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More data suggest that hypertension could have a negative effect on cognitive function. Image credit: Asya Molochkova/Stocksy.
  • High blood pressure can increase the risk of heart disease and stroke, and it can also have a negative impact on brain health.
  • Over time, it can impair the brain’s ability to clear toxins and by-products of metabolism.
  • Impaired brain waste clearance may increase the risk of dementia.
  • A new study has found that intensive treatment to lower blood pressure may boost brain clearance pathways.

According to the World Health Organization (WHO), around 1.28 billion adults aged 30–79 years have hypertension, or high blood pressure, and 46% of people with hypertension are unaware that they have the condition.

Hypertension often causes no symptoms, but it can increase the risk of heart disease, stroke, kidney disease, and other serious health conditions.

Studies have also shown that hypertension may increase a person’s likelihood of developing dementia, and that lowering blood pressure can decrease that risk.

A new analysis of data from the SPRINT-MIND MRI substudy is being presented at the International Stroke Conference 2023 in Dallas, TX.

This preliminary research suggests that reducing high blood pressure to less than 120 millimeters of mercury (mmHg) systolic blood pressure — the force at which the heart pumps out blood — may remodel brain clearance pathways, potentially reducing dementia risk.

Dr. Sandra Narayanan, a board-certified vascular neurologist and neurointerventional surgeon at Pacific Stroke & Neurovascular Center at Pacific Neuroscience Institute in Santa Monica, CA, not involved in the study, told Medical News Today why reducing blood pressure might be beneficial.

“Moderate blood pressure control is associated with fewer white matter hyperintensities, which is in turn linked to lower risk of vascular dementia and improved cognitive function,” she explained.

“Keeping hypertension under control reduces the risk of end-organ damage, such as scarring, narrowing, or blockage of fragile cerebral arteries that can cause ischemic or hemorrhagic stroke over the long term,” she added.

The study investigated 658 people who had hypertension, but no diagnosis of type 1 or 2 diabetes, dementia, or stroke.

At the beginning of the study, all the participants, who had an average age of 67 years, and 60% of whom were women, had brain MRI scans. The scans were carried out at seven locations across the United States.

Some participants then underwent intensive treatment for hypertension, which aimed to reduce systolic blood pressure to 120mmHg. Others were on a standard treatment program with a systolic blood pressure goal of 140mmHg.

After an average of 3.9 years, 243 people in the intensive treatment group and 199 in the standard treatment group had repeat brain MRI scans. Researchers then analyzed these scans and compared them with the scans taken at the start of the study.

The researchers looked at changes in perivascular spaces in the participants’ brains.

“Perivascular spaces (PVS) are cerebrospinal fluid-filled spaces, also called Virchow-Robin spaces, located in the pial layer of the brain,” explained Dr. Narayanan.

“They surround arterioles and venules in the deep white matter and can become enlarged with aging, inflammation, demyelinating disorders, or neurodegenerative processes. PVS facilitate [the] elimination of water and metabolic waste from the brain,” she told us.

When enlarged and visible on MRI scans, perivascular spaces may be associated with certain forms of dementia.

“It’s an open question in the field if perivascular space enlargement is a hallmark of glymphatic dysfunction/diminished brain waste clearance, but the research is slowly pointing to yes,” Dr. Lauren Hablitz, assistant professor of Neurology in the Center for Translational Neuromedicine at the University of Rochester Medical Center, not involved in this study, told MNT.

Dilated perivascular spaces indicate impairment of normal brain fluid and waste clearance.

Dr. Hablitz added: “It could be that with enlarged perivascular spaces, the fluid doesn’t get driven into the brain as well to clear the ‘garbage’ out.”

In this study, the researchers controlled for age and sex of the participants, and for the study site where the scans were performed. At the start, perivascular space volumes were similar in participants in both groups.

After almost 4 years of treatment, people in the intensive treatment group had a significant decrease in perivascular spaces. The researchers saw no reduction in the regular treatment group.

“The power of this study was the before and after in the same patients, because now that we have an intervention and effect in humans we can bring it back to basic lab studies to find how it works and test directly if brain waste clearance is impacted,” Dr. Hablitz commented.

Previous studies have shown a link between hypertension, white matter hyperintensities, and reduced brain volume, both of which are linked to dementia. The SPRINT-MIND MRI has previously found that intensive blood pressure treatment may slow the accumulation of white matter hyperintensities.

This substudy of SPRINT-MIND has found that intensive treatment of hypertension can also reduce perivascular spaces. It is possible that intensively lowering systolic blood pressure may promote better clearance of toxins and by-products and therefore maintain brain health.

The authors point out that they cannot determine whether this change in perivascular spaces has any effect on cognitive ability.

Lead author Dr. Kyle Kern describes how the research will develop: “The next step is to determine how perivascular spaces relate to cognition and cognitive decline in the SPRINT-MIND trial. That trial included high-quality cognitive function assessments at multiple time points, and forthcoming investigations from the trial will describe how perivascular spaces may relate to the effect of intensive blood pressure control on cognitive decline.”

With the number of dementia cases predicted to rise to more than 150 million by 2050, any measures to decrease dementia risk are welcome. This study adds to evidence that lowering blood pressure may reduce risk, and proposes the mechanism by which it might do so.

“I don’t think the field has a firm grip on what blood pressure does to glymphatic flow/ brain waste clearance, but these spaces are so small and tightly regulated that it’d be hard to imagine there isn’t an effect. This study tries a more direct approach to answer it, by using an intervention directed at blood pressure to resolve potential enlargement, and it looks like it may have worked.”

– Dr. Lauren Hablitz

It is well known that reducing blood pressure has many health benefits. Perhaps keeping blood pressure well inside the healthy range might also reduce a person’s risk of developing dementia.