Increased time spent in front of computers, mobile phones and tablets may have contributed to a surge in symptoms of depression and suicidal thoughts and behaviours in young Americans, especially girls, according to a new study.

"These increases in mental health issues among teens are very alarming," said Jean Twenge from San Diego State University. "Teens are telling us they are struggling, and we need to take that very seriously."

The results suggest that parents should be more aware of how much time their children are spending in front of screens.

For the study, Twenge and his colleagues analysed survey data from two anonymous, nationally representative surveys involving more than 500,000 US teens. They also used suicide statistics kept by the US Centers for Disease Control and Prevention.

They found that the suicide rates for girls aged between 13 and 18 increased by 65% between 2010 and 2015, while the number of girls experiencing so-called suicide-related outcomes – feeling hopeless, thinking about suicide or attempting suicide – rose by 12%. In addition, the number of teen girls reporting symptoms of severe depression rose by 58%.

"When I first saw these sudden increases in mental health issues, I wasn't sure what was causing them," said Twenge. "But these same surveys ask teens how they spend their leisure time, and between 2010 and 2015, teens increasingly spent more time with screens and less time on other activities. That was by far the largest change in their lives during this five-year period, and it's not a good formula for mental health."

The findings, published in the journal Clinical Psychological Science, showed that 48% of teens who spent five or more hours per day on electronic devices reported at least one suicide-related outcome, compared to only 28% of those who spent less than an hour a day on devices. Symptoms of depression were also more common in teens who spent large amounts of time on their devices.

Some previous research in this area has also found a link between spending more time on social media and unhappiness.

"Although we can't say for sure that the growing use of smartphones caused the increase in mental health issues, that was by far the biggest change in teens' lives between 2010 and 2015," she said.

On the other hand, the researchers did find that limiting screen-time, engaging in face-to-face social interactions and playing sports or exercising was linked to having fewer depressive symptoms and suicide-related outcomes.