SAN FRANCISCO, Dec. 3 (UPI) -- They say watching too much television will rot your brain. A new study suggests that could be true.
Researchers at the University of California San Francisco found in a long-term study, published in the Journal of the American Medical Association, that watching three hours or more of television a day in early adulthood was linked to worse cognitive function in midlife. And people who got less exercise, on top of watching a lot of television, did even worse in cognitive tests, the researchers reported.
Physical activity is important for maintaining cognitive function and brain health, so researchers were not completely surprised by the study's results.
The increasing popularity of binge watching entire television series or groups of movies has researchers wondering about results of all that screen time on 25-year-old brains in a couple of decades.
"The question is, what does it mean if you're 50, and you've got these slight changes?" Dr. Kristine Yaffe, a psychiatrist at the University of California San Francisco and lead author of the study, told NPR. "Does it mean you're on a path to greater changes down the line or does not make a difference? I don't think we really know the answer to that."
Researchers analyzed data conducted from 3,247 adults who joined the Coronary Artery Risk Development in Young Adults study in 1985 when they were between the ages of 18 and 30. The mean age of participants was 25.1, 56.5 percent were female, 54.5 percent were white, and 92.9 percent had at least a high school education. Each participant was assessed more than three times between the start of the study and 2011, when it ended.
Using the Digit Symbol Substitution Test, Stroop test and Rey Auditory Verbal Learning Test, the researchers found people watching three or more hours of television per day -- 10.9 percent of participants -- was associated with decreased cognitive performance. The 16.3 percent of participants with low physical activity also had lower scores on tests.
The combination of low physical activity and lots of television, which applied to 3.3 percent of participants, doubled the chances for people to show poor cognitive function on the tests.
Whether television is the cause or effect of having lower cognitive function is unknown, some researchers pointed out, as researchers did not measure function for participants at the beginning of the study, and the effects of sedentary behaviors on health are far from being understood.
Some television and activities that involve screens -- the study does not consider the use of tablets and smartphones because of its timeframe -- could actually be beneficial, but the researchers said they're unsure.
"There are so many more opportunities for sitting now that it's even more of a concern," Tina Hoang, a researcher at the Veterans Affairs Medical Center in San Francisco, told USA Today. "There hasn't been a lot of research showing what these early cognitive changes mean."