BOSTON – The sedentary young adults of today may be tomorrow’s cognitively impaired middle-aged adults, investigators suggested at Alzheimer’s Association International Conference 2013.
Young adults who are sedentary and stay relatively inactive through their early adult years are significantly more likely than are their more active peers to have worse executive function and processing speed in middle age, Tina Hoang, a research associate at Veterans Health Research Institute in San Francisco, said on behalf of researchers in the CARDIA (Coronary Artery Risk Development in Young Adults) study.
"We didn’t see an association with verbal memory, but we think that these findings suggest that physical inactivity earlier in the life course may be associated with worse cognitive outcomes later in life," she said.
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A lack of physical exercise among young adults could lead to cognitive impairment later in life, says Tina Hoang.
Although the mechanisms for the association are unclear, it is well documented that exercise decreases vascular risk factors, inflammation, and depression, and increases angiogenesis and neurogenesis, which may help to build up cognitive reserves early in the life course that can be drawn on in middle age, Ms. Hoang said.
The finding also suggest that the risks are cumulative, and that modifying cardiovascular risk factors in young adulthood may be warranted, said lead investigator Dr. Kristine Yaffe, professor of psychiatry, neurology, and epidemiology at the University of California, San Francisco.
"I think we can conclude that cardiovascular risk factors are probably very important modifiable risk factors, even early in life, for cognitive aging. But what does it mean in terms of public policy, how aggressive to be? I don’t think we really know," said Dr. Yaffe, also chief of geriatric psychiatry and director of the memory disorders clinic at the San Francisco VA Medical Center.
More longitudinal and life-course studies are needed, and it will be important for researchers to incorporate both biomarkers and neuroimaging into their studies to establish mechanisms of effect, she said.
In it for the long haul
In 1985 and 1986, black and white adults from the ages of 18 to 30 years in Birmingham, Ala.; Chicago; Minneapolis, Minn.; and Oakland, Calif., were recruited into the CARDIA longitudinal study and were followed for 25 years.
The final sample size of 3,375 participants included those with at least three assessments of physical activity and cognitive function by study year 25.
Low physical activity, the bottom quartile at baseline, was defined as less than 197 exercise units engaged in during leisure, occupational, and household activities for more than two-thirds of completed visits.
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Dr. Kristine Yaffe
The cutoff of 197 exercise units translates into approximately 100 minutes per week of moderate-intensity physical activity. The U.S. Department of Health and Human Services and the American Heart Association generally recommend that adults get at least 300 exercise units (150 minutes) per week, the investigators said.
Sedentary participants were those with fewer than 50 exercise units on more than two-thirds of completed visits.
Investigators assessed cognitive function with the Digit Symbol Substitution Test (DSST, standard deviation [SD] = 16.16), Stroop Interference Score (S = 10.98), and Rey Auditory Verbal Learning Test (RAVLT, SD = 3.27).
The authors found that on the DSST, 14.9% of those with moderate activity levels or greater were deemed to have cognitive impairment, compared with 20.9% of those with low activity levels. In a regression analysis adjusted for age, race, sex, education, smoking, body mass index, and hypertension, low activity on the DSST had a statistically significant odds ratio (OR) of 1.93 for cognitive impairment.
Similarly, 11.6% of the more active participants were judged cognitively impaired on the STROOP test, compared with 18.9% of their less active peers (adjusted OR 1.40).
Results of the RAVLT were not significantly different between the high- and low-activity groups.
The investigators are planning to develop objective measures of sedentary behavior and physical activity, and said they hope to study cognitive function over time, coupling the data to neuroimaging and biomarker studies.
The CARDIA study was supported by the National Heart, Lung, and Blood Institute. Dr. Yaffe disclosed receiving grant support from the National Institutes of Health, and serving as a consultant to Novartis and Eli Lilly. Tina Hoang reported having no financial disclosures.