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For a healthy brain as we age, we need healthy blood pressure.
However, nearly half of American adults have hypertension, which is one of the most common - and preventable - risk factors for developing dementia decades later, research shows.
Hypertension, or chronically high blood pressure, is a double whammy for the brain - making it harder for oxygen and nutrients to get into the brain and more difficult for the brain to get rid of metabolic waste products. Abnormally high blood pressure can damage the small blood vessels in the brain, causing brain injury and atrophy, and driving neuroinflammation.
When people have hypertension, especially in midlife, "they start losing blood flow to the brain, they start having impacts on the vasculature in the brain," said Silvia Fossati, an associate professor of neural sciences and the interim director of the Alzheimer's Center at Temple University School of Medicine. "And this is parallel and additive with the Alzheimer's pathology."
Hypertension is a risk factor for all-cause dementia as well as Alzheimer's disease, the most common form of dementia. Compared with people with normal blood pressure, those with hypertension have at least 1.5 times as high a risk for cognitive impairment and dementia.
Crucially, high blood pressure is preventable and modifiable, experts said.
"If there's one thing you do today to help your cognitive outcomes when you're 80 or 90, it's to take care of your heart health," said Ana Daugherty, an associate professor of psychology who researches aging and dementia risk at Wayne State University's Institute of Gerontology. "And that's true of anybody. It's never too late to start."
• Why hypertension hurts the brain
The brain is small but needy; it constitutes just 2 percent of body weight but demands at least 15 percent of our heart's blood output.
The brain is "hungry for what's in the blood," Daugherty said. "Anything that's going to disrupt that process is going to have small and large cumulative effects over time."
Blood flow in the brain is not constant and instead ebbs and flows with each heartbeat. Much of brain tissue is more akin to "a flood region where very, very small vessels are delivering blood," Daugherty said.
Normally, our brain automatically regulates its blood pressure, to maintain blood flow regardless of whether we are lying down or standing up, Fossati said.
Hypertension, however, breaks down this autoregulation, meaning that the same blood pressure leads to lower blood flow to the brain and insufficient oxygen and nutrient delivery.
At the same time, hypertension "makes it harder for the brain to remove waste products, such as amyloid beta," a biological hallmark of Alzheimer's disease, Fossati said.
Instead, the amyloid beta accumulates around the brain's blood vessels, which in turn makes it harder and harder for the brain to get rid of it.
"It's kind of like a vicious cycle," Fossati said.
Over the course of years and decades, hypertension can also damage blood vessels and disrupt normal function of the blood-brain barrier, which serves to prevent pathogens and other unwanted guests from entering the brain and can lead to more inflammation in the brain, which in turn increases the risk of dementia. Hypertension is also associated with accelerated brain atrophy.
Hypertension affects the entire brain, but some regions are particularly susceptible.
The hippocampus, a brain structure key to memory and learning, is one such area that also atrophies faster in Alzheimer's disease.
Sections of the hippocampus are fed by small blood vessels, which may bend up to 90-degree angles in some people, Daugherty said.
Its vascular size and shape already make it difficult for the hippocampus to clear waste and receive the oxygen and nutrients it needs to help us learn and remember. Hypertension makes it even more difficult, which may be a reason the hippocampus is one of the first areas affected in Alzheimer's disease, researchers said.
• Hypertension increases the risk for dementia
In the 2024 Lancet Commission report on dementia, hypertension is one of 14 modifiable risk factors, many of which relate to heart health and which together account for 45 percent of dementia cases.
Longitudinal studies have reported that midlife hypertension is a predictor of a faster rate of cognitive decline involving memory, information processing and executive processing.
There are normal fluctuations in blood pressure throughout the day and in different conditions such as with stress, sleep or dehydration, Daugherty said.
A hypertension diagnosis would require persistent high blood pressure - greater than 130 mmHg systolic pressure (when your heart contracts) and greater than 80 mmHg diastolic pressure (when your heart is relaxed) - across multiple measurements.
Hypertension can be complicated and associated with related disease symptoms such as cardiovascular disease or stroke that also increase dementia risk.
But even in people who are otherwise healthy, having just hypertension increases the risk of accelerated brain aging, cognitive decline and dementia.
Managing hypertension with medication can mitigate dementia risk but does not eliminate it.
• How to manage hypertension and dementia risk
Researchers do not fully understand the direct causes of hypertension, Daugherty said. "Our current treatment strategies are all about symptom management." Because hypertension is a lifelong health condition, "the best strategy is actually prevention," she said.
But even if someone develops hypertension, maintaining a systolic pressure under 130 mmHg after age 40 can improve their cognitive outcomes. Here are some ways to manage hypertension:
• Stay active.
Lack of physical activity and a sedentary lifestyle are risk factors for hypertension and dementia. Conversely, getting regular exercise decreases the risk of both hypertension and dementia.
Gardening, doing yoga or just going for a walk can benefit both the brain and the rest of the body. Doing isometric exercises such as wall sits can be even more effective at reducing blood pressure than other forms of exercise.
• Eat healthier.
Excessive salt intake is a major dietary risk factor for hypertension. Reducing salt intake decreases blood pressure, in part from helping to improve the gut microbiome.
• Consider medication.
If you already have hypertension, it is still in your best interest to keep with the management strategy and lowering blood pressure, experts say.
Antihypertensive medications may help. Two meta-analyses of 17 total randomized control trials reported that antihypertensive treatment was protective against cognitive impairment and decline.
"We're really trying to just slow down additional target organ damage," she said. "The brain is just one of those organs that we're thinking about."
Richard Sima is a neuroscientist turned science journalist.
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