Recently, the Swedish Public Health Agency published recommendations that adolescents use no more than two-to-three hours of daily leisure screen time, partly to promote better sleep. Previous studies have suggested associations between screen time, sleep disruptions, and depression in teens. However, sleep problems and depression often coincide, and the direction of these associations has been unclear.

In the new study, researchers tracked 4,810 Swedish students aged 12-16, collecting data on sleep quality and quantity, depressive symptoms, and screen usage at three timepoints over the course of a year.

The researchers found that increased screen time led to deteriorated sleep within three months, impacting both the duration and quality of sleep. Screen time was also found to postpone sleep times towards later hours — disrupting multiple aspects of the human sleep-wake cycle at once. Among boys, screen time had a direct adverse effect on depression after twelve months, while among girls the depressive effect was mediated through sleep disturbances. Sleep could explain about half (38%-57%) of the association between screen time and depression in girls. Boys who spent more time on screens also experienced sleep disruptions, but these were not strongly associated to later depression.

The authors summarize: “In this study, we found that adolescents who reported longer screen times also developed poorer sleep habits over time. In turn, this led to increased depression levels, especially among girls.”

They add: “Our results do suggest that less[…] screen time seems healthier, in line with previous World Health Organization statements…if screen times were somehow reduced, for example through public health policies, our results imply that the high burden of depressive states among young Swedish women, and maybe young men, would likely decrease.”