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Published on: July 19, 2011
by Helping You Care:
Two studies published today in the Archives of Internal Medicine, a journal of the American Medical Association, have found that engaging in regular physical activity is associated with less decline in cognitive function in older adults. In fact, one of the studies found that 30 minutes of brisk walking every day may produce effects equivalent to making you “cognitively younger by 5 to 7 years.”
These articles appear in the July 19, 2011 online issue of theArchives of Internal Medicine, coinciding with their presentation at the International Conference on Alzheimer’s Disease being held in Paris.
The French Study
In one study, entitled “Physical Activity and Cognition in Women With Vascular Conditions,” Marie-Noël Vercambre, Ph.D., from the Foundation of Public Health, Mutuelle Generale de l’Education Nationale, Paris, and colleagues, analyzed data from 2,809 women aged 65 or older who participated in the Women’s Antioxidant Cardiovascular Study. The participants in this study included women who had either prevalent vascular disease or three or more coronary risk factors.
In background information, the study authors noted that “Individuals with vascular disease or risk factors have substantially higher rates of cognitive decline, yet little is known about means of maintaining cognition in this group.” The researchers examined the study data to determine the relation between physical activity and cognitive decline in these women.
Methodology. The researchers determined the patients’ physical activity levels at baseline (1995 to 1996) and every two years thereafter, by asking the participants questions about their average weekly time spent on several different physical activities during the past year, and the intensity of their activities.
Based on the responses the researchers estimated the energy expended by each participant in “MET hours per week.” The “MET hours” measurement referred to a value for “metabolic equivalent of task” assigned by the researchers to each physical activity and its intensity. For example, 1 MET was defined as the energy expended while sitting quietly. The MET values assigned included: 12 MET for running, 8 MET for stair-climbing, 7 MET for jogging, racquet sports, lap swimming, and bicycling, 4 MET for yoga, stretching or toning, 2.5 MET for walking at an easy pace, and 4.5 MET for walking at a brisk pace. The researchers estimated the energy expended in physical activity per week by multiplying the MET value of each reported activity by its duration. They reported that, among the sample, walking was the most common physical activity, and “accounted for about half of the total energy expenditure.”
To measure cognition at baseline (between 1998 and 2000), the researchers conducted telephone interviews with the 2,809 women, which included a battery of five tests of global cognition, verbal memory and category fluency. These tests were repeated three more times over the 5.4 year follow-up period. Each time, the researchers measured the rate of change in the global cognition composite score. They also measured changes in the verbal memory composite score and the category fluency score. “Verbal memory is one of the best predictors of Alzheimer disease, and category fluency partly measures executive function, which is associated with vascular dementia,” they noted.
The researchers analyzed the data for correlations between cognitive score changes and level of total physical activity and energy expenditure.
Findings. The researchers found that as participants’ energy expenditure increased, their rate of cognitive decline decreased significantly. “More active women tended to have better cognitive scores over time, and the difference in performance by physical activity level widened over time,” the authors stated.
They found significantly lower levels of global cognitive decline in women beginning with those in the “fourth and fifth quintiles of total energy expenditure” (which was equivalent to walking 30 minutes or more every day at a brisk pace), compared to those in the first quintile of energy expenditure (those least active), and these differences were statistically significant.
Using the known effect of age on cognitive decline as a benchmark, the researchers reported that:
“The mean difference in rates of cognitive decline between the first and fourth quintiles of physical activity was equivalent to the mean difference found for women 5 years apart in age, and the mean difference between the first and fifth quintiles was equivalent to 7 years of age. That is, the apparent cognitive benefits associated with physical activity levels, such as walking 30 minutes or longer every day at a brisk pace, were equivalent to being cognitively younger by 5 to 7 years.”
In addition, the authors reported, “Most important, the association with total physical activity was not restricted to women engaged in vigorous exercise; higher levels of walking for exercise were significantly related to less cognitive decline.”
