title: Midday naps and the risk of coronary artery disease: results of the Heinz Nixdorf Recall Study.
abstract: OBJECTIVE
  Several studies have assessed the association between midday nap and cardiovascular outcomes and reported heterogenous results. Concern exists that confounding might have distorted these results and contributed to discrepancies among them. This study prospectively examines the association between midday nap habits and the occurrence of coronary artery disease in a non-Mediterranean population.
  
  
  METHODS
  The baseline examination of 4,123 participants aged 45-75 years.
  
  
  METHODS
  Measurements included interviews, physical examinations, laboratory tests, and electron beam computed tomography. We studied the influence of midday nap habits on risk of coronary artery disease. We adjusted for several potential confounders including measures of subclinical atherosclerosis-such as coronary calcium score and ankle brachial index-at baseline. Cardiac events during a median follow-up of 8.1 years were defined as nonfatal myocardial infarction and sudden cardiac death.
  
  
  RESULTS
  Overall, 135 of 4,123 subjects (3.3%) either suffered from acute myocardial infarction (81 subjects) or died due to a sudden cardiac death (54 subjects) during follow-up. After adjustment for several confounders including measures of subclinical atherosclerosis, regular long (> 60 min) midday nap was associated with an increased hazard ratio of cardiac events (hazard ratio 2.12, 95% confidence interval 1.11-4.05).
  
  
  CONCLUSIONS
  As our detailed confounder analyses showed, confounding is not the sole explanation for this finding. Future research on midday naps should focus on biological mechanisms that may be responsible for increasing the risk of coronary artery disease among subjects taking regular long midday naps.
authors.affiliation: Institute of Clinical Epidemiology, University of Halle-Wittenberg, Halle, Germany. andreas.stang@medizin.uni-halle.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Stang
authors.forename: Nico
authors.initials: N
authors.lastname: Dragano
authors.forename: Susanne
authors.initials: S
authors.lastname: Moebus
authors.forename: Stefan
authors.initials: S
authors.lastname: Möhlenkamp
authors.forename: Axel
authors.initials: A
authors.lastname: Schmermund
authors.forename: Hagen
authors.initials: H
authors.lastname: Kälsch
authors.forename: Raimund
authors.initials: R
authors.lastname: Erbel
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Jöckel
mesh_terms: D000368:Aged; D002940:Circadian Rhythm; D003324:Coronary Artery Disease / Q000175:diagnosis / Q000453:epidemiology*; D016757:Death, Sudden, Cardiac / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D005858:Germany; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D057566:Self Report; D012737:Sex Factors; D012890:Sleep / Q000502:physiology*; D013997:Time Factors