title: Exposure to light at night, nocturnal urinary melatonin excretion, and obesity/dyslipidemia in the elderly: a cross-sectional analysis of the HEIJO-KYO study.
abstract: BACKGROUND
  Obesity and exposure to light at night (LAN) have increased globally. Although LAN suppresses melatonin secretion and disturbs body mass regulation in experimental settings, its associations with melatonin secretion, obesity, and other metabolic consequences in uncontrolled home settings remain unclear.
  
  
  OBJECTIVE
  The aim of this study was to determine the association of exposure to LAN in an uncontrolled home setting with melatonin secretion, obesity, dyslipidemia, and diabetes.
  
  
  METHODS
  A cross-sectional study was performed in 528 elderly individuals (mean age, 72.8 yr).
  
  
  METHODS
  The intensity of LAN in the bedroom was measured at 1-min intervals during two consecutive nights, along with overnight urinary melatonin excretion and metabolic parameters.
  
  
  RESULTS
  Compared with the Dim group (average <3 lux; n = 383), the LAN group (average ≥3 lux; n = 145) showed significantly higher body weight (adjusted mean, 58.8 vs. 56.6 kg; P = 0.01), body mass index (23.3 vs. 22.7 kg/m(2); P = 0.04), waist circumference (84.9 vs. 82.8 cm; P = 0.01), triglyceride levels (119.7 vs. 99.5 mg/dl; P < 0.01), and low-density lipoprotein cholesterol levels (128.6 vs. 122.2 mg/dl; P = 0.04), and showed significantly lower high-density lipoprotein cholesterol levels (57.4 vs. 61.3 mg/dl; P = 0.02). These associations were independent of numerous potential confounders, including urinary melatonin excretion. Furthermore, LAN exposure is associated with higher odds ratios (ORs) for obesity (body mass index: OR, 1.89; P = 0.02; abdominal: OR, 1.62; P = 0.04) and dyslipidemia (OR, 1.72; P = 0.02) independent of demographic and socioeconomic parameters. In contrast, urinary melatonin excretion and glucose parameters did not show significant differences between the two groups.
  
  
  CONCLUSIONS
  Exposure to LAN in an uncontrolled home setting is associated with impaired obese and lipid parameters independent of nocturnal urinary melatonin excretion in elderly individuals. Moreover, LAN exposure is associated with higher ORs for obesity and dyslipidemia independent of demographic and socioeconomic parameters.
authors.affiliation: Department of Community Health and Epidemiology, Nara Medical University School of Medicine, 840 Shijocho, Kashiharashi, Nara, 634-8521, 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: Nozomi
authors.initials: N
authors.lastname: Okamoto
authors.forename: Kimiko
authors.initials: K
authors.lastname: Tomioka
authors.forename: Satoko
authors.initials: S
authors.lastname: Nezu
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Ikada
authors.forename: Norio
authors.initials: N
authors.lastname: Kurumatani
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002940:Circadian Rhythm / Q000502:physiology; D003430:Cross-Sectional Studies; D050171:Dyslipidemias / Q000150:complications / Q000378:metabolism / Q000652:urine*; D005260:Female; D006801:Humans; D007564:Japan; D008027:Light; D008297:Male; D008550:Melatonin / Q000378:metabolism / Q000652:urine*; D009765:Obesity / Q000150:complications / Q000378:metabolism / Q000652:urine*; D017440:Photoperiod
chemical_list: D008550:Melatonin