But in a study published in the journal Neurology, researchers led by Dr. Zoe Arvanitakis, medical director of the Rush Memory Clinic at Rush Alzheimer’s Disease Center, find more evidence that blood pressure may be one of those risk factors.
Previous studies have implicated high blood pressure as a possible risk factor for dementia, including Alzheimer’s dementia, but there are few studies exploring how blood pressure, particularly among older people, affects tissues in the brain. In the study, Arvanitakis and her colleagues measured the blood pressure of nearly 1,300 elderly people, aged 59 to 102 years, and followed them until they died, on average eight years after enrolling in the study. The scientists performed autopsies on the brains to document the presence of brain lesions, including signs of Alzheimer’s disease, which is characterized by the presence of protein plaques known as amyloid, and tangles of dying and dead nerve fibrils known as tau.
The American Heart Association says that blood pressure should ideally be 120/80 mmHg or below. During the study, the average blood pressure was about 134/71 mmHg, which is considered pre-hypertensive. People with higher blood pressure across the study period tended to have more brain lesions, known as infarcts, which are areas of dead brain tissue that have lost their blood supply. Infarcts can lead to strokes, but many go undetected. People with higher blood pressure also showed more tau tangles, although they did not show significant differences in the other Alzheimer’s feature, amyloid plaques. In fact, an increase in systolic pressure (the top blood pressure number) from 134 mmHg to 147 mmHg was linked to a 46% higher chance of having one or more brain infarcts.
“We think that it’s potentially biologically plausible that altered blood pressure later in life can cause infarcts [in the brain], given the body of literature in which we know that blood pressure is associated with stroke,” says Arvanitakis. She says the study does not show that high blood pressure actually causes brain lesions, and further research is needed to explore that connection.
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The study provides more evidence that blood pressure may be one of the many factors that can contribute to aging brain processes, including the formation of lesions and hallmark features of diseases like Alzheimer’s. Arvanitakis says she and her team plan to continue analyzing data from the participants to better understand how blood pressure affects the brain—including, for example, whether those who lowered their blood pressure during the study were able to reduce the formation of infarcts. (Interestingly, people with extreme drops in blood pressure during the study also had a higher risk of more infarcts, likely because the decline represented other serious health issues.)
Most of the people in the study were taking medications to keep their blood pressure under control, but she notes that higher readings, even if they weren’t excessively high, were associated with more brain lesions. “We are not talking here about people with very high blood pressure,” she says. “We’re talking about pretty average blood pressure and what blood pressure across the whole range of readings can do to the brain.”
Until more research is done, Arvanitakis says the results should encourage people to focus on maintaining healthy blood pressure not just for their heart, but for brain health, as well. “Many, many issues are important for brain health and for avoiding brain diseases,” she says, “so we should consider them all in order to be as healthy as possible as we grow into the later stage of life.”