Fran Lowry

November 29, 2010

November 29, 2010 ( UPDATED November 30, 2010 ) (Chicago, Illinois) — Walking might slow cognitive decline in both healthy adults and adults with mild cognitive impairment or Alzheimer's disease, according to a new study presented here at the Radiological Society of North America 96th Scientific Assembly and Annual Meeting.

The results, from an ongoing 20-year study, were presented by Cyrus A. Raji, PhD, from the University of Pittsburgh in Pennsylvania.

Dr. Raji and his team analyzed the relation between physical activity and brain structure in 426 people: 299 healthy adults (mean age, 78 years) and 127 cognitively impaired adults (mean age, 81 years). In the cognitively impaired group, 83 adults had mild cognitive impairment and 44 had Alzheimer's dementia. The subjects were recruited from the Cardiovascular Health Study.

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All subjects had 3D volumetric spoiled gradient echo magnetic resonance imaging of the brain. Voxel-based morphometry was used to analyze the relation between physical activity, as measured by the number of city blocks walked per week, and brain structure over time. The analysis controlled for potential confounders, such as body mass index, age, sex, education, and white matter hyperintensities.

The study found that greater amounts of physical activity were associated with greater volumes of frontal, occipital, temporal, entorhinal, and hippocampal regions 9 years later (P < .05), and that these relations held after controlling for all confounding factors.

For the healthy adults, 72 blocks over 2 weeks was the minimum distance necessary to spare gray matter volume; walking more than 72 blocks did not spare additional volume. For those who were cognitively impaired, walking 58 blocks, or about 5 miles per week, was sufficient to maintain brain volume and slow cognitive decline, the researchers found.

Sparing gray matter volume in the healthy aging group lowered the risk for future cognitive impairment by 50% over 13 years. In the cognitively impaired group, memory loss was reduced by more than 50% over 10 years, according to the researchers.

"These results demonstrate that walking at least 72 blocks in 2 weeks protects against gray matter volume loss in late adulthood and reduces the risk of experiencing cognitive impairment 13 years later," Dr. Raji said. "They also show that physical activity can slow the progression of Alzheimer's disease in people who already have it."

In an interview with Medscape Medical News, Dr. Raji said that walking might be protective because it preserves the integrity of the white matter in the brain. "People who walked more had better preserved white matter over time, as well as gray matter. That is important because if your white matter is intact, then your gray matter can communicate with itself and the preservation of function in the brain is a lot more intact."

The amount of walking needed to show this benefit is really quite modest, he noted. "It's a little less than a mile a day. It isn't a lot, and the effect didn't get any better if you walked 10 miles a week. All you had to do was get to the 5 miles per week threshold and you were able to achieve this effect, not only on the brain and the white matter, but also on cognitive function."

Nor did people have to be speedy walkers. "The speed of walking didn't make any difference at all. It came down to just how far you walked."

Any type of aerobic activity would probably have a similar effect, Dr. Raji added. The reason the investigators looked at walking was because it is the most accessible form of physical activity, regardless of age.

"The power of this idea is that if you engage in this regular physical activity, it benefits your brain down the line. Even if you have the horrible misfortune of getting Alzheimer's disease, your function is going to be better preserved and the progression of the disease isn't going to be as bad," he said.

A big limitation of the study is that it looked at walking at a single point in time. A better study would be to look at people who are physically active continuously for a certain time span — for example 10 years, Dr. Raji suggested.

"But I think it's safe to say that if these individuals were engaging in healthy physical activity in their 60s, it was probably a habit that they had acquired throughout their lives, and that starting that habit earlier is probably going to mean better results for your brain in the long term," he said.

Art Kramer, MD, director of the Beckman Institute for Advanced Science and Technology at the University of Illinois in Urbana, and an expert on the neurologic benefits of exercise, said that the study by Dr. Raji and colleagues "ties together, for the first time, self-reported physical activity to subsequent measures of brain volume and finally to clinical assessments of dementia. Previous studies have examined — and found — associations between 2 of 3 of these factors, but to my knowledge, this is the first study to link physical activity to brain volume and clinician assessments of dementia."

The study is limited because it is observational and so cannot establish causality among the examined variables. It also has a relatively small sample size. A third limitation is that it uses self-reported measures of physical activity rather than objective measures of cardiorespiratory fitness.

Despite these limitations, clinicians can still go ahead and give this message to their patients, based on the study results, Dr. Kramer said. "It's pretty straightforward. Physical activity, including walking, appears to be neuroprotective as we age."

This study was funded by the National Institute on Aging. Dr. Raji and Dr. Kramer have reported no relevant financial relationships.

Radiological Society of North America (RSNA) 96th Scientific Assembly and Annual Meeting: Abstract SSA17-01. Presented November 29, 2010.

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