Researchers followed 3,274 people whose average age was 25 at the start of the study for 25 years, using questionnaires every five years to collect data on their physical activity and TV watching habits. At year 25, they administered three tests that measured various aspects of mental acuity.
The highest level of TV watching — more than three hours a day most days — was associated with poor performance on all three tests. Compared with those who watched TV the least, those who watched the most had between one-and-a-half and two times the odds of poor performance on the tests, even after adjusting for age, sex, race, educational level, body mass index, smoking, alcohol use, hypertension and diabetes. Those with the lowest levels of physical activity and the highest levels of TV watching were the most likely to have poor test results.The authors acknowledge that their findings, published in JAMA Psychiatry, depend on self-reports, and that they had no baseline tests of cognitive function for comparison.“We can’t separate out what is going on with the TV watching,” said the lead author, Dr. Kristine Yaffe, a professor of psychiatry and neurology at the University of California, San Francisco. “Is it just the inactivity, or is there something about watching TV that’s the opposite of cognitive stimulation?”