title: The relationship between light exposure and sleep, fatigue, and depression in cancer outpatients: test of the mediating effect.
abstract: BACKGROUND
  Light is an important cue for the entrainment of circadian rhythms, which can be related to sleep quality, fatigue, and depression in cancer patients.
  
  
  OBJECTIVE
  The purpose of this study was to determine the effects of light exposure on sleep quality, fatigue, and depression in cancer patients, to test whether the effect of light exposure on sleep quality, fatigue, and depression was mediated by the other 2 symptoms.
  
  
  METHODS
  This was a cross-sectional study for which we recruited 163 cancer outpatients. For 3 consecutive days, they wore an Actiwatch to measure light exposure. Instruments included the Pittsburgh Sleep Quality Index-Taiwan form, the Brief Fatigue Inventory-Taiwan form, and the Beck Depression Inventory II-Taiwan version.
  
  
  RESULTS
  The results indicated that the Pittsburgh Sleep Quality Index-Taiwan form score was significantly and negatively correlated with minutes of light exposure (MLE) of 1000 lux or greater (r = -0.61, P < .001) and the intensity of light exposure under activity (r = -0.59, P < .001). Fatigue was negatively correlated with MLE (r = -0.18, P = .03). Depression was also negatively correlated with MLE and intensity of light exposure (both r = -0.18, P = .02). Most important, the effect of light exposure on sleep quality, fatigue, and depression was mediated by the other 2 symptoms.
  
  
  CONCLUSIONS
  Light exposure appeared to be a shared factor for the co-occurrence of fatigue, sleep disturbances, and depression.
  
  
  CONCLUSIONS
  Light exposure has great potential for improving sleep quality as well as ameliorating fatigue and depression in cancer outpatients.
authors.affiliation: Author Affiliations: Department of Nursing, Yuanpei University, Hsinchu, Taiwan (Dr Sun); Department of Hospice and Palliative Care (Dr Wu) and Cancer Center and Department of Radiation Oncology (Dr Chiou), Taipei Medical University Hospital, Taiwan; Graduate Institute of Nursing (Drs Sun and Chang) and School of Nursing (Dr Lin), College of Nursing, Taipei Medical University, Taiwan; and Nursing Department, Chung-Hwa University of Medical Technology, Tainan, Taiwan (Dr Chou).
authors.forename: Jia-Ling
authors.initials: JL
authors.lastname: Sun
authors.forename: Shen-Chi
authors.initials: SC
authors.lastname: Wu
authors.forename: Lu-I
authors.initials: LI
authors.lastname: Chang
authors.forename: Jeng-Fong
authors.initials: JF
authors.lastname: Chiou
authors.forename: Pi-Ling
authors.initials: PL
authors.lastname: Chou
authors.forename: Chia-Chin
authors.initials: CC
authors.lastname: Lin
mesh_terms: D056044:Actigraphy / Q000706:statistics & numerical data; D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D003863:Depression / Q000175:diagnosis / Q000209:etiology*; D005221:Fatigue / Q000175:diagnosis / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000150:complications / Q000451:nursing / Q000628:therapy*; D010045:Outpatients / Q000523:psychology; D017440:Photoperiod; D011569:Psychiatric Status Rating Scales; D011788:Quality of Life; D012890:Sleep / Q000502:physiology; D012893:Sleep Wake Disorders / Q000175:diagnosis / Q000209:etiology; D011795:Surveys and Questionnaires