Explanations. As potential explanations for how exercise may slow cognitive decline, the authors stated:
“Various biologic mechanisms may explain the positive relation between physical activity and cognitive health. Exercise may directly preserve neuronal structures by stimulating brain-derived neurotrophic factor and neuronal growth, possibly providing reserve against cognitive decline and dementia. Exercise may also have indirect effects by strengthening the underlying systems that support brain plasticity and helping to sustain the brain’s vascular health by beneficially influencing cardiovascular risk factors, promoting endothelial function, improving glucose and insulin regulation, and ensuring adequate cerebral perfusion. Furthermore, physical activity reduces inflammation, which is higher in those with vascular disease and impairs systemic and brain-specific growth factor signaling. Physical activity may also improve psychological well-being, which in turn may protect against decline in cognitive functioning.”
Conclusion. In conclusion, the study authors stated:
“In summary, we found clear and strong associations between greater physical activity and reduced cognitive decline in this population of women with vascular disease or coronary risk factors. If confirmed in future studies, physical activity recommendations could yield substantial public health benefits given the growing number of older persons with vascular conditions and their high risk of cognitive impairment.”
The Canadian Study
In the other study, entitled “Activity Energy Expenditure and Incident Cognitive Impairment in Older Adults,” Laura E. Middleton, Ph.D., from the Heart and Stroke Foundation Centre for Stroke Recovery, Sunnybrook Research Institute, Toronto, and colleagues, examined data from 197 men and women with an average age of 74.8 years who participated in the Health, Aging, and Body Composition study, an ongoing “prospective cohort” study. The participants had no mobility or cognitive problems when the research began in 1998 to 1999.
Methodology. The researchers measured participants’ cognitive function at the beginning of the study and again two to five years later, with the Modified Mini-Mental State Examination (MMMSE). They defined “cognitive impairment” as a decline of at least 9 points between baseline and follow-up evaluations.
During the study, the researchers measured participants’ total energy expenditure by using doubly labeled water, a technique that provides evidence of how much water a person loses and thereby serves as an objective measure of metabolic activity. The authors calculated the participants’ Activity Energy Expenditure (AEE), which they defined as 90 percent of total energy expenditure minus resting metabolic rate.
Findings. After adjustments to the participants’ baseline MMMSE scores for demographics, fat-free mass, sleep duration, self-reported health and diabetes mellitus, the researchers found that participants who had the highest AEE scores (Activity Energy Expenditure), tended to have lower odds of incident cognitive impairment.
The authors also found that there was a “significant dose response” between AEE and incidence of cognitive impairment, meaning the more Activity Energy Expenditure, the less cognitive impairment.
Conclusions. In conclusion, the authors stated:
“Our study provides new evidence that objectively measured total daily activity, as measured by energy expenditure, is associated with a reduced incidence of cognitive impairment in older adults. The contribution of moderate and vigorous physical activity vs low-intensity physical activity to this relationship remains unclear; future longitudinal studies should examine the role of moderate and vigorous physical activity vs low-intensity physical activity in maintaining cognitive independence for older adults. We are optimistic that even low-intensity activity of daily living may be protective against incident cognitive impairment.”
Commentary: Brains and Aging
In a commentary accompanying the studies, entitled, “Brains and Aging,” also published in the July 19, 2011 issue of The Archives of Internal Medicine, Eric B. Larson, M.D., M.P.H., from Group Health Research Institute, Seattle, notes that these studies serve to “buttress growing evidence that habitual physical activity and fitness are associated with age-related changes in cognition and risk of dementia.”
He observes that the findings of the Vercambre and colleagues study are especially significant in that the women in the study were older and had vascular risk, and, he writes, “older women with high levels of vascular risk constitute a major risk group and that vascular risk is linked to cognitive decline.” Therefore, the finding that exercise can reduce cognitive decline in this high risk group is especially significant.
The Middleton and colleagues study, Larson observes, is significant in that, “The fact that the study used a validated measurement of energy expenditure, not just self-report, makes the results of further importance.” Such research, he states, is increasingly needed as the population ages and the health care field attempts to cope with higher rates of cognitive decline.
Larson suggests that studies such as these “highlight a gradual but steady change in current thinking about risk factors for late-life dementias.” This gives hope that cognitive impairment in older adults due to vascular factors can be reduced, because vascular risk factors such as limited physical activity are modifiable.
“I believe that these findings can inform practice and the advice that we give our aging patients,” comments Larson. “We can tell them that ongoing maintenance of physical activity is definitely worthwhile and likely of increasing benefit as they advance into old age.” In addition, Larson stresses the need for research into “programs that promote ongoing physical activity, especially in late life.”
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