The familiar warning to stop staring at the television because it will “rot your brain” may contain more truth than parents once realized, though scientists say the picture is far more complicated.
A study published in Alzheimer’s & Dementia found that people who reported watching television more frequently in middle age showed differences in brain structure more than two decades later. Researchers from the University of Southern California and other institutions analyzed data from 1,712 participants whose average age was 53 when the study began.
Between 1987 and 1989, participants reported how often they watched television and how much time they spent sitting at work. About 24 years later, between 2011 and 2013, they underwent MRI brain scans.
Importantly, the researchers did not repeatedly scan participants over the intervening decades. They therefore could not track how individual brains changed over time. Instead, they examined whether midlife viewing habits were associated with brain structure later in life.
More TV, more differences in the brain
Participants who reported the most frequent television viewing had smaller volumes in several brain regions than those who said they watched rarely or not at all. Some of the affected areas are considered vulnerable to processes associated with Alzheimer’s disease.
Frequent viewers also had a greater burden of white matter hyperintensities, or WMHs, bright areas that appear on MRI scans and are often associated with changes in the brain’s small blood vessels.
Previous research has linked WMHs to brain aging, cognitive decline and increased risk of dementia and stroke. But the researchers stressed that the new findings do not show that television caused the brain differences, nor do they mean that frequent viewers will necessarily develop Alzheimer’s disease or dementia.
Sitting at work told a different story
One of the study’s more intriguing findings was that not all sedentary behavior appeared to be associated with the same outcomes.
While frequent television viewing was linked to several less favorable measures of brain structure, participants who reported sitting frequently at work showed a different pattern. On some measures, greater occupational sitting was associated with larger brain regions and fewer white-matter abnormalities.
“For years, we have focused on how much time people spend sitting,” said Prof. David Raichlen, one of the study’s senior researchers. The findings, he said, suggest it may also matter what people are doing while they are seated.
(Photo: Shutterstock/Yuganov Konstantin)
Researcher Nathan Pater similarly suggested that future recommendations about reducing sedentary time may need to distinguish between different types of seated activity.
The researchers raised one possible explanation: desk work may often involve problem-solving, communication, decision-making and other mentally demanding tasks, while television viewing tends to be more passive.
The study did not directly test that mechanism, however, so researchers cannot say that mental stimulation is what accounts for the difference.
Men appeared more affected
The team also found differences between men and women.
When researchers analyzed the MRI findings separately by sex, many of the associations between frequent television viewing and less favorable brain measures were more pronounced among men.
Why that occurred remains unclear. The researchers said further work is needed to determine whether biological differences, viewing habits or other unmeasured factors could explain the pattern.
The analysis attempted to account for a wide range of variables that could affect brain health, including age, education, physical activity, smoking, alcohol consumption, diabetes, high blood pressure and body mass index.
Some associations remained statistically significant even after those adjustments, but that still does not establish cause and effect.
Should you throw out the television?
Not based on this study.
There are several important limitations. Television viewing and sitting habits were self-reported, and participants were not asked to specify exactly how many hours they watched each day. Instead, they classified their viewing frequency along a scale ranging from rarely or never to very often.
That means the researchers cannot identify a specific number of viewing hours beyond which risk begins to rise.
(Photo: Shutterstock/True Touch Lifestyle)
Another major limitation is the lack of baseline MRI scans. Researchers know how participants’ brains looked about 24 years later, but they do not know whether some of the structural differences were already present at the beginning of the study.
The findings therefore show an association between television habits and later brain structure, not proof that television caused the differences.
The broader message may be that all sitting is not equal.
The study adds to a growing body of research suggesting that what people do during sedentary time may matter alongside how long they remain inactive. Time spent watching television may affect the brain differently from time spent working, reading, socializing or carrying out cognitively demanding tasks.
Replacing some passive viewing time with physical activity, social interaction or mentally challenging activities could be a reasonable choice for brain health, the researchers said. But proving that such a change can prevent structural brain changes or reduce dementia risk will require further research.