More than a billion adults around the world live with elevated blood pressure, a condition that puts individuals at risk of damaging a variety of organs, including the nervous system.
Though previous studies have linked high blood pressure (hypertension) with an increased risk of cognitive impairment, the mechanisms behind the decline in mental health has never been known.
Now an international team of researchers has discovered which areas of the brain are most likely to suffer damage as the cardiovascular system is put under strain.
"Our study has, for the first time, identified specific places in the brain that are potentially causally associated with high blood pressure and cognitive impairment," says Jagiellonian University Medical College medical biologist Mateusz Siedlinski.
Siedlinski and colleagues used a combination of genetic and imaging data and observational analyses from 33,000 individual records in the UK Biobank to find the damage caused by high blood pressure that contributes to dementia.
This combined approach allowed the researchers to identify where in the brain long-term hypertension can cause the structural changes that lead to declines in cognitive function, and what those changes look like in brain scan images.
"We thought these areas might be where high blood pressure affects cognitive function, such as memory loss, thinking skills, and dementia," explains cardiovascular physician Tomasz Guzik.
"When we checked our findings by studying a group of patients in Italy who had high blood pressure, we found that the parts of the brain we had identified were indeed affected."
Previous studies had suggested associations between total white brain matter and dementia, but not cognitive function. The improved detail provided by this new study's method showed some regions of white matter play a greater role than others in determining cognitive health, making broad measurements of the tissue an unreliable indicator for neurological impairment.
Focusing in on specific parts of the white matter, Siedlinski and team found changes in nine distinct areas related to both high blood pressure and worsening brain function.
One section located at the base of the forebrain, called the putamen, is essential to our responses to stimuli and learning. Other regions identified are involved in executive function, decision-making, and emotional regulation, as well as white matter tracts that act as communications channels between different brain regions.
What's more, the team found structural changes were primarily a consequence of a difference between systolic pressure – the pressure in arteries when your heart beats – and diastolic pressure – the pressure in between beats. Higher systolic blood pressure and pulse pressure (systolic blood pressure minus diastolic blood pressure) impacted cognitive decline, whereas higher diastolic blood pressure seemed to have a protective effect when systolic pressure is taken into account.
This could explain mixed results seen in previous studies that examined potential links between blood pressure and cognitive decline.
The UK biobank mostly contains data from white, middle-aged people, so more research is required to confirm these findings remain true across diverse demographics. Nonetheless, the results provide researchers with promising directions to continue investigations.
"We hope that our findings may help us to develop new ways to treat cognitive impairment in people with high blood pressure," says Guzik. "Studying the genes and proteins in these brain structures could help us understand how high blood pressure affects the brain and causes cognitive problems.
"Moreover, by looking at these specific regions of the brain, we may be able to predict who will develop memory loss and dementia faster in the context of high blood pressure," Guzik continues.
"This could help with precision medicine, so that we can target more intensive therapies to prevent the development of cognitive impairment in patients most at risk."
This research was published in the European Heart Journal.