Exercise May Beat Mental Activity in Preserving Cognition
More evidence has linked exercise with a positive effect on the brain. A new study finds that older adults who reported being the most physically active had less brain atrophy, higher volumes of gray matter, and less damage to white matter compared with their more sedentary counterparts.
Not only was the sample size, at almost 700 participants, much larger than those of other studies looking at the effect of physical activity on the brain, but this study is the first to look in detail at the effect of exercise on white matter, the brain's "wiring," .lead author Alan J. Gow, PhD, senior research fellow, Center for Cognitive Aging and Cognitive Epidemiology, University of Edinburgh, United Kingdom, told Medscape Medical News.
"That's probably one of the unique aspects of the study, the focus on the wiring, as well as on the volumes and shrinkage of actual gray matter."
However, the researchers found no association between social and mentally stimulating leisure activities and these brain changes.
The study is published in the October 23 issue of Neurology.
Activity Range
The current analysis included data on 691 participants in the Lothian Birth 1936 (LBC1936), a longitudinal study of aging in participants born in 1936. Participants were recruited at a mean age of 69.5 years and had a second assessment 3 years later at a mean age of 72.5 years (the assessments are referred to as wave 1 and wave 2).
All the participants had had an IQ test at age 11, as part of a nation-wide educational survey. At wave 1, they completed a questionnaire that rated their participation in activities on a 6-point scale, ranging from no exercise or only doing necessary household activities to keeping fit or heavy exercise several times a week. Participants also rated their frequency of participation in 15 social and intellectual leisure activities.
At wave 2, researchers obtained structural brain measures through magnetic resonance imaging.
The study showed that a higher level of physical activity was associated with a higher fractional anisotropy, larger gray and normal-appearing white matter (NAWM) volumes, less atrophy, and lower white matter lesion load, the authors note.
The association of physical activity with atrophy, gray matter, and white matter lesion remained significant after adjustment for covariates that included age, social class and health status, they added.
"For example, physical activity (standardized β = -0.09, nonstandardized β = -0.09, p = .029) and stroke (standardized β = 0.18, nonstandardized β = 0.69, p = .003) each had an independent effect on rated WML load," they write.
Leisure activity was associated with NAWM volume but was nonsignificant after inclusion of covariates.
White Matter Damage
Because the effect of physical activity on white matter lesion volume survived adjustments for all covariates, a reduced white matter lesion burden might be one advantage of a physically active lifestyle, said the authors.
"Interestingly, physical activity was associated with the indicator of white matter damage but not with NAWM volume in the fully adjusted models," they write. "This might indicate any putative protective mechanisms works via reducing lesion occurrence though a detailed examination the effect of physical activity on white matter is required."
Although the study linked physical activity with less brain atrophy overall, male participants had higher levels of atrophy than women. "This might purely be the result of the fact that men in general don't live as long as women" and any structural brain changes might be more visible in men than in women at that age, said Dr. Gow.
The current study doesn't provide insight into how exactly being physically active might influence brain structures, but researchers speculate that blood pressure effects on exercise capacity might help explain the relationship. "If indeed it is physical activity that protects the brain, we need to know much more about how that happens, the pathway, whether it's something to do with the reduction in the cardiovascular risk profile overall or a natural direct effect on the brain," said Dr. Gow.
The study only investigated the effect of current physical activity, at age 70 years, not past activity. "I would agree that we need to know much more about the life course of physical activity and at what point it might have the most beneficial effect," said Dr. Gow.
Leisure Activity
There was no association between leisure activity and any of the assessed structural parameters in the fully adjusted models, a finding that Dr. Gow didn't find surprising.
"People who are most likely to do challenging intellectual activities are able to do them, so it might be that the activities themselves aren't protective but the association is driven by the fact that the people who do them are the least likely to be showing declines," he said.
That's not to say that people should stop participating in such activities, as they might benefit the brain in some way and they affect quality of life, provide pleasure, and influence well-being. But getting more physical exercise might be more important when it comes to maintaining structural brain health, said Dr. Gow.
It's possible that the study results could be explained by participants whose white matter integrity was declining or who had significant atrophy becoming physical inactive. Dr. Gow is keen to complete the next 3-year assessment of the cohort (at age 76 years), which should provide more information about the cause-and-effect relationship.
"We're interested in aging and how the brain and general health change over time, and we need to follow the same people for a long period of time so we can tease out all these questions."
Host of Studies
Asked to comment, John Hart, Jr, MD, medical science director, Center for BrainHealth, professor, Behavioral and Brain Sciences, University of Texas, Dallas, and a member of the American Academy of Neurology, said this is another in a "whole host of studies coming along" investigating the impact of physical activity on the brain.
What the study has going for it is its relatively large sample size and its inclusion of multiple types of brain measures in terms of metrics, said Dr. Hart. "And it did show that physical exercise to a reasonable degree can actually change brain physiology and or structures."
But a drawback of the study is that it couldn't explain causation. "It doesn't explain anything in great detail in terms of what, how, where, when, and why, said Dr. Hart.
He didn't place much weight on the lack of association found between leisure activities and structural brain changes because of the retrospective nature of the analysis. "There's a fair amount of error when you ask subjects retrospective questions," without anything being documented or in the absence of a closely watched time period, he said. "People's self estimates don't always have the greatest accuracy."
He said he's curious about whether the structural brain changes remain when physical activity stops. He's convinced that exercise is probably not like an antibiotic that, taken once, gets rid of an infection. "I think this is a chronic kind of thing; if you want to maintain these changes, you have to keep doing it," he said.
Dr. Hart would also like to learn more about the importance of timing of exercise. "I'm betting that there's a 'never too late,' but it's a law of diminishing returns," he said.
As an expert in the brain and cognition, Dr. Hart is often asked how to prevent cognitive decline. He believes he has a recipe for warding off dementia, something that anyone can do as long as it's not contraindicated.
"As a general rule of thumb, it's getting to an aerobic state, so raising your pulse 20 beats above your baseline for 20 minutes continuously, at least 3 times a week."
The study was supported by Research Into Aging, the Age UK-funded Disconnected Mind Project and the United Kingdom's Medical Research Council. The study authors and Dr. Hart have disclosed no relevant financial relationships.
Neurology. 2012;79:1802-1808. Abstract
Medscape Medical News © 2012 WebMD, LLC
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