En español | You're probably aware that high blood pressure can increase your risk of developing heart disease and stroke. Researchers are now zeroing in on how it also ups your chances of getting dementia and its common predecessor, mild cognitive impairment (MCI). While these links have been recognized for a while, few long-term studies have examined the relationship between hypertension at midlife or later with the subsequent risks of cognitive decline and dementia — until now.
In a study published this month in JAMA, researchers tracked the blood pressure patterns of more than 4,700 people for 24 years, from mid- to late life, to see if they were associated with dementia risk. It turns out that those who had hypertension at midlife (ages 44 to 66) and later in life (ages 66 to 90) had a 49 percent increased risk of developing dementia, compared to those whose blood pressure stayed in the normal range.
Experts say that's a sizable increase coming from one specific, and easily measured, factor. “These data suggest that controlling blood pressure throughout life has a greater impact on lowering dementia risk than such risk-reduction behaviors as engaging in regular physical exercise or consuming a healthy diet,” says Gary Small, M.D., director of the UCLA Longevity Center.
But researchers saw an even bigger risk for both dementia and MCI in people who had high blood pressure in midlife, followed by low blood pressure at later ages.
Specifically, those who had hypertension (defined as a reading of 140/90 or higher) at midlife, followed by hypotension (90/60 or lower) later in life, had a 65 percent increased risk of developing MCI and a 62 percent higher risk of developing dementia.
Behind the numbers
It has long been recognized that chronic hypertension is harmful to blood vessels in the brain, which can in turn compromise the delivery of blood. “The brain is very responsive to lack of blood flow or to too much blood flow,” notes study lead author Keenan Walker, an assistant professor of neurology at the Johns Hopkins University School of Medicine in Baltimore.
The reason hypertension at midlife is so deleterious to the brain later on is likely related to the cumulative damage it causes to smaller blood vessels and capillaries, decade after decade. “[Damaged] blood vessels can't dilate and constrict in response to changes in blood pressure,” Walker explains. “And that can cause ischemic damage like ministrokes and arteriosclerosis that prevents blood from delivering oxygen and nutrients to the brain the way it's supposed to.”
All of these changes can lead to difficulties with various cognitive functions, including memory, processing speed, executive function and language skill.
It's also bad for the brain when people with previously high blood pressure at midlife develop low blood pressure later on, which can happen particularly when hypertension is overtreated with medication. When this occurs, “the blood vessels in the brain become less responsive to changes in blood pressure, and the brain can't compensate for that loss in blood flow the way it used to,” Walker explains.
What you can do
"Monitor your blood pressure and take it seriously throughout life, and try to keep it in the normal range, whether it's through medications or lifestyle modifications,” Small advises. (For the record, normal blood pressure is now defined as less than 120/80.)
If you end up taking medication to reduce hypertension, monitor your blood pressure closely to make sure it stays in the normal range. “As you get older, you don't want your blood pressure to get too high or to drop down into the hypotension range,” Walker says. “Overtreatment of hypertension can be just as harmful as undertreatment” when it comes to the health and functioning of your brain.