Study: too much TV, too little exercise might dull young adult brains

Young adults who watch a lot of TV and engage in very little exercise are risking more than their waist lines. By middle age, their brains may be getting out of shape too, a new study suggests.

The study, published Wednesday in the journal JAMA Psychiatry, followed more than 3,000 people, starting at an average age of 25 and ending when they took cognitive tests 25 years later.

Those who watched the most TV and got the least physical activity were the most likely to get low scores on some of the thinking tests – something that researchers say is worrisome at a time when young adults may be spending more and more hours sitting and looking at screens. TV time has been shown in other studies to be a good marker of overall inactivity.

"There are so many more opportunities for sitting now that it's even more of a concern," than when the study started, in the 1980s, said Tina Hoang, a researcher at the Veterans Affairs Medical Center, San Francisco. She was a co-author on the study led by Kristine Yaffe of the University of California, San Francisco.

During the study, participants filled out multiple questionnaires about their TV habits and physical activity — everything from walking to housework, gardening and physical labor. At the end of the study, those who reported little activity and more than three hours of daily TV time were twice as likely as their peers to score well below average on two thinking tests. The tests measured thinking speed and executive functioning —  the ability to plan and complete tasks.

Because of its design, a study like this can't prove that inactivity caused the thinking problems. But many other studies, mostly in older adults and children, suggest physical activity can improve thinking skills. The new study adds good evidence that younger adults could benefit too, said Arthur Kramer, a psychologist and neuroscientist at the University of Illinois.

Kramer and other researchers have shown that exercise improves brain cell connections and has other direct brain benefits. It also likely helps the brain by helping the heart and increasing blood flow.

Some studies even suggest exercise might help prevent or slow Alzheimer's disease. But it's too soon to say whether the relatively young couch potatoes in the new study are at any heightened risk for dementia, Hoang said.

"There hasn't been a lot of research showing what these early cognitive changes mean," she said.

The thinking problems found in the study are not the kind generally linked with Alzheimer's, said Ronald Petersen, director of the Mayo Clinic Alzheimer's Disease Research Center in Rochester, Minn. He notes that inactive participants did not score low on verbal memory tests. He said the deficits some did show might be signs of normal brain aging – hitting TV addicts earlier than their more active peers.

The good news, he said, is that the study suggests "you could do something about that," by stepping away from the TV and getting more exercise.

If the study were started today, it would have to include all the time young adults spend with screens other than TVs, Huang said. It's possible, she says, that sitting to engage in a mentally challenging video game (or to read a book) might not be as bad for the brain as sitting to passively watch TV.