Midlife TV habits tied to later brain differences in long study

Adults who reported watching television very often in midlife later showed brain differences tied to memory, decision-making and visual processing, according to researchers at the University of Southern California. The findings suggest the brain effects of sedentary time may depend on what people do while seated, not only how long they sit.

The study, published in Alzheimer's and Dementia: Journal of the Alzheimer's Association, used data from about 1,700 adults in the Atherosclerosis Risk in Communities Study, a long-running U.S. project focused on cardiovascular and brain health. Participants had an average age of 53 when they entered the study between 1987 and 1989, USC said.

TV viewing tracked before later brain scans

Researchers asked participants how often they watched television during leisure time, using answers ranging from “never/seldom” to “very often,” according to USC. Participants also reported how much of their workday they spent sitting.

More than two decades later, participants underwent brain MRI scans. USC said people who had reported watching television “very often” showed smaller volumes in brain areas connected to memory, along with smaller frontal and occipital lobes.

The frontal lobes are involved in planning, decision-making and other executive functions, while the occipital lobes support visual processing, according to the research summary from USC. Frequent television viewers also had more white matter hyperintensities, a type of MRI finding linked in prior research to small blood vessel disease in the brain, cognitive decline and dementia.

The associations remained after the researchers accounted for several health and lifestyle factors, including physical activity, diabetes, body mass index, smoking and alcohol use, USC said. The study did not prove that television viewing caused the later brain differences.

Passive sitting may differ from seated work

David Raichlen, a professor of biological sciences and anthropology at USC Dornsife and a senior author of the study, said the results point beyond total sitting time. “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,” Raichlen said.

USC said other sedentary behavior did not show the same pattern as frequent television viewing. Participants who spent much of their workday sitting had larger frontal and occipital lobes and lower volumes of white matter hyperintensities, according to the study summary.

The authors suggested that seated work may often involve concentration, problem-solving and other mental activity. That could help explain why passive television viewing and mentally demanding sitting were associated with different brain patterns, USC said.

Natan Feter, a USC Dornsife postdoctoral scholar and corresponding author, said public health advice may need to address seated activities more specifically. “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,” Feter said.

Limits and sex differences

The researchers also reported that most of the brain changes associated with television viewing and sitting at work appeared in men when the MRI results were analyzed by sex. USC said more research is needed to understand why that difference appeared.

The authors noted several limits. Television habits were self-reported, which is less precise than directly measuring viewing time, and participants did not receive MRI scans at the start of the study, USC said. Baseline scans in future studies could help researchers better measure how brain structure changes over time.

This story draws on original reporting from ScienceDaily.