Young adults who watch tons of TV, and spend more time on the couch than at the gym, may end up paying for it with diminished mental performance in middle-age, new research suggests.
"We found that low physical activity and high TV watching in young adulthood were associated with worse cognitive [mental] function" in middle-age, said Tina Hoang, a staff research associate with the Northern California Institute for Research and Education at the Veterans Affairs Medical Center in San Francisco.
And that finding was "particularly surprising," added Hoang, given that the current study pointed to a negative impact on mental function in people who were mostly in their 50s. Seniors have been the focus of most prior investigations, she explained.
But, "this is really a preliminary study," she cautioned. Hoang also acknowledged that while TV time and physical inactivity seem to be associated with diminished mental ability, the study couldn't show whether or not such lifestyle factors actually cause mental decline. "More work is needed to really understand this relationship," she added.
The study findings were published in the Dec. 2 online edition of JAMA Psychiatry.
To gauge the long-range mental health impact of TV and physical activity habits, investigators enlisted more than 3,200 men and women. Study participants were an average of about 25 years old when the study began. Most (55 percent) were white and 57 percent were female. More than 90 percent of the study volunteers finished high school, the researchers said.
Over the 25-year study, all of the participants completed at least three detailed lifestyle questionnaires.
The study authors defined high TV-viewers as people who watched more than three hours of TV per day during the prior year (on at least two-thirds of the questionnaires they filled out).
The researchers calculated physical activity by exercise units. These units were measured using a combination of duration of exercise with intensity of exercise. Those who scored low on physical activity were below the baseline number of exercise units for their sex, the study said.
Mental capacity was assessed by testing that looked at verbal memory skills, and the ability and speed with which participants were able to plan, organize and perform mental tasks.
In the end, the investigators found that 11 percent of the study volunteers were high TV-watchers. At middle-age, high TV-watchers were more likely to fare poorly on most mental function testing compared with low TV-watchers, the study found. The one exception the researchers discovered was that high TV-watchers did not fare worse in terms of verbal memory.
Those whose physical activity levels were ranked as low (about 16 percent of participants) were significantly more likely than those ranked high to fare poorly in terms of the ability to think quickly and perform mental tasks, the study found.
And participants who were both high TV-viewers and low exercisers had up to double the risk for poor mental performance by middle-age, compared with those who had been both low TV consumers and more physically active during young adulthood, the findings showed.
Could other "couch-potato" factors apart from TV viewing -- such as poor nutrition or reading less -- decrease mental performance down the road?
"We did try to control for some confounding factors, such as education, body mass index, smoking and alcohol use," Hoang said. "But there may be others that we were not able to account for."
Susan Albers is a psychologist in the department of psychiatry and psychology with the Cleveland Clinic in Wooster, Ohio. Albers cautioned that, ultimately, "there are too many variables and confounding factors to say that the behaviors of TV watching and a sedentary lifestyle is a direct ticket to cognitive deficits."
Yet, she added, "there is no surprise that there is an association." And the findings clearly highlight that "what you do in your teens and early adulthood matters," Albers said.
"Young adults often don't make the connection between what they do now and what happens 25 years from now," she pointed out. "This study helps connect the dots."