Stroke risk is greater with both higher and lower than normal blood pressure

Summary: lower than normal blood pressure results from underlying causes that need investigation and treatment. These underlying factors can increase the risk of stroke comparable to higher than normal blood pressure.An important study recently published in the JAMA (The Journal of the American Medical Association) offers evidence that lower than normal blood pressure is a risk factor for stroke comparable to blood pressure that is higher than normal. The authors state:

"Recurrent stroke prevention guidelines suggest that larger reductions in systolic blood pressure (SBP) are positively associated with a greater reduction in the risk of recurrent stroke and define an SBP level of less than 120 mm Hg as normal. However, the association of SBP maintained at such levels with risk of vascular events after a recent ischemic stroke is unclear."

So they set out to...

"...assess the association of maintaining low-normal vs high-normal SBP levels with risk of recurrent stroke."

They examined two and a half years of data for 20,330 patients from 35 countries who had recently had an ischemic stroke. Patients were categorized based on their average systolic blood pressure as very low–normal (<120 mm Hg), low-normal (120-<130 mm Hg), high-normal (130-<140 mm Hg), high (140-<150 mm Hg), and very high (≥150 mm Hg). Their primary outcome measure was a stroke of any kind, and the secondary outcome was a composite of stroke, heart attack, or death from any other vascular cause. What did the data show?

"The recurrent stroke rates were 8.0% for the very low–normal SBP level group, 7.2% for the low-normal SBP group, 6.8% for the high-normal SBP group, 8.7% for the high SBP group, and 14.1% for the very high SBP group. Compared with patients in the high-normal SBP group, the risk of the primary outcome was higher for patients in the very low–normal SBP group (adjusted hazard ratio [AHR], 1.29), in the high SBP group (AHR, 1.23), and in the very high SBP group (AHR, 2.08). Compared with patients in the high-normal SBP group, the risk of secondary outcome was higher for patients in the very low–normal SBP group (AHR, 1.31), in the low-normal SBP group (AHR, 1.16), in the high SBP group (AHR, 1.24), and in the very high SBP group (AHR, 1.94)."

In other words, while the very high systolic blood pressure was the worst for both primary and secondary outcomes, the very low-normal group was the 'runner up' for both recurrent stroke  (29%) and the secondary outcomes of heart attack or death from other vascular causes (31%). The authors conclude:

"Among patients with recent non–cardioembolic ischemic stroke, SBP levels during follow-up in the very low–normal (<120 mm Hg), high (140-<150 mm Hg), or very high (≥150 mm Hg) range were associated with increased risk of recurrent stroke."

It's important for both clinicians and patients to understand that lower than normal blood pressure is an indicator that things 'under the surface' are not working as they should. For example, autoimmune disorders that are Th1 dominant can be associated with lower adrenocortical activity due to the effect on the brain's paraventricular nucleus—while promoting vascular inflammation.