WASHINGTON (CNS) — In more than a dozen years of writing about television in this space, the focus has often been critiquing the aesthetic and moral quality of the content. Lately, though, the critique has been about the sheer volume of TV content consumed by viewers.

Now there is more evidence that watching a lot of TV — the couch-potato syndrome — not only does a number on your body, but also on your brain.

In a 25-year study conducted by researchers working in California, Maryland and Minnesota, the evidence points to reduced functioning because of the brain’s inability to complete tasks as a result of too much TV.

“Effect of Early Adult Patterns of Physical Activity and Television Viewing on Midlife Cognitive Function” followed 3,247 people, roughly split between men and women, a little over half white with the remainder mostly African-American, with 93 percent having finished high school, so it’s not like they were dummies at the start of the study. In truth, they were relatively fresh out of high school — ages 18-30 at the start of the study, with a median age just over 25.

The participants lived in the metropolitan areas of Chicago, Minneapolis, Oakland, California, and Birmingham, Alabama, at the start of the study. They were queried every five years as to their TV viewing habits as well as their physical activity.

Of the 3,247 subjects, 353 of them, or not quite 11 percent, admitted on at least two-thirds of the questionnaires sent over the 25-year span to not just getting in a lot of physical activity, but also to watching TV at least three hours a day. Three hours was judged by the researchers as a high level of TV watching; given that TV is on nearly twice as long each day in the average American home, three hours a day doesn’t seem so bad by comparison.

However, when you see the results, as published in the December issue of JAMA Psychiatry, the effects don’t look so good.

“High television viewing and low physical activity in early adulthood were associated with worse midlife executive function and processing speed,” the study said. “This is one of the first studies to demonstrate that these risk behaviors may be critical targets for prevention of cognitive aging even before middle age.”

Probably a lot of people who are age 43 would not consider themselves in “middle age,” but if the lack of cognitive function is permanent — given that half of the study participants have been watching a lot of the tube and not moving around much for at least half their lives — that could be a truly sobering thing.

“Sedentary behaviors and physical inactivity are not only increasing worldwide but also are critical risk factors for adverse health outcomes,” the study said.

What do the study authors mean by “executive function”? It’s not running a business like a CEO or even a vice president. In short, it means setting goals and having the mental wherewithal to achieve them. Those goals could be as simple as filling up your pants pockets with everything you need before going out of the house in the morning.

The study subjects took three different tests that measure executive function and processing speed, which is the ability to making sense of cognitive tasks, and being able to carry them out. For example, you might see a brainteaser-type magazine feature showing you a number of objects that look remarkably alike but asking you to select the one object that is unlike the others.

The researchers found that, even after adjusting for age, race, sex, education level, smoking, alcohol use, body-mass index, hypertension and other variables, “compared with participants with low television viewing and high physical activity, the odds of poor performance were almost two times higher for adults with both high television viewing and low physical activity.”

It is true that TV is not the only culprit in this study. It needs a co-conspirator, and low physical activity has been indicted by the researchers. And, when you come to think of it, how many of us just collapse in front of the tube and do nothing or next to nothing when watching TV?

Perhaps the iconic public-service TV ad urging viewer to reject drugs will have to be changed to reflect the study’s findings: “This is your brain. … This is your brain on television.”

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Pattison is media editor for Catholic News Service.