Excessive screen time may worsen sleep quality and, in turn, increase the risk of depression—especially among teenage girls, according to a new study by researchers at Sweden's Karolinska Institutet.

Published in PLOS Global Public Health, the year-long study followed 4,810 Swedish students aged 12–16, analysing their screen usage, sleep patterns, and mental health.

The researchers found that increased screen time led to poorer sleep within three months, impacting both the duration and quality of rest. It also pushed bedtimes later, disrupting several aspects of the natural sleep-wake cycle.

Crucially, the study discovered gender differences in how screen time affects mental health. For boys, screen time directly increased the risk of depression after 12 months. In contrast, for girls, depression was indirectly triggered by screen-related sleep disturbances.

“Screen-sleep displacements impact several aspects of sleep simultaneously. Displacements led to elevated depressive symptoms among girls but not boys,” the authors wrote.

Sleep was found to explain between 38% to 57% of the connection between screen use and depressive symptoms in girls. While boys also experienced disrupted sleep, the link to depression was less pronounced. “Boys may be more prone to externalising symptoms due to sleep loss,” the study noted.

This research comes months after the Swedish Public Health Agency, in September 2024, recommended that teens limit daily leisure screen time to two to three hours—partly to encourage better sleep habits.

The findings underscore the importance of healthy digital habits and suggest that national screen time guidelines may help protect adolescent mental health. The authors concluded that the results could “mirror potentially beneficial public health effects of national screen time recommendations.”