healthy adult and whether there is a J-shaped relationship or lower limit of systolic pressure necessary to maintain adequate organ perfusion has been uncertain, they explained.
In addition, prior studies have typically used a reference systolic pressure of less than 115-120 mm Hg to define a normal level, and it is uncertain whether there is a lower level at which the risk for incident cardiovascular disease plateaus or increases.
To investigate this, they analyzed data from the Multi-Ethnic Study of Atherosclerosis, a community-based, multiethnic cohort free from known cardiovascular disease at enrollment. The current analysis included individuals with a systolic blood pressure between 90 and 129 mm Hg without other traditional cardiovascular risk factors including dyslipidemia (LDL cholesterol >160 mg/dL or HDL cholesterol <40 mg/dL), diabetes, or current tobacco use.
Results showed an adjusted hazard ratio for atherosclerotic cardiovascular disease was 1.53 for every 10 mm Hg increase in systolic blood pressure levels.
Compared with people with systolic pressures of 90-99 mm Hg, the adjusted hazard ratio for atherosclerotic cardiovascular disease risk was 3.00 for those with 100-109 mm Hg, 3.10 for those with 110-119 mm Hg, and 4.58 for those with 120-129 mm Hg.
There was also a graded increase in the prevalence of coronary artery calcium starting from systolic blood pressure levels as low as 90 mm Hg.
“Previous research on the J-shaped curve for blood pressure has primarily focused on diastolic pressure. We did control for diastolic pressure in this analysis but that was not the focus,” Dr. Whelton said. “Obviously, there will be a minimum optimum value for both diastolic and systolic pressure. But from this study we can say that for systolic pressure, that minimum recommended value is below 90 mm Hg.”
In terms of implications, the researchers wrote: “Among individuals at low or intermediate atherosclerotic cardiovascular risk, it may be more efficacious to focus on a life-course approach for preventing an increase in systolic blood pressure levels rather than treatment of established hypertension to lower systolic blood pressure levels.”