When I kick back to watch a show, I tell myself I'm just going to watch one episode. But 45 minutes later, I'm watching another. And then another. For the rest of the day. There are a lot of things that TV and chilling can lead to, but among the less fun? Maybe more cognitive decline over time.
Researchers at the University of California, San Francisco checked in with 3,247 people for 25 years, starting when they were young adults. Every five years, they asked participants to estimate how much TV they watched daily. Every two to five years, the researchers looked at how much physical exercise people got. At the end of the 25 years, when the participants were in their 40s and 50s, they all took three tests that measured their memory, focus, and mental and physical quickness.
People who got little exercise or watched at least three hours of TV a day did worse on tests measuring cognitive focus and speed than those who got more exercise or watched less TV, according to the study, published in JAMA Psychiatry on Wednesday.
"Then people who had both low physical activity and high TV had even worse performance. It was an even bigger effect," says Dr. Kristine Yaffe, a psychiatrist at UCSF and senior author on the study.
Some of that loss of brain power could be because just sitting around motionless isn't very good for us. Scientists have known that lack of physical exercise could be a big risk factor in cognitive decline, says Marcus Richards, a psychologist at the University College London who was not involved in the study. "But we don't know much about sedentary behavior [and cognition] right now," he says. If people who spend a lot of time binge-watching TV are doing so half-comatose on a cushion, they might not be doing their brain any favors.