title: Sleep and circadian alterations in people at risk for bipolar disorder: A systematic review.
abstract: Sleep and circadian abnormalities have been mostly demonstrated in bipolar patients. However, it is not clear whether these alterations are present in population at high risk for bipolar disorder (BD), indicating a possible risk factor for this condition.
  
  
  
  This systematic review aims to define current evidence about sleep and rhythm alterations in people at risk for BD and to evaluate sleep and circadian disorders as risk factor for BD.
  
  
  
  The systematic review included all articles about the topic until February 2016. Two researchers performed an electronic search of PubMed and Cochrane Library. Keywords used were 'sleep' or 'rhythm' or 'circadian' AND 'bipolar disorder' or 'mania' or 'bipolar depression' AND 'high-risk' or 'risk'.
  
  
  
  Thirty articles were analyzed (7451 participants at risk for BD). Sleep disturbances are frequent in studies using both subjective measures and actigraphy. High-risk individuals reported irregularity of sleep/wake times, poor sleep and circadian rhythm disruption. Poor sleep quality, nighttime awakenings, and inadequate sleep are possible predictive factors for BD. A unique study suggested that irregular rhythms increase risk of conversion. People at risk for BD showed high cortisol levels in different times of day. Studies about anatomopathology, melatonin levels, inflammatory cytokines and oxidative stress were not identified. The most important limitations were differences in sleep and rhythm measures, heterogeneity of study designs, and lack of consistency in the definition of population at risk.
  
  
  
  Sleep and circadian disturbances are common in people at risk for BD. However, the pathophysiology of these alterations and the impact on BD onset are still unclear.
authors.affiliation: Department of Medical Sciences, Universidade Federal do Ceará, Brazil. Electronic address: matcarv01@yahoo.com.br.
authors.forename: Matias Carvalho Aguiar
authors.initials: MC
authors.lastname: Melo
authors.affiliation: Hospital de Saúde Mental Professor Frota Pinto, Brazil.
authors.forename: Raquel Fernandes
authors.initials: RF
authors.lastname: Garcia
authors.affiliation: Hospital de Saúde Mental Professor Frota Pinto, Brazil.
authors.forename: Vicente Bezerra
authors.initials: VB
authors.lastname: Linhares Neto
authors.affiliation: Hospital de Saúde Mental Professor Frota Pinto, Brazil.
authors.forename: Mariana Brasil
authors.initials: MB
authors.lastname: Sá
authors.affiliation: Hospital de Saúde Mental Professor Frota Pinto, Brazil.
authors.forename: Licia Marah Figueredo
authors.initials: LM
authors.lastname: de Mesquita
authors.affiliation: Hospital de Saúde Mental Professor Frota Pinto, Brazil.
authors.forename: Carolina Freitas Cardeal
authors.initials: CF
authors.lastname: de Araújo
authors.affiliation: Department of Medical Sciences, Universidade Federal do Ceará, Brazil.
authors.forename: Veralice Meireles Sales
authors.initials: VM
authors.lastname: de Bruin
mesh_terms: D001714:Bipolar Disorder / Q000150:complications*; D021081:Chronobiology Disorders / Q000209:etiology*; D006801:Humans; D012307:Risk Factors; D012893:Sleep Wake Disorders / Q000209:etiology*
keywords: Bipolar disorder; Chronobiology; Circadian rhythm; Sleep