title: Glucose metabolism in discordant monozygotic twins for cardiorespiratory fitness.
abstract: OBJECTIVE
  To determine if glucose and insulin concentrations are regulated by cardiorespiratory fitness (VO2max) regardless of their genetic effects.
  
  
  METHODS
  This cross-sectional study enrolled 38 pairs of young monozygotic twins (11 to 18 years-old). All subjects underwent a progressive maximal exercise test on a treadmill to determine the VO2max with gas exchange analysis (MedGraphics VO2000® - Medical Graphics Corp., St. Paul, MN). Blood samples were drawn after fasting to determine glucose and insulin levels. Monozygosity was confirmed by genotyping 15 informative genetic markers. Nine pairs had at least 10mL.kg-1.min-1 difference in VO2max and were divided into the more and less active group, according to their VO2max. Mean differences between more and less active groups were evaluated by Wilcoxon's test for paired data.
  
  
  RESULTS
  On average, twins from the more active group presented a 17% (13.5±3.7mL.kg-1.min-1) higher VO2max compared to their less active siblings. No significant differences were observed between the groups for fasting insulin (36.5±34.6 versus 25.3±13.7mg/dL; p<0.813). However, the more active twins had lower fasting glucose than the less active ones (82.9±7.3 versus 86.7±7.6mg/dL; p<0.010).
  
  
  CONCLUSIONS
  In this case-control study (discordant monozygotic twins), the less active co-twins were characterized by higher fasting plasma glucose levels. This implies that poor cardiorespiratory fitness can be associated with defective glucose metabolism regardless of genetic factors.
authors.affiliation: Departamento de Análises Clínicas e Toxicológicas, USP, São Paulo, SP, Brasil. queirogamr@hotmail.com
authors.forename: Marcos Roberto
authors.initials: MR
authors.lastname: Queiroga
authors.forename: Ricardo Augusto
authors.initials: RA
authors.lastname: Barbieri
authors.forename: Sandra Aires
authors.initials: SA
authors.lastname: Ferreira
authors.forename: André Ducati
authors.initials: AD
authors.lastname: Luchessi
authors.forename: Vivian Nogueira
authors.initials: VN
authors.lastname: Silbiger
authors.forename: Rosario Dominguez C
authors.initials: RD
authors.lastname: Hirata
authors.forename: Mario Hiroyuki
authors.initials: MH
authors.lastname: Hirata
authors.forename: Eduardo
authors.initials: E
authors.lastname: Kokubun
mesh_terms: D000293:Adolescent; D016022:Case-Control Studies; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D005947:Glucose / Q000378:metabolism*; D006321:Heart / Q000502:physiology*; D006801:Humans; D008297:Male; D010809:Physical Fitness; D012143:Respiratory Physiological Phenomena; D014430:Twins, Monozygotic
chemical_list: D005947:Glucose