People who reported watching more than three hours of television per day as young adults were twice as likely to suffer from poor cognition down the road, compared to those who were more active and reported less screen time.
The research tracked 3,247 adults, aged 18-30 when they enrolled in the study published in the Journal of the American Medical Association (JAMA) Psychiatry.
Scientists assessed cognitive function in the 25th year using three tests of mental processing speed, executive function and verbal memory.
Low levels of physical activity and lots of television-watching were linked to slower processing speed and worse executive function, the study found.
“Participants with the least active patterns of behavior (i.e., both low physical activity and high television viewing time) were the most likely to have poor cognitive function,” said the study.
Verbal memory, however, did not appear to be affected by the amount of television time.
The study was led by Tina Hoang of the Northern California Institute for Research and Education at the Veterans Affairs Medical Center, San Francisco; and Kristine Yaffe of the University of California, San Francisco.
According to Andrew Przybylski, an experimental psychologist at the University of Oxford, who was not involved in the findings, the study contained shortcomings.
“First, these data rely entirely on a potentially problematic self-reported measure for television time,” he said in a statement.
Researchers also did not study participants’ cognitive function at the beginning of the study, in order to have a baseline for a comparison.
He also pointed out that “nearly one in three participants did not complete the study,” further weakening the strength of the findings.
“Taken together, the work should provoke continued conversation about the nature of different forms of interactive media and underline the value of open science methodology including open datasets, pre-registered analysis plans, and robust and open peer review process,” he said in a statement.
“Until these innovations are introduced into this research literature, we will be left scratching our heads at studies like this.”