title: The impact of headache and chronic musculoskeletal complaints on the risk of insomnia: longitudinal data from the Nord-Trøndelag health study.
abstract: BACKGROUND
  A strong relationship between insomnia and painful disorders has been found, but it is still unclear whether chronic pain leads to insomnia. There is a need of large-scale prospective studies to evaluate if there is a causal relationship between painful disorders and insomnia.
  
  
  METHODS
  All inhabitants aged ≥ 20 years in Nord-Trøndelag County of Norway were invited to participate in two surveys (n = 92,566 and 93,860, respectively). 27,185 subjects participated in both surveys, and 19,271 of these were insomnia-free at baseline (population at risk). Using logistic regression, we evaluated the influence of headache, CMSCs and coexisting headache and CMSCs on the subsequent risk of insomnia.
  
  
  RESULTS
  Compared to subjects without headache and CMSCs, there was an increased risk of insomnia among those with headache, most pronounced among those with headache ≥ 7 days / month (OR = 2.2, 95% CI = 1.9 - 2.6). Similarly, an increased risk among those with CMSCs was found, most evident for those with widespread CMSCs (OR = 2.0, 95% CI = 1.8 - 2.2). Having coexistent CMSCs and headache (OR = 2.0, 95% CI = 1.8 - 2.2) predisposed more strongly to insomnia than having headache (OR = 1.5, 95% CI = 1.3 - 1.6) and CMSCs (OR = 1.6, 95% CI = 1.4 - 1.7) alone.
  
  
  CONCLUSIONS
  In this prospective study headache and CMSCs were risk factors for insomnia 11 years later.
authors.affiliation: Department of Neuroscience; Faculty of medicine, Norwegian University of Science and Technology, MTFS, Trondheim N-7489, Norway. sivstein@stud.ntnu.no
authors.forename: Siv Steinsmo
authors.initials: SS
authors.lastname: Ødegård
authors.forename: Trond
authors.initials: T
authors.lastname: Sand
authors.forename: Morten
authors.initials: M
authors.lastname: Engstrøm
authors.forename: John-Anker
authors.initials: JA
authors.lastname: Zwart
authors.forename: Knut
authors.initials: K
authors.lastname: Hagen
mesh_terms: D002908:Chronic Disease; D015331:Cohort Studies; D003625:Data Collection; D005260:Female; D006261:Headache / Q000150:complications* / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D059352:Musculoskeletal Pain / Q000150:complications* / Q000453:epidemiology; D009664:Norway / Q000453:epidemiology; D012307:Risk Factors; D007319:Sleep Initiation and Maintenance Disorders / Q000453:epidemiology / Q000209:etiology*