How much TV you watch as a young adult may affect midlife cognitive function

Few studies have investigated the association between physical activity in early adulthood and cognitive function later in life. Coupled with the increasing prevalence of sedentary or screen-based activities, such as watching television, these trends are of concern for upcoming generations of young people.

Tina D. Hoang, M.S.P.H., of the Northern California Institute for Research and Education at the Veterans Affairs Medical Center, San Francisco, Kristine Yaffe, M.D., of the University of California, San Francisco, and coauthors examined associations between 25-year patterns of television viewing and physical activity and midlife cognition.

The study of 3,247 adults (ages 18 to 30) used a questionnaire to assess television viewing and physical activity during repeated visits over 25 years. High television viewing was defined as watching TV for more than three hours per day for more than two-thirds of the visits and exercise was measured as units based on time and intensity. Cognitive function was evaluated at year 25 using three tests that assessed processing speed, executive function and verbal memory.

Participants with high television viewing during 25 years (353 of 3,247 or 10.9 percent) were more likely to have poor cognitive performance on some of the tests. Low physical activity during 25 years in 528 of 3,247 participants (16.3 percent) was associated with poor performance on one of the tests. The odds of poor cognitive performance were almost two times higher for adults with both high television viewing and low physical activity in 107 of 3,247 (3.3 percent) participants, according to the results.

The authors acknowledge a few limitations, including possible selection bias and that physical activity and TV viewing were self-reported.

"In this biracial cohort followed for 25 years, we found that low levels of physical activity and high levels of television viewing during young to mid-adulthood were associated with worse cognitive performance in midlife. In particular, these behaviors were associated with slower processing speed and worse executive function but not with verbal memory. Participants with the least active patterns of behavior (i.e., both low physical activity and high television viewing time) were the most likely to have poor cognitive function. ... Individuals with both low physical activity and high sedentary behavior may represent a critical target group," the study concludes.