The brain is a vascular organ, which means that blood vessels (arteries, veins, and capillaries) carry blood to, from, and inside it. Arteries carry blood away from the heart, toward organs such as the brain. If those arteries become damaged or clogged, the brain is starved of the oxygen- and nutrient-rich blood that fuels nerve cells (neurons) and carries away waste. The result: brain function deteriorates and the risk of dementia increases.
“When arteries inside the brain lose elasticity or become twisted, blood doesn't flow through them as well,” says Lon White, M.D., of the Pacific Health Research Education Institute in Honolulu, HI. “As a result, the neurons that do your thinking don't get the oxygen or glucose they need to function properly.”
Picture an artery as a garden hose. Now, imagine pinching off sections of that hose; pressure increases and the flow slows down. This is similar to what happens to arteries over time. And just as a garden hose can eventually break down or burst under pressure, so can arteries. “It's really hard to keep the arteries intact and elastic for 100 years,” says Dr. White. Every time your heart beats, blood pumps through the arteries, creating pressure against their walls. Unfortunately, as we age, that pressure increases; as a result, the heart needs to work harder to pump blood to your organs.
“With each pulse of blood, your arteries have to expand like a python enveloping its prey. The smaller the artery is, the bigger the size of the pulse it takes,” says Dr. White. Over time, this process taxes the arteries, changing them in ways that decrease blood flow to the brain.
High blood pressure (called hypertension) occurs when too much stress is placed on the walls of the arteries. Sometimes called the silent killer, hypertension can occur without symptoms or major warning signs. (See box, “Know Your Numbers” and “Hypertension: The Warning Signs.”) But beneath the surface, the force required to pump blood throughout the body can wreak havoc on blood vessels.
The Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure recommends screening adults for high blood pressure every two years if their blood pressure is normally less than 120 mmHg (systolic)/80 mmHg (diastolic). Hovering above the normal range? Get checked more often.
- A normal systolic blood pressure is below 120.
- A systolic blood pressure of 120 to 139 indicates prehypertension (borderline high blood pressure).
- A systolic blood pressure number of 140 or higher is considered to be hypertension.
- A normal diastolic blood pressure number is less than 80.
- A diastolic blood pressure between 80 and 89 indicates prehypertension.
- A diastolic blood pressure number of 90 or higher is considered to be hypertension.
THE BRAIN UNDER PRESSURE
Blood pressure is measured by two numbers: systolic, which is the pressure on your arteries when your heart beats and pumps blood; and diastolic, which is the pressure in the arteries when your heart rests between beats. Normal pressure is 120 systolic over 80 diastolic. For the 50 million Americans diagnosed with hypertension, one or both of those numbers fall above the “normal” range.
Hypertension increases the risk of stroke, which can damage the brain. In one study, up to 30 percent of stroke survivors developed cognitive impairment in the first six months after their event; 9 percent developed dementia. Other studies suggest that having a stroke doubles the risk of cognitive decline.
But hypertension, even on its own, gradually diminishes blood supply to the brain and destroys neurons. Perhaps even more harmful are tiny injuries (microinfarcts) that act like pinpricks in your garden hose.
Hypertensive Crisis: The Warning Signs
According to the American Heart Association (heart.org), when blood pressure readings soar to dangerously high levels (systolic of 180 or higher or diastolic of 110 or higher), obvious symptoms may occur. Blood pressure this high, known as hypertensive crisis, requires emergency medical treatment. (In other words, call 9-1-1.) A person in hypertensive crisis may experience:
- Rapid pulse
- Shortness of breath
- Visual disturbances
These microinfarcts may be unnoticeably small, resulting in only temporary, partial blockages of blood supply. Over time, however, more areas of the brain can become damaged, leading to memory loss, confusion, and other signs of dementia.
“People with this kind of damage often have difficulties with executive function like planning and multi-tasking,” explains Vladimir Hachinski, M.D., D.Sc., professor of neurology and epidemiology at the University of Western Ontario in Canada and Fellow of the American Academy of Neurology (AAN).
Trouble is, most people don't worry about dementia until in their senior years. According to Dr. White, that's often too late: untreated hypertension during midlife can result in serious damage, he says.
Studies show that people in midlife who have chronic uncontrolled hypertension are more likely than people with normal blood pressure to develop Alzheimer's disease (AD). Others have found accelerated brain aging among hypertensive and pre-hypertensive individuals in their 40s.
These studies suggest that damage to the brain's blood vessels develops gradually over time and eventually has clear effects on thinking. Yet, many people don't even realize they're at risk. Some develop hypertension in their 20s and 30s that goes undetected for more than a decade.
The good news: people can influence their late-life brain health by knowing and treating their blood pressure—even at a young age, when they wouldn't necessarily be thinking about it.
MEDICATIONS ON THE BRAIN
Scientists have long known that managing blood pressure is critical to long-term brain health. A 2009 analysis in the American Journal of Geriatric Pharmacotherapy reviewed 65 studies published between 1999 and 2008, concluding that antihypertensive medications—particularly ACE inhibitors and diuretics—helped reduce the risk for and progression of dementia. And a study by Chinese scientists published in 2011 in the Brain Research Bulletin reported that treatment with beta-blockers reduces the prevalence of AD and delays functional decline.
