WASHINGTON, DC—Persistently low levels of physical activity and high amounts of television viewing in early adulthood were associated with poor executive function and processing speed in midlife, according to research presented at the 2015 Alzheimer’s Association International Conference. The findings suggest that these modifiable risk behaviors may be important targets for dementia prevention, said Tina Hoang, MSPH, of the Northern California Institute of Research and Education in San Francisco.
Prior studies have found that physical activity in later life may be protective of dementia, but studies in younger adults often focus on the acute benefits of physical activity rather than the long-term effects. To examine how long-term patterns of physical activity and television viewing in early adulthood are associated with cognitive performance at midlife, Ms. Hoang and her research colleagues analyzed data from the Coronary Artery Risk Development in Young Adults (CARDIA) study.
25 Years of Follow-Up Data
CARDIA is an ongoing prospective study of black and white adults who were between ages 18 and 30 when they enrolled in the study in 1985 and 1986. CARDIA researchers assessed participants’ physical activity and television viewing at each visit using a validated questionnaire that asked participants about 13 types of moderate and vigorous intensity activities, including exercise, leisure, occupational, and household activities. Participants also reported the number of hours per day they watched television. Low physical activity was defined as activity below the bottom quartile of baseline levels (approximately three 50-minute sessions of activity per week). High television viewing was defined as time above the top quartile of baseline levels (more than four hours per day). A long-term pattern of each behavior over 25 years was defined as meeting those cutoffs for more than two-thirds of follow-up visits. Researchers assessed cognitive function at year 25 in the study using the Digit Symbol Substitution Test (DSST), Stroop interference test, and Rey Auditory Verbal Learning Test (RAVLT).
Likelihood of Poor Performance
Ms. Hoang and her coinvestigators included in their study sample 3,247 participants who had at least three follow-up visits over 25 years. Seventeen percent of participants reported a long-term pattern of low physical activity. Participants who reported low physical activity were more likely to be female, less likely to be white, had lower education, drank less alcohol, and were more likely to have hypertension. Investigators used logistic regression to examine the association with midlife cognitive function. Compared to participants with higher levels of physical activity, those with low physical activity had an increased likelihood of poor performance (ie, more than one standard deviation below the mean) on the DSST (adjusted odds ratio [aOR]=1.82) and the Stroop test (aOR=1.38), but not the RAVLT, after adjusting for age, race, sex, education, smoking, alcohol, BMI, and hypertension.
Eleven percent of the study participants reported a long-term pattern of high television viewing. Those participants also had an increased likelihood of poor performance on the DSST (aOR=1.34) and the Stroop test (aOR=1.61), but not on the RAVLT. Three percent of the study participants reported high levels of television viewing and low levels of physical activity. Those participants, compared with participants who had persistently high levels of physical activity and low levels of television viewing, were more than twice as likely to perform poorly on the DSST (aOR=2.45) and the Stroop test (aOR=2.38). According to Ms. Hoang and her coinvestigators, one limitation of the study was that equivalent tests of cognitive function were not conducted in early adulthood.
Public Health Implications
The findings demonstrate that early and middle adulthood may be critical periods when physical activity may promote healthy cognitive aging, said Ms. Hoang. Public health efforts that increase physical activity and reduce sedentary behavior in childhood and early adulthood may significantly affect cognitive function later in life, said study investigator Kristine Yaffe, MD, Professor of Psychiatry, Neurology, Epidemiology, and Biostatistics and the Roy and Marie Scola Endowed Chair in Psychiatry at the University of California, San Francisco.
“What’s happening in midlife, in one’s 50s, is setting the stage for what’s happening over the next 20 or 30 years,” said Dr. Yaffe. The researchers are interested in following this cohort to see how these factors affect the risk of dementia and Alzheimer’s disease in the next 10 to 20 years, she said.