title: Systematic review of environmental risk factors for Obsessive-Compulsive Disorder: A proposed roadmap from association to causation.
abstract: To synthesize the current knowledge on possible environmental risk factors for Obsessive-Compulsive Disorder (OCD).
  
  
  
  We conducted a systematic review following PRISMA guidelines. The Embase, PubMed and Scopus databases were searched up until October 6, 2015, employing relevant keywords and MeSH terms.
  
  
  
  128 studies met inclusion criteria. Potential environmental risk factors for OCD have been identified in the broad areas of perinatal complications, reproductive cycle, and stressful life events. There is limited evidence regarding other potential risk factors, such as parental age, season of birth, socioeconomic status, parental rearing practices, infections, traumatic brain injury, substance use or vitamin deficiency. In general, studies were of limited methodological quality.
  
  
  
  At present, no environmental risk factors have convincingly been associated with OCD. We propose a roadmap for future studies, consisting of longitudinal, population-based research, employing quasi-experimental family and twin designs to identify risk factors that are not only associated with the disorder but also contribute to its causation either directly or moderating the effect of genes.
authors.affiliation: Centre for Psychiatry Research, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. Electronic address: gustaf.brander@ki.se.
authors.forename: Gustaf
authors.initials: G
authors.lastname: Brander
authors.affiliation: Centre for Psychiatry Research, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Ana
authors.initials: A
authors.lastname: Pérez-Vigil
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Larsson
authors.affiliation: Centre for Psychiatry Research, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden; Stockholm Health Care Services, Stockholm County Council, Stockholm, Sweden.
authors.forename: David
authors.initials: D
authors.lastname: Mataix-Cols
mesh_terms: D006801:Humans; D008016:Life Change Events; D009771:Obsessive-Compulsive Disorder; D012098:Reproduction; D012307:Risk Factors; D019966:Substance-Related Disorders
keywords: Adoption; Environment; Famine; Genes; Immigration; Infection; Obsessive-Compulsive disorder; PANDAS; Perinatal complications; Reproductive cycle events; Risk factors; Socioeconomic status; Stressful life events; Substance abuse; Traumatic brain injury; Urbanization; Vitamin deficiency