Adolescents suffer from depression more often than you might think: The National Institutes of Health estimates that just under 13% of all U.S. teens — over three million kids — had a at least one depressive episode in the last year.

Antidepressant medications and therapy can be very effective, and a new study suggests that a far simpler method, actively recalling happy memories from childhood, can help some teens at risk for depression.

Since people who develop depression early in life are at higher risk for having it later, it’s particularly important to find ways to nurture resilience and well-being in children and teens.

The researchers studied 425 adolescents, whose average age was 14 when the study began, conducting interviews and blood tests. Some of the teens had experienced recognizable risk factors for depression such as illness, their parents' separation or divorce, parental death or other adverse family circumstances earlier in their lives. Participants were asked about their early life events as well as any potential symptoms of depression in the previous two weeks. Their levels of the stress hormone, cortisol, were tested at the beginning of the study and after one year.

To look at the effects of recalling childhood memories on depression risk, the team had the participants take an autobiographical memory test, in which they were prompted with a word that was either positive or negative, and asked to recall memories from their childhood that were related to that word.

Teens who better remembered specific positive memories were less likely to have depression symptoms 12 months later. They also had lower cortisol levels. This was the case only among participants who had experienced negative life events. The association didn’t exist for those who hadn’t had negative life events. Being able to easily recall happier times seems to have helped protect them from much of the potentially depressing consequences of early life events.

The researchers, from the University of Cambridge and University College London, argue that by extension, encouraging kids to recall positive events from their youths may help protect them from depression.

“Our work suggests that ‘remembering the good times’ may help build resilience to stress and reduce vulnerability to depression in young people,” says Adrian Dahl Askelund, the study's lead author. “This is important as we already know that it is possible to train people to recall specific positive memories. This could be a beneficial way of helping support those young people at risk of depression.”

Depression is different from the moodiness that many teens exhibit. Depressed people have a harder time coming up with specific memories from childhood compared to non-depressed people, the authors point out; and, in fact, memory problems can be a symptom of depression. Both these factors should be taken into account when considering the results of the current study.

Still, the idea that encouraging positive memories in young people may help them develop the resilience seems to be supported by cognitive behavior therapy, in which a person is trained to replace over time negative thoughts and self-talk with more positive ones.

Depression is now the leading cause of disability worldwide, so anything that could potentially reduce a person’s risk is a good thing. And since people who develop depression early in life are at higher risk of having it later in life, it’s particularly important to find ways to nurture resilience and well-being in children and teens. Encouraging them to pay attention to their positive experiences could help.

“Mental health disorders that first occur in adolescence are more severe and more likely to recur in later life,” said study author Anne-Laura van Harmelen. “With child and adult mental health services underfunded and overstretched, it is critical that we identify new ways to build resilience, particularly in those adolescents who are most at risk for depression.”

The study is published in the journal Nature Human Behaviour.