title: Heart rate variability and the metabolic syndrome: a systematic review of the literature.
abstract: BACKGROUND
  A number of cross-sectional studies have examined associations between heart rate variability and metabolic syndrome, but differences in study populations, data collection and analysis methodologies make synthesis difficult. The purpose of this study was to systematically review published primary research examining associations between heart rate variability and metabolic syndrome or its individual risk factors.
  
  
  METHODS
  A systematic literature search of PubMed and EMBASE was conducted to identify relevant articles published from January 1999 to December 2012. Studies were included if they examined associations between heart rate variability analysed by standard protocols and metabolic syndrome risk factors according to published definitions. All papers were scored with a modified Downs and Black instrument, and data were extracted.
  
  
  RESULTS
  Fourteen studies were included. Heart rate variability generally was reduced in women with metabolic syndrome compared to those without, while results in men were inconsistent. Time and frequency domain heart rate variability parameters were associated with individual metabolic syndrome risk factors, though sex differences exist. Only two studies considered nonlinear and Poincaré plot heart rate variability parameters, which were reduced in metabolic syndrome.
  
  
  CONCLUSIONS
  Heart rate variability is altered differently in men and women with metabolic syndrome. Future studies should follow consistent heart rate variability analysis protocols and metabolic syndrome definitions and include more comprehensive analyses to investigate potential mechanisms.
authors.affiliation: School of Kinesiology, The University of Western Ontario, London, ON, Canada; Aging, Rehabilitation and Geriatric Care Research Centre, Lawson Health Research Institute, London, ON, Canada.
authors.forename: Melanie I
authors.initials: MI
authors.lastname: Stuckey
authors.forename: Mikko P
authors.initials: MP
authors.lastname: Tulppo
authors.forename: Antti M
authors.initials: AM
authors.lastname: Kiviniemi
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Petrella
mesh_terms: D001342:Autonomic Nervous System Diseases / Q000453:epidemiology / Q000209:etiology*; D002318:Cardiovascular Diseases / Q000453:epidemiology / Q000209:etiology; D005260:Female; D006339:Heart Rate; D006352:Heart Ventricles / Q000503:physiopathology*; D006801:Humans; D008297:Male; D024821:Metabolic Syndrome / Q000453:epidemiology / Q000503:physiopathology*; D012307:Risk Factors; D012727:Sex Characteristics; D018754:Ventricular Dysfunction / Q000453:epidemiology / Q000209:etiology*
keywords: autonomic nervous system; cardiovascular risk; heart rate variability; metabolic syndrome