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Harvard Commentaries
35320
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School


Man to Man Man to Man
 

Blood Pressure and Your Brain


January 24, 2013

By Harvey B. Simon M.D.

Harvard Medical School

High blood pressure is considered a cardiovascular disease because it involves the heart and blood vessels. High blood pressure (hypertension) is the leading cause of stroke. The higher your pressure, the higher your risk.

But since arteries are vital to the health of all our organs, hypertension is actually a threat to the whole body. Heart disease, heart failure and peripheral artery disease are among the dreadful results of untreated hypertension.

In many cases, hypertension's most damaging impact does not fall on the heart, but on the eyes, kidneys and especially the brain. It's increasingly clear that hypertension contributes to the risk of mild impairments in memory, thinking and judgment.

The good news is that treating hypertension protects your brain — and your heart. If you cut your usual blood pressure by just three points, you'll reduce your risk of stroke by 8%.

Stroke Facts

  • About 74 million Americans — 1 of every 3 adults — have hypertension. Many others have prehypertension.
  • Stroke is still the third most common cause of death in the United States. Each year, about 800,000 Americans have strokes; about 40% die and many people who survive are disabled.
  • Strokes have an annual price tag of about $74 billion.
  • Hypertension increases a man's risk of stroke by 220%.
  • Each 10 mm Hg rise in systolic pressure boosts the risk for ischemic stroke by 28% and for hemorrhagic stroke by 38%.
  • Ischemic strokes are the most common type of stroke. They make up 87% of the total number of strokes. They occur when an artery that supplies blood to the brain becomes blocked by a clot. Blockages of tiny arteries produce lacunar strokes.
  • Hemorrhagic strokes are a less common but more dramatic type of stroke. They occur when a blood vessel in the brain bursts. Blood spills into the brain or the fluid that surrounds it. Tiny hemorrhagic strokes are called microbleeds.

A single microbleed or lacunar stroke is not likely to produce symptoms. That's why they are called silent strokes. But a person who has multiple silent strokes over time can have major problems, including memory loss (cognitive dysfunction). The American Heart Association estimates that over 13 million Americans have had silent strokes.

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How Hypertension Can Affect Your Brain

High blood pressure doesn't only increase your risk of stroke. Although study results vary, the weight of evidence now suggests that high blood pressure takes a toll on the aging brain. It increases the risk of memory loss (mild cognitive impairment) and dementia (severe disturbances of memory, reasoning and judgment). There's even evidence that it adds to the risk of Alzheimer's disease.

Both systolic (top number) and diastolic (bottom number) hypertension contribute to the problem. In general, the higher the pressure and the longer it persists without treatment, the greater the risk of mental decline.

Most of these studies have focused on older adults. For example, a study of 2,505 men ages 71 to 93 reported that men with systolic pressures of 140 mm Hg or higher were 77% more likely to develop dementia than men with systolic pressures below 120 mm Hg. But a study that evaluated blood pressure and cognitive function in people ages 18 to 46 and 47 to 83 also found that high systolic and diastolic pressures were linked to cognitive decline over time in these age groups.

Since hypertension damages blood vessels, it's easy to see how it can contribute to a type of dementia called vascular dementia. This develops when small vessels in the brain become diseased or blocked. This deprives brain cells of the oxygen and sugar they need. If enough nerve cells are damaged or killed, memory can't be restored.

The link to Alzheimer's disease is less obvious. The problem begins with the accumulation of beta-amyloid, a small sticky protein that interferes with the function of nerve cells and eventually kills off cells, leaving a mass of tangles and plaques in its wake. In most cases, the part to the brain that is responsible for memory (the hippocampus) is hit the hardest. But new research suggests that vascular damage and tissue inflammation add to the injury.

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Can Treating Hypertension Help Prevent Dementia?

Doctors may be able to help ease the burden of dementia, but the damage and disability cannot be reversed. That makes prevention doubly important.

European scientists reported that long-term therapy to treat high blood pressure reduced the risk of dementia by 55%. Several American studies have also shown positive results:

  • One study linked treatment of high blood pressure to a 38% lower risk of dementia.
  • Another study reported that each year of treatment was associated with a 6% decline in the risk of dementia. In particular, men treated for 12 or more years enjoyed a 65% lower risk of Alzheimer's disease than men with untreated hypertension.
  • A team of investigators from Harvard and Boston University reported that six months of antihypertensive therapy actually improves blood flow to the brain, which explains the benefits observed in clinical research.

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How To Protect Your Brain

Even if you forget that hypertension is bad for your brain, remember that men with normal blood pressures live 5.1 years longer than men with hypertension.

Know your blood pressure. It seems obvious, but about 30% of people with hypertension don't know they have the disease. Be sure to have your pressure measured with each check-up and keep your own record so you can spot an upward trend as early as possible.

Know your goal. Even if you are just in the prehypertensive range (systolic pressure from 120 to 139 or diastolic pressure from 80 to 89), you should try to bring your pressure down to a normal reading below 120/80. People with hypertension can use somewhat less stringent targets. For otherwise healthy people, a reading below 140/90 is reasonable – but for patients with diabetes, chronic kidney disease, coronary artery disease, or atherosclerosis, the goal is below 130/80.

Modify your lifestyle. If you have hypertension, it's essential to change your lifestyle. Because lower blood pressure is better for health, anyone with blood pressure above 115/70 can benefit from these changes:

  1. A good diet can lower systolic blood pressure by 10 – 22 mm Hg. Reduce your sodium intake to less than 2,300 milligrams a day. The new, though stringent, goal for people with hypertension is 1,500 milligrams. This guideline also applies to healthy adults who are middle-aged and older, and for all African American adults. Reduce your intake of animal fat and processed foods, but chow down lots of fruits, vegetables, whole grains, and non- or low-fat dairy products.
  2. Moderate exercise, such as walking for 30 minutes a day, can lower your systolic pressure by 4 to 9 mm Hg or more.
  3. If you're obese, losing 20 pounds can drop blood pressure by 5 to 20 mm Hg over and above the benefits of diet and exercise.
  4. Light to moderate drinking — one to two drinks a day — won't raise your blood pressure, but heavy drinking will.
  5. Controlling stress is easier said than done in today's hectic world, but winding down can help you keep your pressure down.

Use medications if you need more help. A shocking 65% of patients with hypertension are above their target blood pressure numbers. Most experts recommend thiazide diuretics, angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers and calcium-channel blockers as first-line drugs. New research suggests that another old stand-by, the beta-blockers, may be less effective for preventing strokes. Doctors often start with a thiazide diuretic, but depending on your particular needs, another drug may be best. Therapy with two or more drugs may be required.

Work with your doctor to do whatever is needed to get your blood pressure to where it belongs. It will take some thought and effort, but it's the brainy thing to do.

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Harvey B. Simon, M.D. is an Associate Professor of Medicine at Harvard Medical School and a member of the Health Sciences Technology Faculty at Massachusetts Institute of Technology. He is the founding editor of the Harvard Men's Health Watch newsletter and author of six consumer health books, including The Harvard Medical School Guide to Men's Health (Simon and Schuster, 2002) and The No Sweat Exercise Plan, Lose Weight, Get Healthy and Live Longer (McGraw-Hill, 2006). Dr. Simon practices at the Massachusetts General Hospital; he received the London Prize for Excellence in Teaching from Harvard and MIT.

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