title: Association between BDNF levels and suicidal behaviour: a systematic review and meta-analysis.
abstract: BACKGROUND
  Suicidal behaviour is a complex phenomenon with a multitude of risk factors. Brain-derived neurotrophic factor (BDNF), a protein crucial to nervous system function, may be involved in suicide risk. The objective of this systematic review is to evaluate and summarize the literature examining the relationship between BDNF levels and suicidal behaviour.
  
  
  METHODS
  A predefined search strategy was used to search MEDLINE, EMBASE, PsychINFO, and CINAHL from inception to December 2015. Studies were included if they investigated the association between BDNF levels and suicidal behaviours (including completed suicide, attempted suicide, or suicidal ideation) by comparing BDNF levels in groups with and without suicidal behaviour. Only the following observational studies were included: case-control and cohort studies. Both clinical- and community-based samples were included. Screening, data extraction, and risk of bias assessment were conducted in duplicate.
  
  
  RESULTS
  Six-hundred thirty-one articles were screened, and 14 were included in the review. Three studies that assessed serum BDNF levels in individuals with suicide attempts and controls were combined in a meta-analysis that showed no significant association between serum BDNF and suicide attempts. The remaining 11 studies were not eligible for the meta-analysis and provided inconsistent findings regarding associations between BDNF and suicidal behaviour.
  
  
  CONCLUSIONS
  The findings of the meta-analysis indicate that there is no significant association between serum BDNF and attempted suicide. The qualitative review of the literature did not provide consistent support for an association between BDNF levels and suicidal behaviour. The evidence has significant methodological limitations.
  
  
  BACKGROUND
  PROSPERO CRD42015015871.
authors.affiliation: MiNDS Neuroscience Graduate Program, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L8, Canada. eisenrb@mcmaster.ca.
authors.forename: Rebecca B
authors.initials: RB
authors.lastname: Eisen
authors.affiliation: Health Research Methodology Graduate Program, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L8, Canada. pererasm@mcmaster.ca.|Department of Clinical Epidemiology and Biostatistics, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L8, Canada. pererasm@mcmaster.ca.
authors.forename: Stefan
authors.initials: S
authors.lastname: Perera
authors.affiliation: Health Sciences Library, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L8, Canada. banfie@mcmaster.ca.
authors.forename: Laura
authors.initials: L
authors.lastname: Banfield
authors.affiliation: Department of Psychiatry and Behavioural Neurosciences, McMaster University, 1280 Main St. West, Hamilton, ON, L8S 4L8, Canada. anglinr@mcmaster.ca.|Department of Medicine, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L8, Canada. anglinr@mcmaster.ca.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Anglin
authors.affiliation: Department of Psychiatry and Behavioural Neurosciences, McMaster University, 1280 Main St. West, Hamilton, ON, L8S 4L8, Canada. minuzzi@mcmaster.ca.|Women's Health Concerns Clinic, St. Joseph's Healthcare Hamilton, 50 Charlton Avenue East, Hamilton, ON, L8N 4A6, Canada. minuzzi@mcmaster.ca.
authors.forename: Luciano
authors.initials: L
authors.lastname: Minuzzi
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L8, Canada. samaanz@mcmaster.ca.|Department of Psychiatry and Behavioural Neurosciences, McMaster University, 1280 Main St. West, Hamilton, ON, L8S 4L8, Canada. samaanz@mcmaster.ca.|Population Genomics Program, Chanchlani Research Centre, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L8, Canada. samaanz@mcmaster.ca.|Peter Boris Centre for Addiction Research, St. Joseph's Healthcare Hamilton, 100 West 5th Street, Hamilton, ON, L8P 3R2, Canada. samaanz@mcmaster.ca.
authors.forename: Zainab
authors.initials: Z
authors.lastname: Samaan
mesh_terms: D015415:Biomarkers / Q000097:blood; D019208:Brain-Derived Neurotrophic Factor / Q000097:blood*; D006801:Humans; D001523:Mental Disorders / Q000097:blood* / Q000523:psychology; D064887:Observational Studies as Topic; D012307:Risk Factors; D059020:Suicidal Ideation; D013406:Suicide, Attempted / Q000523:psychology
chemical_list: D015415:Biomarkers; D019208:Brain-Derived Neurotrophic Factor; C579455:BDNF protein, human