title: Lower melatonin secretion in older females: gender differences independent of light exposure profiles.
abstract: BACKGROUND
  Melatonin is associated with a variety of diseases in advanced age, including insomnia, depression, and dementia, and its secretion is influenced by light exposure. Although studies in young and middle-aged subjects have shown that females tend to have higher melatonin levels than males, gender differences in melatonin levels among older people remain unclear.
  
  
  METHODS
  To determine the gender differences in melatonin levels among older people in home settings, we conducted a cross-sectional study in 528 older people. We measured overnight urinary 6-sulfatoxymelatonin excretion (UME; an index of melatonin secretion), and ambulatory light intensity.
  
  
  RESULTS
  The mean age of females was 1.8 years younger, and average intensity of daytime light exposure was half that in males (P < 0.01). In a univariate comparison, UME was significantly lower in females than in males (P < 0.01). A multivariate model using analysis of covariance showed that log-transformed UME remained significantly lower in females after adjustment for potential confounding factors, including age and daytime and nighttime light exposure profiles (males vs. females: 1.90 vs. 1.73 log µg; adjusted mean difference 0.17 log µg [95% confidence interval [CI] 0.02-0.32]; P = 0.02). This result indicates that older females have 18.4% (95% CI, 2.2-37.4%) lower UME than older males.
  
  
  CONCLUSIONS
  Older females have significantly lower UME than older males, an association which is independent of light exposure profiles in home settings. Our findings may be useful as basic data for further research to investigate gender differences in several diseases associated with melatonin in the elderly.
authors.affiliation: Department of Community Health and Epidemiology, Nara Medical University School of Medicine.
authors.forename: Kenji
authors.initials: K
authors.lastname: Obayashi
authors.forename: Keigo
authors.initials: K
authors.lastname: Saeki
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Tone
authors.forename: Junko
authors.initials: J
authors.lastname: Iwamoto
authors.forename: Kimie
authors.initials: K
authors.lastname: Miyata
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; D001683:Biological Clocks / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008029:Lighting / Q000706:statistics & numerical data*; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives / Q000652:urine*; D008875:Middle Aged; D012737:Sex Factors
chemical_list: D008550:Melatonin