Frequent TV watching in midlife was associated with smaller brain structures linked to memory and thinking decades later.
The same pattern was not seen with sitting at work, suggesting different sedentary activities may affect the brain differently.
The study found an association — not proof that television watching directly causes these brain changes.
Many of us have heard the warning that watching too much television is "bad for your brain." While that's an oversimplification, new research suggests there may be some truth behind the idea — at least when it comes to frequent TV viewing during midlife.
Researchers from the University of Southern California analyzed long-term health data and found that people who reported watching television "very often" in their leisure time during middle age were more likely to show smaller brain structures decades later.
Those changes appeared in areas involved in memory, decision-making and visual processing, as well as in regions that are known to be affected early in Alzheimer's disease. The researchers also found more white matter changes, which have been linked to aging, cognitive decline and stroke risk. Importantly, the findings show an association rather than proving that television watching directly caused these differences.
“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,” researcher David Raichlen said in a news release.
How the study was conducted
The study included 1,712 adults who participated in the long-running Atherosclerosis Risk in Communities (ARIC) study.
Participants were about 53 years old, on average, when they first answered questions between 1987 and 1989 about how often they watched television during their free time and how much of their workday they spent sitting.
More than 20 years later, participants underwent brain MRI scans. Researchers compared the scans with the earlier survey responses while accounting for several factors that could influence brain health, including physical activity, diabetes, body mass index, smoking and alcohol use.
The study relied on self-reported television habits, and participants did not receive brain scans at the beginning of the study, both of which are important limitations the authors acknowledged.
What the findings could mean
One of the most notable findings was that not all sitting appeared to have the same relationship with brain health.
While frequent television viewing was linked to smaller brain volumes and greater white matter changes, spending long periods sitting at work was associated with larger brain volumes in some regions and lower levels of white matter changes. The researchers suggest that mentally engaging work activities may differ from the more passive nature of television viewing.
The researchers also found that many of the observed brain differences were more pronounced in men, although additional research is needed to better understand why. Overall, the findings suggest that it may be worth paying attention not only to how much time people spend sitting, but also to how they spend that time.
“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 seems to have distinct impacts on brain health,” researcher Natan Feter said in the release.