A new study suggests that young adults who watch a lot of TV and exercise little may be at risk of damaging their cognitive ability later on in life, USA Today reports.

The study was published Wednesday in the journal JAMA Psychiatry.

The study followed more than 3,000 people, when the participants were about 25 years of age and ended when they took cognitive tests 25 years later.

"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.

Tina was a co-author on the study led by Kristine Yaffe of the University of California, San Francisco.

The results of the study showed that those participants who watched the most TV and got the least physical activity were the most likely to get low scores on some of the cognitive tests. The participants 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.

Earlier studies have proved that physical activity in children and older adults can improve thinking skills. The new study shows that 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.

However, 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.

The study did not conclude that 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.

However, 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.