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Researchers found that people who reported watching television more often in midlife had smaller brain volumes decades later in areas involved in language and thinking. On the other hand, sitting at work was linked to healthier brain measures.

What should people make of these findings? Does this mean it’s time to turn off the television for good? To help answer these questions, I spoke with CNN wellness expert Dr. Leana Wen, an emergency physician and clinical associate professor at George Washington University. She previously served as Baltimore’s health commissioner.

CNN: Is watching television really associated with changes in the brain years later?

Dr. Leana Wen: That’s what this study found, although it’s important to understand exactly what the researchers measured and what conclusions we can draw from it.

Investigators analyzed data from more than 1,700 participants in a long-running study funded by the National Institutes of Health. Middle-aged participants reported how often they watched television and how much they sat at work during the previous year. For television viewing, they self-reported in a standardized questionnaire how often they watched television by classifying their habits into one of five categories: never, seldom, sometimes, often or very often. Participants ranged from 45 to 64 at the start of the study, with an average age of 53. More than two decades later, they underwent brain MRI scans.

People who reported watching television “very often” often had smaller volumes in several brain regions, including in parts involved in cognitive control and language as well as areas that are especially vulnerable early in Alzheimer’s disease. These viewers also had more white matter hyperintensities, which are changes seen on MRI that reflect injury to the brain’s small blood vessels and have been linked to cognitive decline and dementia.

CNN: One of the most surprising findings was that sedentary activity in another context — at work — wasn’t linked to the same brain changes. Why might watching television be different from sitting at work?

Wen: This interesting finding suggests that not all sedentary activities are the same. Watching television is a cognitively passive activity because viewers are primarily receiving information rather than actively processing it. Sitting at work often involves very different mental demands. You may be responding to emails, working on projects and interacting with colleagues. Those activities engage multiple brain networks even though you’re sitting.

Watching TV is typically considered a passive sedentary activity unlike doing a puzzle or sitting at work and engaging with coworkers. Antonio_Diaz/iStockphoto/Getty Images The study doesn’t prove that mentally stimulating activities protect the brain, but the findings fit with a growing body of research suggesting that cognitive engagement helps reduce the risk of dementia. Previous studies also have found differences between passive sedentary behaviors, such as television watching, and more mentally active ones, including solving puzzles and being mentally engaged during work.

CNN: Does this study prove that watching television causes negative brain changes?

Wen: No. This was an observational study, which means it can identify associations but cannot establish cause and effect.

It also may be that subtle changes in brain health influenced people’s habits years before the MRI scans were performed such that people with brain matter changes were more likely to spend their days watching television than those participants who didn’t display the brain matter changes.

Still, this was a well-conducted study that followed participants for more than two decades and used detailed brain MRI scans rather than subjective testing. While the findings should not be interpreted as proof that television damages the brain, they add to growing evidence that prolonged passive, sedentary behavior is not ideal for long-term brain health.

Doctor consulting patient for covid vaccine, wellness check and medical test results in clinic surgery. Healthcare worker and hospital staff in discussion about medicine service and healthy feedback Jacob Wackerhausen/iStockphoto/Getty Images Your level of physical activity could be a vital sign

CNN: The researchers adjusted for physical activity. Does that mean going to the gym isn’t enough to offset hours spent watching television?

Wen: It’s an interesting point because we know that staying physically active helps to reduce the risk of dementia. But regular exercise doesn’t offset all other risk factors.

In this study, the association between heavy television viewing and brain changes remained even after the researchers accounted for physical activity. In other words, someone who exercises regularly but also spends many hours each day watching television still has additional risks for worse cognitive health because of their passive sedentary behavior. Staying physically active and limiting this kind of prolonged passive sedentary behavior both appear to be important.

CNN: Should people swear off watching TV? What about other forms of passive screen time, such as scrolling on a phone or tablet?

Wen: I don’t think this study means people should stop all screen consumption. Watching a sporting event, following a favorite show or going to a movie can be fun and relaxing, and these pastimes help us to connect with family and friends, which is good for our health on many levels.

The Good Brigade/Digital Vision/Getty Images What’s your Brain Care Score? The answer may indicate your dementia risk

In my view, the key takeaway is to think about how much time is spent in passive screen-based activities and what those activities may be replacing. If several hours of television or scrolling through social media are taking the place of exercise, in-person social interactions, reading or other mentally stimulating activities, that’s not ideal for brain health.

People should consider that not all screen time is the same. For example, participating in an online language class in which you are learning a new skill and actively communicating with others engages the brain differently than passively watching TV shows or mindlessly scrolling through internet content. And it’s always a good idea to avoid sitting for long, uninterrupted periods by getting up periodically to stretch and walk around.

Michelle Rae Uy/CNN Underscored 29 of the best gifts for trying new hobbies, according to the lifelong hobbyists on our team (Courtesy CNN Underscored)

CNN: Besides reducing passive screen time, what are evidence-based ways to protect brain health as we age?

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