title: Day-to-day dynamics of associations between sleep, napping, fatigue, and the cortisol diurnal rhythm in women diagnosed as having breast cancer.
abstract: OBJECTIVE
  To examine whether day-to-day variations in sleep behaviors, ongoing sleep disturbance, and fatigue predict the cortisol diurnal rhythm in women recently diagnosed as having early-stage breast cancer.
  
  
  METHODS
  Women (N = 130, mean [standard deviation] age = 55.6 [9.4] years) collected saliva 5×/day/2 days for cortisol. Diaries were used to assess prior-day nap duration, nocturnal awakenings, sleep latency, and morning restfulness. Ongoing fatigue and sleep disturbance were measured using the Multidimensional Fatigue Symptom Inventory and the Pittsburg Sleep Quality Inventory. Data were analyzed using a multilevel growth curve modeling.
  
  
  RESULTS
  Greater ongoing fatigue (b = 0.035, p = .032), or sleep disturbance (b = 0.026, p = .006) predicted a slower cortisol decline. Greater ongoing fatigue also predicted higher awakening cortisol (b = 0.154, p = .030) and lower cortisol awakening response (CAR; b = -0.146, p = .005). Longer prior-day naps predicted higher CAR (b = 0.042, p = .050) and a steeper cortisol decline (b = -0.035, p = .003). Longer sleep latency predicted both a greater cortisol linear decline (b = -0.013, p < .001) and a greater quadratic slope curvature (b = 0.0007, p < .001). Feeling less rested in the morning predicted lower awakening cortisol (b = -0.187, p = .004), higher CAR (b = 0.124, p = .016), and a slower cortisol decline (b = 0.023, p = .042).
  
  
  CONCLUSIONS
  Both daily variations in sleep behaviors and ongoing sleep disturbance and fatigue are associated with a disrupted cortisol rhythm. In contrast, prior-day napping is associated with a more robust cortisol rhythm. These findings are particularly relevant to women with breast cancer who often experience sleep disturbance and fatigue. Additional research is needed to determine causal pathways between sleep disturbance and dysregulation of the hypothalamic-pituitary-adrenal axis in patients with breast cancer.
authors.affiliation: From the Department of Health Promotion (D.T., L.W.J.), Marcella Niehoff School of Nursing, Loyola University Chicago, Maywood, Illinois; and Department of Microbiology Immunology (H.L.M.), Stritch School of Medicine, Loyola University Chicago, Maywood, Illinois.
authors.forename: Dina
authors.initials: D
authors.lastname: Tell
authors.forename: Herbert L
authors.initials: HL
authors.lastname: Mathews
authors.forename: Linda Witek
authors.initials: LW
authors.lastname: Janusek
mesh_terms: D001943:Breast Neoplasms / Q000150:complications / Q000503:physiopathology*; D002940:Circadian Rhythm / Q000502:physiology*; D005221:Fatigue / Q000209:etiology / Q000503:physiopathology*; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000032:analysis / Q000502:physiology*; D008875:Middle Aged; D012463:Saliva / Q000737:chemistry; D012890:Sleep / Q000502:physiology*; D012893:Sleep Wake Disorders / Q000503:physiopathology
chemical_list: D006854:Hydrocortisone