Older adults with sustained high blood pressure from middle age to late life showed more signs of brain disease, specifically brain lesions. In addition, elevated blood pressure readings were associated with tau tangles, a hallmark of Alzheimer's disease. These are results of an observational study published online in the July 11 issue of Neurology.
A team of researchers from the Rush Alzheimer's Disease Center at Rush University Medical Center in Chicago, followed 1,288 men and women, aged 59 to 102 years, until they died, on average eight years, and up to 24 years after enrolling in the study.
The researchers collected blood pressure data at baseline and annually and noted the participants’ use of medications, including antihypertensives. Healthy blood pressure is defined as less than 120/80 millimeters of mercury (mmHg); anything above 140/90 mmHg is considered high blood pressure. The first number, known as systolic blood pressure, measures the pressure in the blood vessels when the heart beats; the second number, diastolic, measures the pressure in the blood when the heart is at rest.
On average, participants had a blood pressure of 134/71 mmHg. Two-thirds of participants had a history of high blood pressure and 87 percent were taking blood pressure medication.
A higher average systolic blood pressure over the years led to an increased risk of brain lesions—areas of dead tissue caused by a blockage of the blood supply. Lesions, also known as infarcts, are more common with age and can lead to stroke.
Individuals with one standard deviation above the average systolic blood pressure—147 mmHg to 134 mmHg—had a 46 percent increased risk of developing one or more brain lesions. These individuals also had a 46 percent likelihood of having large lesions and a 36 percent risk of very small lesions. Researchers also looked for brain lesions
A more surprising finding was that declining systolic blood pressure over the years also put individuals at a higher risk for brain lesions. “The association of decline in SBP with infarcts is a novel and important finding," the researchers, led by Zoe Arvanitakis, MD, MS, who specializes in neurology at Rush University Medical Center in Chicago, wrote.
Typically, declining systolic blood pressure has been observed in the very old, and reported to be associated with mortality.
The researchers also found higher than average diastolic blood pressure was linked to brain lesions. An increase of one standard deviation from an average diastolic blood pressure, 71 mmHg to 79 mmHg, led to a 28 percent greater likelihood of one or more brain lesions. The results remained true even after researchers controlled for other factors that could affect the risk of brain lesions, such as whether they used high blood pressure drugs.
At the start of the study, participants signed an informed consent document and were asked to donate their brains upon death. Researchers analyzed the donated brains to look for common signs of aging as well as the distinctive plaques and tangles of Alzheimer's disease.
The autopsies revealed a link between higher systolic blood pressure in the years leading up to a participant's death and the number of brain tangles. In late life, as systolic blood escalated, so did the number of tangles in the brain. However, high blood pressure readings did not predict an increased presence of plaques in postmortem brains.
It remains unclear why a difference exists between these two hallmarks of Alzheimer's and blood pressure. Further research is necessary to interpret this finding, the investigators concluded.
The observational study does not prove higher blood pressure causes Alzheimer's disease. It only demonstrates the link between elevated blood pressure in late-life and the existence of tangles and plaques.
"While our findings may eventually have important public health implications for blood pressure recommendations for older people, further studies will be needed to confirm and expand on our findings before any such recommendations can be made," Dr. Arvanitakis said.
Read more about the dangers of high blood pressure in Control Your Blood Pressure, Save Your Brain. For ways to keep your blood pressure in check, read 6 Questions About Blood Pressure.