Most recently, a study presented at the AAN Meeting in San Diego this spring suggests that beta-blockers in particular may offer a cognitive edge, and not just because they reduce blood pressure.
For the study, Dr. White and his colleagues used data from the Honolulu-Asia Aging Study (HAAS), a community-based study of 2,285 Japanese-American men. The men were between the ages of 71 and 73 and had been diagnosed with hypertension but not dementia when they enrolled in the study.
Researchers examined the brains of 774 autopsied men, 610 of whom had been treated with antihypertensive drugs; only 40 had been treated with beta-blockers alone. The researchers found that men who took beta-blockers without any other antihypertensive medications had fewer brain abnormalities than those who took other antihypertensive drugs. What's more, men who were treated with a combination of medications that included beta-blockers were cognitively better off than those not treated with beta-blockers at all.
The HAAS study was the first to identify beta-blockers as superior to other antihypertensives in terms of preventing microinfarcts, brain atrophy, and the type of damage linked to AD. While researchers aren't clear on the underlying mechanisms responsible for these findings, they do have a few theories.
Staving Off Dementia: What You Can Do
- GET MOVING: Research suggests that even a 30-minute daily walk can reduce the risk of dementia and help slow its progression. Any activity that gets your heart pumping and your blood circulating will not only reduce your risk of dementia, it will also boost your overall health and happiness.
- MIND YOUR PLATE: A diet of fruits, vegetables, fish, nuts, and whole grains (also known as the Mediterranean diet) has been linked to a lower risk of hypertension and stroke. Eating this way not only helps control weight, but it also supplies the antioxidants needed to support healthy blood vessels. (For more on the Mediterranean diet, go to http://bit.ly/13EU8NV.)
- HAVE MORE FUN: Laughing, playing, and enjoying yourself lowers stress levels and inspires lifestyle changes that may help prevent cognitive losses.
- TAKE A BREATH: Stress is a major contributor to hypertension and heart disease. Take time out every day to practice relaxation techniques, such as deep breathing, yoga, and meditation.
- CHALLENGE YOUR BRAIN: The brain is plastic, meaning it's capable of creating new connections based on new experiences. Learning new languages, playing a musical instrument, or taking up a new sport can help build brain capacity.
“Beta-blockers, more than other anti-hypertensive drugs, reduce heart rate and physical responses to stress,” says Dr. White. “My assumption in starting this was that beta-blockers, by virtue of reducing pulse rate and pulse pressure, would reduce exposure to the mechanical trauma of hypertension.”
Interestingly, in Dr. White's study, use of beta-blockers was associated not only with a lower frequency of microinfarcts but also the changes of AD. That, says Dr. Hachinski, may be a product of increased blood flow to the brain, which improves clearance of toxic protein deposits involved in AD.
“Beta-blockers are the only antihypertensive drugs that increase blood flow at higher doses,” says Dr. Hachinski. So if dementia is due in part to less efficient blood flow to the brain, then beta-blockers would be more protective than other antihypertensive drugs in terms of fueling the brain with oxygen and nutrients, he says.
But before you rush off to fill a prescription for beta-blockers, scientists caution these findings are preliminary and shouldn't change the way physicians treat hypertension. People who have asthma, diabetes, or high cholesterol and triglyceride levels may not be appropriate candidates for beta-blockers.
In addition, the numbers involved in the study are small, and the results represent only a small subset of people: elderly Japanese-American men. “The findings are of great interest and potential importance, but we should be cautious about over-interpreting the results. We don't know if the findings will apply to other populations as well,” says Philip B. Gorelick, M.D., M.P.H., medical director and vascular neurologist at the Hauenstein Neuroscience Center in Grand Rapids, MI. “Plus, the HAAS study based its results on brain lesions found at autopsy, so it only reflects a snapshot of the brain at the end of life, not changes or lack of changes in the brain over time, which could be revealing.”
While the lower heart rate and increased blood flow caused by beta-blockers may be beneficial for some patients, others—such as those who exercise—might experience serious side effects. “If you're an athlete or a runner, it's dangerous to take beta-blockers because they don't allow your heart rate to pick up during exercise,” explains Dr. White.
Perhaps even more important, argues Dr. Gorelick, some beta-blockers have been associated with blood pressure variability, which can negatively affect brain structure and function, potentially impairing cognitive function.
With the advent of myriad drugs deemed more effective, it's no wonder that beta-blockers, once the preferred treatment for hypertension, have taken a back seat.
GO WITH THE FLOW
If you want to stave off dementia and enhance quality of life, controlling blood pressure is key, especially during midlife when the damaging trajectory begins. The goal, say experts, is to preserve the health of your heart and blood vessels, maximizing the circulation of oxygen- and nutrient-rich blood to the brain—sort of like widening the garden hose so water can flow freely.
Most importantly, keep blood pressure levels in check. Excessively high or low blood pressure can harm brain blood vessels and tissues and increase your risk of stroke. Manage conditions like diabetes, which can injure blood vessels that nourish brain cells. And if you smoke, stop. Smoking injures blood vessel walls and speeds up the process of hardening of the arteries.
Challenging your body and mind also seems to be important.
“You want to do something more than just sit on your fanny and exercise your right arm drinking beer. You want to exercise your whole body,” says Dr. White. “It's the same thing with your brain. The more you use your whole brain, and the more effectively you can use it, the sharper you'll be.”