(iStock)

If you've stumbled across this page after binge-watching on Netflix for the third time this week, you'd better turn off that screen and pay attention.

In a pretty alarming finding for those of us who love TV, a new study published in JAMA Psychiatry this week shows that young adults who watch a lot of television and have a low physical activity level tended to have worse cognitive function as measured by standardized tests when they hit middle age.

In the 25-year study, researchers followed 3,247 people starting at age 18 to age 30 and had them fill out questionnaires about their television viewing and physical activity during repeated check-ins at years five, 10, 15, 20 and 25 of the study. The median age of the participants, who were recruited from Birmingham, Ala., Chicago, Minneapolis and Oakland, Calif., was 25.1 years at start, with about an even split between men and women. A little over half were white, and the rest were mostly black. Nearly all the volunteers, some 93 percent, had completed at least high school.

The 353 volunteers who said they were watching more than three hours a day for more than two-thirds of the check-ins were categorized as having a "high" amount of television viewing. The others were designated as having moderate or low patterns of TV viewing.

Numerous studies over the years have shown how sedentary behaviors like watching television can hurt your body and that conclusion is now widely accepted. Now evidence is building that being a couch potato earlier in your life may impair your brain, too.

This study, which was partially funded by the National Heart, Lung, and Blood Institute, is one of the first to report an adverse association between TV watching in early adulthood and midlife cognitive issues.

Each participant was given three cognitive tests at the end of year 25 of the study. One, the Digit Symbol Substitution Test or DSST assesses processing speed and executive function. The first is a measure of how quickly a person can make sense of and carry out cognitive tasks. In IQ tests for kids, the tasks involve something like finding the bugs with specific characteristics in a row of bugs. Executive function refers to a person's ability to manage time and resources to achieve a goal. A person with poor executive function may constantly lose his keys, for instance, and have trouble getting out the door for work each morning.

The second test, the Stroop test, was also one that delved into executive function. The third, the Rey Auditory Verbal Learning Test or RAVLT, assesses verbal memory which involves the recall of words or other abstractions involving language. It's usually  assessed by asking a person to recount a list of words or a short story.

After adjusting for things like age, race, sex, education level, smoking, alcohol use, BMI and other factors, the researchers found that participants with high television viewing and low physical activity were two times as likely to perform poorly — which was defined as one standard deviation below the mean — on the first two tests.

The good news in the bad news of the study was the verbal memory did not seem to be impacted (perhaps because watching a lot of people talking on TV keeps your brain active in this regard?).

The researchers theorized that "physical activity during young adulthood may preserve cognitive function and contribute to cognitive reserve by increasing neurogenesis as well as synaptic plasticity, particularly in regions associated with executive function and processing speed."

Read more:

With $45 billion pledge to charity, Mark Zuckerberg and wife imagine ‘a world without suffering from disease’

The myth of sugar-free drinks, candy: Study shows they can wreak havoc on teeth, too

Modern men tend to overeat like cavemen as a way of showing off to women

For more health news, you can sign up for our weekly newsletter here.