title: Circadian variation of melatonin, light exposure, and diurnal preference in day and night shift workers of both sexes.
abstract: BACKGROUND
  Light-at-night has been shown in experimental studies to disrupt melatonin production but this has only partly been confirmed in studies of night shift workers. In this cross-sectional study, we examined the circadian variation of melatonin in relation to shift status, individual levels of light-at-night exposure, and diurnal preference, an attribute reflecting personal preference for activity in the morning or evening.
  
  
  METHODS
  One hundred and seventeen workers (75 night and 42 day) of both sexes, ages 22 to 64 years, were recruited from four companies. Participants collected urine samples from all voids over 24 hours and wore a data logger continuously recording their light exposure. Sociodemographic, occupational, lifestyle, and diurnal preference information were collected by interview. Concentrations of urinary 6-sulfatoxymelatonin (aMT6s), the main melatonin metabolite, were measured.
  
  
  RESULTS
  Mean aMT6s levels were lower in night [10.9 ng/mg creatinine/hour; 95% confidence interval (CI), 9.5-12.6] compared with day workers (15.4; 95% CI, 12.3-19.3). The lowest aMT6s levels were observed in night workers with morning preference (6.4; 95% CI, 3.0-13.6). Peak time of aMT6s production occurred 3 hours later in night (08:42 hour, 95% CI, 07:48-09:42) compared with day workers (05:36 hour, 95% CI, 05:06-06:12). Phase delay was stronger among subjects with higher light-at-night exposure and number of nights worked.
  
  
  CONCLUSIONS
  Night shift workers had lower levels and a delay in peak time of aMT6s production over a 24-hour period. Differences were modified by diurnal preference and intensity of light-at-night exposure.
  
  
  CONCLUSIONS
  Night shift work affects levels and timing of melatonin production and both parameters may relate to future cancer risk.
authors.affiliation: Authors' Affiliations: Centre for Research in Environmental Epidemiology (CREAL); IMIM (Hospital del Mar Medical Research Institute); Universitat Pompeu Fabra, Barcelona (UPF); CIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain; kpapantoniou@creal.cat.
authors.forename: Kyriaki
authors.initials: K
authors.lastname: Papantoniou
authors.affiliation: IMIM (Hospital del Mar Medical Research Institute);
authors.forename: Oscar J
authors.initials: OJ
authors.lastname: Pozo
authors.affiliation: Authors' Affiliations: Centre for Research in Environmental Epidemiology (CREAL); IMIM (Hospital del Mar Medical Research Institute); Universitat Pompeu Fabra, Barcelona (UPF); CIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain;
authors.forename: Ana
authors.initials: A
authors.lastname: Espinosa
authors.affiliation: IMIM (Hospital del Mar Medical Research Institute);
authors.forename: Josep
authors.initials: J
authors.lastname: Marcos
authors.affiliation: Authors' Affiliations: Centre for Research in Environmental Epidemiology (CREAL); IMIM (Hospital del Mar Medical Research Institute); Universitat Pompeu Fabra, Barcelona (UPF); CIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain;
authors.forename: Gemma
authors.initials: G
authors.lastname: Castaño-Vinyals
authors.affiliation: Authors' Affiliations: Centre for Research in Environmental Epidemiology (CREAL); IMIM (Hospital del Mar Medical Research Institute); Universitat Pompeu Fabra, Barcelona (UPF); CIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain;
authors.forename: Xavier
authors.initials: X
authors.lastname: Basagaña
authors.affiliation: Departament d'Empresa i Ocupacio;
authors.forename: Ferran Calduch
authors.initials: FC
authors.lastname: Ribas
authors.affiliation: Parc de Salut Mar;
authors.forename: Joan
authors.initials: J
authors.lastname: Mirabent
authors.affiliation: Ferrocarrils de la Generalitat de Catalunya;
authors.forename: Jordi
authors.initials: J
authors.lastname: Martín
authors.affiliation: SEAT, S.A.;
authors.forename: Gemma
authors.initials: G
authors.lastname: Carenys
authors.affiliation: Hospital de Viladecans, Barcelona;
authors.forename: Celia Reyes
authors.initials: CR
authors.lastname: Martín
authors.affiliation: Chronobiology, University of Surrey, Guildford, United Kingdom; and.
authors.forename: Benita
authors.initials: B
authors.lastname: Middleton
authors.affiliation: Chronobiology, University of Surrey, Guildford, United Kingdom; and.
authors.forename: Debra J
authors.initials: DJ
authors.lastname: Skene
authors.affiliation: Authors' Affiliations: Centre for Research in Environmental Epidemiology (CREAL); IMIM (Hospital del Mar Medical Research Institute); Universitat Pompeu Fabra, Barcelona (UPF); CIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain; National School of Public Health, Athens, Greece.
authors.forename: Manolis
authors.initials: M
authors.lastname: Kogevinas
mesh_terms: D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D008875:Middle Aged; D017440:Photoperiod; D011863:Radioimmunoassay; D014940:Work Schedule Tolerance; D055815:Young Adult
chemical_list: C054513:6-sulfatoxymelatonin; D008550:Melatonin