title: A population-based study of gastroesophageal reflux disease and sleep problems in elderly twins.
abstract: OBJECTIVE
  Previous studies indicate an association between sleep problems and gastroesophageal reflux disease (GERD). Although both these conditions separately have moderate heritabilities, confounding by genetic factors has not previously been taken into account. This study aimed to reveal the association between sleep problems and GERD, while adjusting for heredity and other potential confounding factors.
  
  
  METHODS
  This cross-sectional population-based study included all 8,014 same-sexed twins of at least 65 years of age and born in Sweden between 1886 and 1958, who participated in telephone interviews in 1998-2002. Three logistic regression models were used 1) external control analysis, 2) within-pair co-twin analysis with dizygotic (DZ) twin pairs discordant for GERD, and 3) within-pair co-twin analysis with monozygotic (MZ) twin pairs discordant for GERD. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated and adjusted for established risk factors for GERD, i.e. sex, age, body mass index (BMI), tobacco smoking, and educational level.
  
  
  RESULTS
  A dose-response association was identified between increasing levels of sleep problems and GERD in the external control analysis. Individuals who often experienced sleep problems had a two-fold increased occurrence of GERD compared to those who seldom had sleep problems (OR 2.0, 95% CI 1.8-2.4). The corresponding association was of similar strength in the co-twin analysis including 356 DZ pairs (OR 2.2, 95% CI 1.6-3.4), and in the co-twin analysis including 210 MZ pairs (OR 1.5, 95% CI 0.9-2.7).
  
  
  CONCLUSIONS
  A dose-dependent association between sleep problems and GERD remains after taking heredity and other known risk factors for GERD into account.
authors.affiliation: Unit of Upper Gastrointestinal Research, Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden. anna.lindam@ki.se
authors.forename: Anna
authors.initials: A
authors.lastname: Lindam
authors.forename: Catarina
authors.initials: C
authors.lastname: Jansson
authors.forename: Helena
authors.initials: H
authors.lastname: Nordenstedt
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Pedersen
authors.forename: Jesper
authors.initials: J
authors.lastname: Lagergren
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D004200:Diseases in Twins / Q000453:epidemiology / Q000235:genetics; D004522:Educational Status; D005260:Female; D005764:Gastroesophageal Reflux / Q000453:epidemiology / Q000235:genetics*; D006801:Humans; D016015:Logistic Models; D008297:Male; D016017:Odds Ratio; D011159:Population Surveillance / Q000379:methods; D012042:Registries / Q000706:statistics & numerical data; D012307:Risk Factors; D012737:Sex Factors; D012893:Sleep Wake Disorders / Q000453:epidemiology / Q000235:genetics*; D012907:Smoking; D013548:Sweden / Q000453:epidemiology; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*