Background: Adolescence is a peak time for the onset of depression, but little is known about what adolescents can do to reduce their own level of risk. To fill this gap, a review was carried out to identify risk and protective factors for depression during adolescence that are modifiable by the young person.

Methods: Employing the PRISMA method, we conducted a systematic review and meta-analysis of longitudinal studies to identify risk and protective factors during the adolescent period (aged 12-18 years) that are potentially modifiable by the young person without professional intervention or assistance. Stouffer׳s method of combining p values was used to determine whether associations between variables were reliable, and meta-analyses were conducted to estimate the mean effect sizes of associations.

Results: We identified 113 publications which met the inclusion criteria. Putative risk factors implicated in the development of depression for which there is a sound evidence base, and which are potentially modifiable during adolescence without professional intervention, are: substance use (alcohol, tobacco, cannabis, other illicit drugs, and polydrug use); dieting; negative coping strategies; and weight. Modifiable protective factors with a sound evidence base are healthy diet and sleep.

Limitations: Limitations include not systematically reviewing moderators and mediators, the lack of generalisability across cultures or to younger children or young adults, and the inability to conduct a meta-analysis on all included studies.

Conclusions: Findings from this review suggest that future health education campaigns or self-help prevention interventions targeting adolescent depression should aim to reduce substance use (alcohol, tobacco, cannabis, other illicit drugs, and polydrug use); dieting; and negative coping strategies; and promote healthy weight; diet; and sleep patterns.