Midlife heavy television viewing linked to smaller brain volumes decades later

Adults who reported watching television “very often” during midlife later showed smaller brain volumes in regions involved in memory, executive function and visual processing, along with greater white matter damage, according to a study of approximately 1,700 participants published in Alzheimer’s & Dementia (doi.org/10.1002/alz.71582).

Researchers led by the University of Southern California analyzed data from the long-running Atherosclerosis Risk in Communities (ARIC) study. Participants, who had an average age of 53 and were free of dementia at baseline, enrolled between 1987 and 1989. They self-reported the frequency of leisure-time television viewing on a scale from “never/seldom” to “very often,” as well as the proportion of their workday spent sitting. More than two decades later, between 2011 and 2013, they underwent 3T brain MRI scans measuring cortical, subcortical and Alzheimer’s disease–signature region volumes plus white matter hyperintensity (WMH) volume, as detailed in the USC Dornsife release (dornsife.usc.edu).

Compared with those who watched television never or seldom, frequent viewers exhibited reduced volumes in frontal and occipital lobes and in Alzheimer’s disease–signature regions associated with early disease changes. They also had higher WMH volumes, which indicate cerebral small vessel disease and are linked to cognitive decline, stroke risk and dementia. These associations held after adjustment for physical activity, diabetes, body mass index, smoking and alcohol use, according to the journal abstract and ScienceDaily summary of the findings (sciencedaily.com).

Notably, sitting itself did not drive the adverse patterns. Participants who reported high amounts of occupational sitting—typically more cognitively demanding desk work—showed larger frontal and occipital volumes and lower WMH volumes, patterns consistent with better brain health. “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,” said senior author David Raichlen, professor of biological sciences and anthropology at USC Dornsife, in the university’s announcement (dornsife.usc.edu).

Corresponding author Natan Feter, a postdoctoral scholar at USC, noted that health guidance may eventually need to distinguish types of sedentary behavior rather than focusing solely on total sitting time. Sex-stratified analyses indicated that most of the structural associations, both adverse for television and protective for occupational sitting, were more pronounced in men.

The study has limitations. Television habits were self-reported rather than objectively measured, and no baseline MRI was available, so the analyses could not directly track change over time within individuals. The authors call for future longitudinal imaging studies to confirm trajectories. Funding came from National Institutes of Health grants and Arizona sources. The work adds to earlier research on sedentary behavior and brain aging while highlighting that passive versus mentally active sitting may have distinct long-term associations with brain structure.