High Blood Pressure Linked to Sign of Alzheimer's Disease: Study

Scientists have found a link between high blood pressure and tangles in the brain seen in those with Alzheimer’s disease.  Getty Images

Scientists have found a link between high blood pressure and tangles in the brain seen in those with Alzheimer's disease.

Characterized by blood pushing against the walls of the arteries at too high a force for a prolonged period of time, high blood pressure is a common condition. Around 75 million, or one in three, adults in the U.S. have high blood pressure—or hypertension—according to the Centers for Disease Control and Prevention.

To investigate the relationship between high blood pressure and brain health, researchers studied 1,288 participants until they died. On average, each individual was studied for eight years and died at 89 years of age.

The team measured their blood pressure annually. When the participants died, an autopsy was performed on their brains with their consent to check for signs of brain aging, such as tangles and levels of amyloid beta plaque believed to play a role in the development of Alzheimer's. They also looked for brain lesions called infarcts, which are made of dead tissue caused by low blood supply, something that can become more common as we age. Infarcts can cause strokes.

When scientists and clinicians assess blood pressure, they use two measures. Systolic blood pressure in the blood vessels when the heart is contracting—which should be 120mmHg or less—and diastolic blood pressure, or between beats, which should measure 80mmHg or less. (The abbreviation mmHg refers to "millimeters of mercury," or the height a column of mercury rises when reading blood pressure.)

On average, the participants had a blood pressure of 134/72mmHg, or 134 systolic over 72 diastolic. Two thirds of the individuals had a history of high blood pressure, with 87 percent taking medication.

The autopsies revealed an association between a higher than average systolic blood pressure in the years leading up to an individual's death, and the number of brain tangles. Scientists didn't, however, find the same link with plaque.

The data indicated the higher a person's systolic blood pressure, the higher their risk of developing brain lesions. One standard deviation above average systolic blood pressure, for instance 147 mmHg versus 134 mmHg, carried a 46 percent increased risk of having at least one brain lesions, particularly infarcts. A total of 48 percent of participants had at least one brain infarct lesion.

The effect of this was the equivalent of nine years of brain aging, the researchers said. But the researchers also found a declining systolic blood pressure carried a risk of developing one or more brain lesions.

When diastolic blood pressure was assessed, researchers found individuals with an increase of one standard deviation from the average—for instance from 71mmHg to 79mmHg—carried a 28 percent higher risk of having one or more brain lesions.

The conclusion remained the same even when factors such as the use of blood pressure medication were taken into account, the study authors noted. The results were published in the journal Neurology.

Dr. Zoe Arvanitakis, author of the study based at the Rush Alzheimer's Disease Center at Rush University Medical Center in Chicago, commented in a statement: "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. Doug Brown, chief policy and research officer at the U.K.-based charity the Alzheimer's Society, told Newsweek that having high blood pressure in middle age is "known to increase dementia risk in later life, particularly vascular dementia."

"While this study linked raised blood pressure later in life to early changes in the brain associated with Alzheimer's disease—a build-up of tangles—it was an observational study and we don't know if the people studied had a diagnosis of Alzheimer's disease so we cannot draw firm conclusions."

As the number of people being diagnosed with Alzheimer's grows, he said, "we need to look at all ways we can reduce the chance of getting dementia.

"The next step could be to explore the effects of controlling blood pressure at a healthy level during mid and late life to see whether this can reduce the risk of developing Alzheimer's."

This article was updated to provide background information.