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Memory Special Report

Guarding Your Memory

What is the single most important thing people can do to protect their brains and guard their memory? In this article from the Johns Hopkins Memory Bulletin, Sandra Aamodt, Ph.D and Sam Wang, Ph.D answer this important question.

Q. What is the single most important thing people can do to protect their brains and guard their memory?

Sam: The answer is simple and surprising. It's physical exercise, especially the kind that raises your heart rate and makes you sweat. It's not known exactly why exercise works, but the best idea is that it improves blood flow to the brain. It also stimulates the secretion of neurotrophins, which are signaling molecules that help neurons grow.

A recent meta-analysis of 18 studies reports that a physical exercise program -- even one started when people are in their 70s -- can significantly boost executive function. In this case, the effect size is quite large. To return to our example, if you are an average person out of a group of 20, which would rank you as number 10, exercise can improve your rank to number five -- a huge improvement.

Sandra: What's important to remember is that there have been actual intervention studies reporting that exercise programs can significantly improve executive function and the ability to plan and execute behaviors. A meta-analysis of 18 studies published in Psychological Science concluded that a variety of physical exercise programs improved executive function substantially. Another study, published in the Journal of the American Geriatrics Society, found evidence that exercise also protects cognitive ability.

Older people who had better aerobic capacity -- meaning they were in better physical condition at the beginning of the study -- were most likely to have maintained their level of cognitive functioning six years later. People who were otherwise healthy but had poor aerobic capacity had worse cognitive scores after six years.

Physical fitness also influences brain volume. In a study published in the Journal of Gerontology, researchers asked people ages 60–79 to either walk or perform stretching and toning exercises for one hour three times per week for three months. A third group did not exercise. The researchers used magnetic resonance imaging (MRI) to measure the participants' brain volumes before and after the exercise programs. After three months, brain volume had increased significantly among the people who had walked. The biggest increases were in the frontal lobes, the area of higher-order mental activity like memory and attention. Brain volume did not change in the other two groups.

Q. How much exercise is needed for optimal memory and brain preservation and brain health?

Sam: The meta-analysis of exercise programs and executive function found that 30 minutes of moderate activity three times per week had significant benefits for brain health. The U.S. Surgeon General and most health organizations recommend at least 30 minutes of moderate activity on most days of the week to maintain good health.

Brisk walking is a popular aerobic exercise that has been found to reduce the risk of cognitive decline. In a study published in the Journal of the American Medical Association, researchers asked 2,257 men (ages 71–93 and with no signs of dementia) how far they walked each day. Cognitive assessments performed four to eight years later showed that the men who walked less than a quarter mile a day were nearly twice as likely to have developed dementia as those who walked two miles or more each day.

In the same issue of the journal, a study of 16,466 women found that regular exercise (including walking) reduced the risk of cognitive impairment by 20%, and the more exercise, the better. Women who exercised at least 1.5 hours per week showed less cognitive decline than those who walked 40 minutes or less each week.

Sandra: If you do a half hour to 45 minutes of exercise three times a week, you are well into the effective range. You don't have to spend an enormous amount of time exercising to benefit. Although there's no statistical evidence right now that more exercise would be any better for your brain, it wouldn't hurt. I think we could say with some confidence that it would be better for your heart, so my best guess is that it would be better for your brain, too.

Q. What's the link among exercise, stroke, and memory protection?

Sam: Exercise can dramatically reduce your risk of stroke, which is the brain equivalent of a heart attack. In the most common type of stroke, a blocked blood vessel prevents blood flow to a particular brain region, leading to neuron death and dysfunction. If you survive a stroke, you have a significantly increased risk of cognitive impairment, memory loss, and AD. A report from the Archives of Neurology showed that people with a history of full-blown stroke were about 60% more likely to receive a diagnosis of Alzheimer's disease than were those with no history of stroke.

If you have significant risk factors for stroke -- such as hypertension, diabetes, and smoking -- you may have an increased risk of declines in executive function, according to a study published in Stroke that assessed the 10-year risk of stroke in more than 2,000 men and women. Obviously, a major stroke -- for instance, one in which you get a big clot in a big vessel that cuts off blood flow to a significant portion of your brain—can have a major effect on brain function and memory. But so can so-called microstrokes, which are caused by little blood clots that lodge in little vessels and deprive a small part of your brain of blood. A lot of older people have microstrokes, which are a risk factor for subsequent major strokes.

Most people don't even notice microstrokes, which usually affect only a small number of brain cells. Although microstrokes sometimes show up as tiny spots on brain scans, other times they can't be picked up at all. The bottom line is that there's no way to interpret killing off of neurons as being a good thing, even in small numbers. So it seems pretty obvious that doing anything you can to prevent microstrokes -- especially engaging in regular physical exercise -- is essential for protecting your brain and guarding your memory.

Posted in Memory on May 18, 2009

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