title: A twin study of metabolic syndrome and autonomic tone.
abstract: BACKGROUND
  One possible mechanism of higher cardiovascular mortality associated with the metabolic syndrome (MetS) may be through abnormal modulation in autonomic tone.
  
  
  RESULTS
  We examined the association between the MetS and autonomic tone as measured by heart rate variability (HRV) among 288 twins from the Twins Heart Study (THS). Of the 288 participants, 151 (52%) had the MetS. The MetS was associated with decreased HRV across all frequency ranges, and each additional MetS risk factor was associated with lower HRV. After adjustment for several potential confounders, very-low frequency (P < 0.001), low frequency (P < 0.001), and total power (P = 0.02) spectra of HRV remained significantly lower in twins with a progressively higher number of MetS components (18-50% decrease comparing twins with 5 risk factors to those with no risk factors). Among 87 twin pairs who were discordant for the number of MetS components, a one-unit increment in MetS components was associated with an 8% smaller very-low frequency (p = 0.03) and a 15% smaller low frequency spectrum (P = 0.002) comparing each twin with his brother.
  
  
  CONCLUSIONS
  MetS was associated with lower HRV in a well-characterized sample of middle-aged male twins. This association persisted even after controlling for genetic and shared environmental factors accounted for by comparison within twin pairs. Abnormalities of autonomic tone, as evidenced by lower HRV, may be partly responsible for the higher rate of atrial fibrillation, coronary heart disease, cardiac death, and overall mortality seen in patients with the MetS.
authors.affiliation: Division of Cardiology, Department of Medicine, University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, North Carolina 27599-7075, USA. anilgehi@gmail.com
authors.forename: Anil K
authors.initials: AK
authors.lastname: Gehi
authors.forename: Rachel
authors.initials: R
authors.lastname: Lampert
authors.forename: Emir
authors.initials: E
authors.lastname: Veledar
authors.forename: Forrester
authors.initials: F
authors.lastname: Lee
authors.forename: Jack
authors.initials: J
authors.lastname: Goldberg
authors.forename: Linda
authors.initials: L
authors.lastname: Jones
authors.forename: Nancy
authors.initials: N
authors.lastname: Murrah
authors.forename: Ali
authors.initials: A
authors.lastname: Ashraf
authors.forename: Viola
authors.initials: V
authors.lastname: Vaccarino
mesh_terms: D001341:Autonomic Nervous System / Q000503:physiopathology*; D002318:Cardiovascular Diseases / Q000209:etiology* / Q000401:mortality / Q000503:physiopathology; D015536:Down-Regulation; D004562:Electrocardiography; D006339:Heart Rate; D006801:Humans; D008297:Male; D024821:Metabolic Syndrome / Q000150:complications / Q000401:mortality / Q000503:physiopathology*; D008875:Middle Aged; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D014728:Veterans