Frequent television viewing in middle age may lead to a literal shrinking of the brain and an increased risk of dementia, according to a study conducted by researchers at the University of Southern California (USC).
The findings, published in the Alzheimer’s and Dementia: Journal of the Alzheimer’s Association, analyzed data from over 1,700 middle-aged adults participating in the Atherosclerosis Risk in Communities (ARIC) Study. Participants, with an average age of 53, reported their television viewing habits and sedentary time between 1987 and 1989.
Two decades later, these individuals underwent MRI brain scans. The results indicated that those who reported watching television "very often" exhibited significant structural differences in their brains compared to those who rarely or never watched TV. Specifically, regular viewers showed reduced brain volume in areas associated with early indicators of Alzheimer's disease.
These individuals also displayed a higher incidence of white matter hyperintensity, a marker of small blood vessel disease in the brain linked to cognitive decline and dementia. Furthermore, their occipital and frontal lobes—regions responsible for visual processing and executive functions like planning and decision-making—were smaller.
Senior study author David Raichlen of USC Dornsife College of Letters, Arts and Sciences noted, "For years we’ve focused on how much people sit. Our findings suggest we should also pay attention to what they’re doing while they’re sitting."
Interestingly, the study found that these brain changes were more pronounced in men. The research accounted for various other health and lifestyle factors, including physical activity, body mass index, smoking, and alcohol consumption. The association between increased TV viewing and brain changes persisted even when these variables were controlled.
The study differentiated between sedentary activities, suggesting that TV watching may be more detrimental than other seated tasks, such as working at an office. Participants who spent significant time sitting at work showed lower levels of white matter hyperintensity and larger frontal and occipital lobes compared to heavy TV watchers, indicating better brain health.
Researchers theorize that sedentary jobs might involve more cognitive engagement than passive TV viewing, contributing to this difference. However, the study acknowledges limitations, including the reliance on self-reported TV habits, which may be less accurate than objective monitoring. Additionally, MRI scans were not conducted at the beginning of the study, making it impossible to track individual brain changes over time.
Despite these caveats, the researchers suggest that health professionals should broaden their advice on sedentary behavior to include the specific activities performed while sitting, as these appear to have distinct impacts on brain health. Co-author Natan Feter, a postdoctoral scholar at USC Dornsife, stated, "We frequently encourage the public not to spend too much time sitting down, but experts may want to expand that recommendation to encompass the activities done while sitting, since those seem to have distinct impacts on brain health."