Effectiveness of complex multiple-risk lifestyle interventions in reducing symptoms of depression: a study protocol for a systematic review and meta-analysis of randomised controlled trials

Introduction Many studies have explored the impact of lifestyle interventions on depression. However, little is known about the effectiveness of complex multiple-risk lifestyle interventions in reducing symptoms of depression. Our objective is to assess the effectiveness of complex multiple-risk lifestyle interventions in reducing depressive symptoms in the adult population by the acquisition of at least two healthy habits—healthy diet, physical activity and/or smoking cessation. For such purpose, a systematic review and meta-analysis of randomised controlled trials will be conducted. Method and analysis MEDLINE (through Ovid and PubMed), Scopus, Cochrane Central Register of Controlled Trials, Web of Science, PsycINFO, OpenGrey Register (System for Information on Grey Literaturein Europe) and the International Clinical Trials Registry Platform will be searched for relevant articles. Additionally, a supplementary manual search will be performed using lists of references, references to expert authors and other systematic reviews and/or meta-analyses. Study selection, data extraction (target habits, country, target populations, conditions and statistical data to name a few) and assessment of the risk of bias will be performed separately by two independent researchers. The primary outcome measure will be the reduction of depression symptoms, as measured by validated instruments. We will calculate pooled standardised mean differences and 95% CIs using random-effect models. Heterogeneity, sensitivity and publication biaswill be assessed, and sub- group analysiswill be performed. Heterogeneity will be explored by random-effects meta-regressionanalysis. Ethics and dissemination Ethical approval is not required for this study. The results of this systematic review and meta-analysis will be presented in relevant conferences and published in a peer-review journal. The findings of this study could have important clinical and scientific implications for the improvement of symptoms of depression. PROSPEROregistration number CRD42018100253; Pre-results.