title: Environmental influence of problematic social relationships on adolescents' daily cortisol secretion: a monozygotic twin-difference study.
abstract: BACKGROUND
  This study investigated the potential environmental effects of peer victimization and the quality of relationships with parents and friends on diurnal cortisol secretion in mid-adolescence.
  
  
  METHODS
  This study used the monozygotic (MZ) twin-difference design to control for genetic effects and thus estimate the unique environmental influences on diurnal cortisol. Participants were 136 MZ twin pairs (74 female pairs) for whom cortisol was assessed four times per day over four collection days grouped in a 2-week period in grade 8 (mean age = 14.07 years). Participants also provided self-reports of peer victimization from grade 4 to grade 8 and of the relationship quality with the mother, father and best friend in grade 8.
  
  
  RESULTS
  The expected pattern of diurnal cortisol secretion was observed, with high levels at awakening followed by an increase 30 min later and a progressive decrease subsequently. Controlling for a host of confounders, only within-twin pair differences in peer victimization and a problematic relationship with the mother were significantly linked to twin differences in diurnal cortisol secretion. Specifically, whereas a more problematic mother-child relationship was associated with morning cortisol secretion, peer victimization was linked to cortisol secretion later in the day (diurnal slope).
  
  
  CONCLUSIONS
  Controlling for genetic influences and other confounders, stressful relationships with peers and the mother exert unique and time-specific environmental influences on the pattern of diurnal cortisol secretion in mid-adolescence.
authors: University of Quebec at Montreal and Ste-Justine Hospital Research Center,Montreal, Quebec,Canada.
authors: M
authors: M
authors: Brendgen
authors: University of Montreal and Montreal Mental Health University Institute,Montreal, Quebec,Canada.
authors: I
authors: I
authors: Ouellet-Morin
authors: University of Montreal and Montreal Mental Health University Institute,Montreal, Quebec,Canada.
authors: S J
authors: SJ
authors: Lupien
authors: University of Montreal and Ste-Justine Hospital Research Center,Montreal, Quebec,Canada.
authors: F
authors: F
authors: Vitaro
authors: Laval University,Quebec City, Quebec,Canada.
authors: G
authors: G
authors: Dionne
authors: Laval University,Quebec City, Quebec,Canada.
authors: M
authors: M
authors: Boivin
mesh_terms: D058445:Bullying / Q000706:statistics & numerical data*; D005219:Father-Child Relations; D005260:Female; D033062:Friends / Q000523:psychology*; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D007398:Interpersonal Relations; D008297:Male; D009034:Mother-Child Relations / Q000523:psychology*; D010379:Peer Group; D014430:Twins, Monozygotic / Q000523:psychology
chemical_list: D006854:Hydrocortisone
keywords: Adolescence; diurnal cortisol; monozygotic twin differences; peer victimization; social relationships