Blood Pressure and the Brain

The next time a nurse inflates a blood pressure cuff around your bicep, pay attention. Those numbers are not just important for your heart, but for your brain as well.

It's becoming increasingly clear that high blood pressure, or hypertension, is at the root of much cognitive decline that has previously been attributed to aging. The more that scientists scrutinize brain function, and especially memory, the more they conclude that we have the ability to keep our memory and spirit strong well into old age. But it depends on how well we nourish our brain throughout life.

Hypertension is defined as blood pressure of 140/90 or above. The first number is the measurement of the blood's force against artery walls when the heart is beating. The second number is the pressure between beats. A person is hypertensive if either number is too high.

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Most people think salt is the culprit in high blood pressure. In the vast majority of hypertensives, salt isn't the root of the problem. Only about one third of people with high blood pressure are what doctors call "salt sensitive."

"The rest of the folks can eat all the salt they want without seeing much change in their blood pressure," says Shari Waldstein, Ph.D., associate professor of psychology at the University of Maryland at Baltimore County, who studies the cognitive consequences of hypertension. People whose diets are not to blame can pinpoint the problem through a trial of medications that target differing pathways in the body. Blood pressure is affected by many of the body's systems, including kidney function, hormones such as insulin and the sympathetic and parasympathetic nervous systems.

Regardless of cause, high blood pressure is extremely dangerous, especially for people who don't know they have it, typically people who rarely see a doctor. Hypertension has few symptoms; some sufferers complain of headaches, nosebleeds or shortness of breath but for the most part the body suffers in silence.

High blood pressure does its damage by weakening the blood vessels, over time leading the inner lining to slough off. Vessels can be weakened to the point that they tear, causing sudden death or disability via a stroke or aneurysm. Hypertension can also lead to heart attacks.

But long before it creates a health emergency, hypertension takes a subtle toll on mental faculties. It can reduce attention, learning, memory and decision-making skills in ways that can be clearly seen in studies.

"Generally, whatever problems impact cardiovascular health also affect cognitive functioning," says Merrill Elias, Ph.D., a professor of epidemiology at Boston University who has studied hypertension for 35 years.

Indeed, some researchers now believe that a substantial amount of age-related mental decline has little to do with age and much to do with blood pressure. Waldstein says there's a large body of research linking hypertension directly to brain function, but scientists don't yet know how it causes damage at the cellular level.

Elias says high blood pressure exerts a constant stress on the brain and cardiovascular system that appears to be cumulative. "It's more of a problem for people who don't go to the doctor," he says. "Just think of it as your brain taking a hit every day."

The damage to the brain can come in a variety of forms. In the elderly, more than half of whom suffer from hypertension, the damage can be detected on MRIs in the form of "white matter lesions." These are pinpoint lesions in the brain's message-carrying axons that affect cognitive function, especially weakening memory and reasoning and significantly impacting quality of life.

High blood pressure can also cause small strokes that may go unnoticed, but which diminish the brain's capacity to function. Other people who have chronic hypertension actually have small spots on their brain where the tissue is dead, says Elias.

But that doesn't mean that high blood pressure is a disease of old age. For one thing, many people who are in their 20s and 30s suffer from it as well. It's especially important for younger people to control their blood pressure so that the damage doesn't start early and snowball over time.

But neither is high blood pressure inevitable with age. Blood pressure can be kept in check by keeping cholesterol low, not smoking and limiting salt. But perhaps the most important factor is keeping obesity at bay, a struggle most Americans are not winning.

"Weight is a biggie," says Elias. "The more you weigh, the more pressure there is."

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