title: Timing of light exposure and activity in adults with delayed sleep-wake phase disorder.
abstract: OBJECTIVE
  To characterize the patterns of light exposure and physical activity level and assess their relationship with sleep quality and depressive symptoms in adults with delayed sleep-wake phase disorder (DSWPD).
  
  
  METHODS
  42 DSWPD (22 female, mean age 34.5 y) and 26 (±4 years) age-and-sex-matched controls (12 female, mean age 33.4 y) underwent seven days of light and activity monitoring.
  
  
  RESULTS
  Individuals with DSWPD had significantly delayed bed times and wake times, but similar sleep duration compared to controls. Subjective sleep quality (Pittsburgh Sleep Quality Index (PSQI)) was poorer in DSWPDs compared to controls. Those with DSWPD had significantly more activity and light exposure late at night (2:00-4:00) and significantly less activity and light exposure in the morning (8:00-11:00). Total 24 h levels of light and activity were not significantly different between DSWPD and controls. However, the DSWPD group had significantly more light exposure than controls 22 h after waking, during their sleep period. Later light exposure correlated with higher depression scores [Beck Depression Index (BDI)] and poorer sleep quality (PSQI).
  
  
  CONCLUSIONS
  The light exposure patterns observed in DSWPD likely contribute to and perpetuate the chronically delayed sleep and wake phase in these patients. In addition, increased light exposure during the sleep period may also contribute to the poor sleep quality and mood disorders that are common in these individuals.
authors.affiliation: Department of Neurology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA; Department of Neurology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.
authors.forename: Eun Yeon
authors.initials: EY
authors.lastname: Joo
authors.affiliation: Department of Neurology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA.
authors.forename: Sabra M
authors.initials: SM
authors.lastname: Abbott
authors.affiliation: Department of Neurology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA.
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Reid
authors.affiliation: Institute for Minority Health Research, University of Illinois, Chicago, IL, USA.
authors.forename: Donghong
authors.initials: D
authors.lastname: Wu
authors.affiliation: Department of Preventive Medicine, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Kang
authors.affiliation: Department of Neurology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA.
authors.forename: John
authors.initials: J
authors.lastname: Wilson
authors.affiliation: Department of Neurology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA. Electronic address: p-zee@northwestern.edu.
authors.forename: Phyllis C
authors.initials: PC
authors.lastname: Zee
mesh_terms: D000328:Adult; D015444:Exercise; D005260:Female; D006801:Humans; D008029:Lighting; D008297:Male; D020178:Sleep Disorders, Circadian Rhythm
keywords: Actigraphy; Activity; Circadian rhythm; Delayed sleep wake phase disorder; Light