"Turn off that TV, it'll rot your brain!" has been repeated in households for generations. The word "rot" is clearly an exaggeration, but new research suggests that heavy television viewing may still have meaningful consequences for brain health.

A recent study published in Alzheimer's and Dementia: Journal of the Alzheimer's Association found that adults who said they watched television "very often" during midlife later showed smaller volumes in brain regions tied to memory. They also had reduced frontal and occipital lobe volume and more damage in the brain's white matter, changes that have been associated with aging, stroke risk, cognitive decline and dementia.

"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," says David Raichlen, professor of biological sciences and anthropology at the USC Dornsife College of Letters, Arts and Sciences and a senior author of the study.

Importantly, the results did not appear to be explained by inactivity alone. Other sedentary behaviors were not linked to the same brain patterns, suggesting that the type of activity a person does while sitting may be more important than researchers once assumed.

Tracking TV Habits in Midlife

The research team examined information from about 1,700 adults with an average age of 53. The participants joined the Atherosclerosis Risk in Communities (ARIC) Study between 1987 and 1989. ARIC is a long-term U.S. population study focused on cardiovascular and brain health.

Participants reported how often they watched television during their free time using a scale that ranged from "never/seldom" to "very often." They were also asked how much of their workday they spent sitting.

More than 20 years later, the participants received brain MRI scans. Compared with people who said they watched television "never" or "seldom," those who reported watching it "very often" showed broad structural differences throughout the brain.

Smaller Brain Regions and More White Matter Damage

Frequent television viewers had smaller volumes in areas connected with early signs of Alzheimer's disease. They also showed greater volumes of white matter hyperintensities, which are signs of cerebral small blood vessel disease and have been linked to cognitive decline and dementia.

The same group also had smaller frontal and occipital lobes. The frontal lobes play an important role in planning, decision-making, and other executive functions, while the occipital lobes are central to visual processing.

These differences remained even after the researchers accounted for physical activity, diabetes, body mass index, smoking, and alcohol use.

The study did have important limitations. Television habits were self-reported, which is generally less precise than directly measuring viewing time. Participants also did not receive MRI scans at the beginning of the study. Future work that includes baseline imaging could provide stronger evidence of how brain structure changes over time.

Why All Sitting May Not Be Equal

One of the most surprising findings was that sitting itself did not seem to be the primary factor behind the observed brain differences.

Participants who spent a large portion of their workday sitting actually had larger frontal and occipital lobes and lower white matter hyperintensity volumes. Those patterns suggest better brain health than what was observed among people who spent their sitting time watching television.

The study authors say one possible explanation is that many seated jobs involve problem-solving, concentration and other forms of intellectual stimulation. In other words, mentally active sitting may affect the brain differently from passive television viewing.

Brain Changes Were More Pronounced in Men

The researchers also found differences between men and women. When they examined the MRI data by sex, most of the brain changes associated with television viewing and sitting at work appeared in men.

That result suggests men may be especially vulnerable to the brain effects linked with these behaviors, although more research will be needed to understand why.

The findings highlight the complexity of sedentary behavior and suggest that future health recommendations may need to become more specific. Instead of only telling patients to sit less, physicians may eventually encourage them to limit television time and choose more mentally engaging activities when they are seated.

"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," says study corresponding author Natan Feter, postdoctoral scholar in the Human and Evolutionary Biology program at USC Dornsife.

About This Study

In addition to Raichlen and Feter, study authors include Anamika Nanda, Mark Lai, Rand Wilcox and Sarah Hourihan of USC Dornsife; Daniel Aslan of Harvard University; Jayne Feter of Universidade Federal do Rio Grande do Sul; M. Katherine Sayre of University of California, Santa Barbara; Pradyumna Bharadwaj, Madeline Ally, Hyun Son, Yann Klimentidis, Amit Arora and Gene Alexander of the University of Arizona; Silvio Maltagliati of USC Dornsife and Université Bretagne Sud.

This research was supported by National Institutes of Health grants P30AG072980, P30AG019610, R56AG067200, R01AG064587, and R01AG072445 and funding from the state of Arizona, the Arizona Department of Health Services, and the McKnight Brain Research Foundation.