The amount of time teenagers watch television increases their risk of becoming depressed as an adult, researchers find.
Researchers at the University of Pittsburgh and Harvard Medical School looked at the media habits of 4,142 healthy adolescents and calculated that each additional hour of TV watched per day boosted the odds of becoming depressed by 8%.
The results don't prove that TV viewing itself causes depression, said Dr. Brian Primack of the University of Pittsburgh's Center for Research on Health Care, who led the study. "It could be argued that people with the predilection for later development of depression also happen to have a predilection for watching lots of TV," he said.
But the circumstantial evidence pointing to TV as the culprit is strong, the study found.
The researchers examined data from the National Longitudinal Study of Adolescent Health, which followed a representative sample of American teens for seven years. When the subjects were initially surveyed in 1995, as junior high and high school students, they watched TV for an average of 2.3 hours each day. They also spent 37 minutes daily watching videocassettes, 25 minutes playing computer games and 2.3 hours listening to the radio.
In 2002, when the participants were interviewed again in their 20s, 308 of them met the criteria for depression, the study found. Teens who became depressed had watched 22 more minutes of TV each day, on average, compared with teens who did not. That dose-response relationship suggests that the boob tube was at least partly to blame, said Primack, a family practice physician.
The researchers described several possible mechanisms that could be at play. Perhaps TV watching cut into time that could have been spent on organized after-school activities and other pursuits thought to reduce the risk of depression.
TV watching also could have displaced sleep, which is important for cognitive and emotional growth.
The programs and ads teens watched may have made them feel inadequate and worthless, or they could have stirred feelings of anxiety and fear, all of which contribute to depression, researchers said.
Compared with other forms of media, TV may be particularly damaging because it is so time-consuming, all-absorbing and laden with ads. If that's true, Primack said, today's teens could be even more vulnerable.
But Andrew Campbell, who studies media use and mental health at the University of Sydney in Australia, said disturbing images were more prevalent on TV now than in the mid-1990s, and viewers of all ages were probably more inured to them. Thus, if disturbing images were causing the increased rates of depression observed in the study, the link should not be as strong today, he said.