title: Exposure to light at night and risk of depression in the elderly.
abstract: BACKGROUND
  Recent advances in understanding the fundamental links between chronobiology and depressive disorders have enabled exploring novel risk factors for depression in the field of biological rhythms. Increased exposure to light at night (LAN) is common in modern life, and LAN exposure is associated with circadian misalignment. However, whether LAN exposure in home settings is associated with depression remains unclear.
  
  
  METHODS
  We measured the intensities of nighttime bedroom light and ambulatory daytime light along with overnight urinary melatonin excretion (UME) in 516 elderly individuals (mean age, 72.8). Depressive symptoms were assessed using the Geriatric Depression Scale.
  
  
  RESULTS
  The median nighttime light intensity was 0.8lx (interquartile range, 0.2-3.3). The depressed group (n=101) revealed significantly higher prevalence of LAN exposure (average intensity, ≥ 5 lx) compared with that of the nondepressed group (n=415) using a multivariate logistic regression model adjusted for daytime light exposure, insomnia, hypertension, sleep duration, and physical activity [adjusted odds ratio (OR): 1.89; 95% confidence interval (CI), 1.10-3.25; P=0.02]. Consistently, another parameter of LAN exposure (duration of intensity ≥ 10 lx, ≥ 30 min) was significantly more prevalent in the depressed than in the nondepressed group (adjusted OR: 1.71; 95% CI, 1.01-2.89; P=0.046). In contrast, UME was not significantly associated with depressive symptoms.
  
  
  CONCLUSIONS
  Cross-sectional analysis.
  
  
  CONCLUSIONS
  These results suggested that LAN exposure in home settings is significantly associated with depressive symptoms in the general elderly population. The risk of depression may be reduced by keeping nighttime bedroom dark.
authors.affiliation: Department of Community Health and Epidemiology, Nara Medical University School of Medicine, Nara, Japan. obayashi@naramed-u.ac.jp
authors.forename: Kenji
authors.initials: K
authors.lastname: Obayashi
authors.forename: Keigo
authors.initials: K
authors.lastname: Saeki
authors.forename: Junko
authors.initials: J
authors.lastname: Iwamoto
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Ikada
authors.forename: Norio
authors.initials: N
authors.lastname: Kurumatani
mesh_terms: D000368:Aged; D002940:Circadian Rhythm; D003430:Cross-Sectional Studies; D003863:Depression / Q000209:etiology*; D005260:Female; D006801:Humans; D008027:Light / Q000009:adverse effects*; D008297:Male; D008550:Melatonin / Q000652:urine; D011569:Psychiatric Status Rating Scales; D012307:Risk Factors
chemical_list: D008550:Melatonin
keywords: Circadian rhythm; Daytime light; Depression; Elderly; Light at night; Melatonin