Subthreshold depression in adolescents can be successfully treated with psychological interventions, study finds

Characterized by clinically relevant symptoms that do not meet criteria for a depressive disorder, subthreshold depression can still have functionally impairing effects, leading to an increased risk of experiencing a major depression event and personal suffering.

Lead author, Pim Cuijpers, Professor of Clinical Psychology, Vrije Universiteit Amsterdam in the Netherlands said: "It has become increasingly clear that depression can be best viewed asa continuum-ranging from no depression at all, to very severe at the other end-and many different states in between. Because the prevalence can be seen as much higher than the frequency of major depression, subthreshold depression is associated with a considerable disease burden on the population level and has also been found to be associated with the development of major depression and other mental disorders."

While there have been several randomized trials examining the effects of psychological interventions on subthreshold depression in children and adolescents, these studies have not all resulted in the same outcomes.

To connect the dots between the existing research, the authors conducted an extensive search of bibliographic databases, and identified 12 studies examining psychological interventions for subthreshold depression in children and adolescents. With a total of 1,576 participants, these earlier outcomes were compared with usual care or other control conditions. Some studies also provided longer follow-up measurements to examine how many participants developed a depressive disorder over time.

The authors found that most studies focused on adolescents and only two examined children below 12 years of age, which meant there was not enough data to provide evidence on the effects of subthreshold depression in children.

For adolescents however, a significant effect was found for the psychological interventions. The effect size was moderate (with a standardized mean difference of 0.38), indicating that approximately eight adolescents had to be treated in order to have one more positive outcome than no treatment at all. When studies with low quality were excluded very comparable effects were found.

The overall findings also uncovered some indications for "publication bias," a phenomenon that results in negative studies being overlooked (or not published at all), as they do not promote results that show a significant finding. After statistical adjustment for this type of bias, the effects were considerably smaller (standardized mean difference of 0.24).

No significant effect was found on the incidence of new cases of major depression at follow-up. Although the results pointed in the expected direction (the risk to develop a depressive disorder was reduced to approximately 50% in the treatments) this was not significant. This finding could be related to the small number of studies examining this outcome.

Overall, this study shows that interventions for subthreshold depression may have positive effects in adolescents. At this point in time however, there is insufficient evidence that these interventions are effective in children less than 12 years of age, or that they prevent the onset of major depression at follow-up.