title: Influence of Day Length and Physical Activity on Sleep Patterns in Older Icelandic Men and Women.
abstract: OBJECTIVE
  To identify cross-sectional and seasonal patterns of sleep and physical activity (PA) in community-dwelling, older Icelandic adults using accelerometers.
  
  
  METHODS
  A seven-day free-living protocol of 244 (110 female) adults aged 79.7 ± 4.9 years was conducted as part of a larger population-based longitudinal observational-cohort study in the greater Reykjavik area of Iceland. A subpopulation (n = 72) repeated the 7-day measurement during seasonal periods with greater (13.4 ± 1.4 h) and lesser (7.7 ± 1.8 h) daylight.
  
  
  RESULTS
  Cross-sectional analyses using multiple linear regression models revealed that day length was a significant independent predictor of sleep duration, mid-sleep, and rise time (all p < 0.05). However, the actual within-individual differences in sleep patterns of the repeaters were rather subtle between periods of longer and shorter day-lengths. Compared to women, men had a shorter sleep duration (462 ± 80 vs. 487 ± 68 minutes, p = 0.008), earlier rise time, and a greater number of awakenings per night (46.5 ± 18.3 vs. 40.2 ± 15.7, p = 0.007), but sleep efficiency and onset latency were similar between the two sexes. Daily PA was also similar between men and women and between periods of longer and shorter day-lengths. BMI, age, gender, and overall PA all contributed to the variations in sleep parameters using multiple regression analysis.
  
  
  CONCLUSIONS
  The sleep and PA characteristics of this unique population revealed some gender differences, but there was limited variation in response to significant daylight changes which may be due to long-term adaptation.
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Brychta
authors.affiliation: Research Center of Movement Science, University of Iceland, Reykjavík, Iceland.|Icelandic Heart Association, Kópavogur, Iceland.
authors.forename: Nanna Yr
authors.initials: NY
authors.lastname: Arnardottir
authors.affiliation: Center of Sport and health Sciences, School of Education, University of Iceland, Laugarvatn, Iceland.
authors.forename: Erlingur
authors.initials: E
authors.lastname: Johannsson
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD.
authors.forename: Elizabeth C
authors.initials: EC
authors.lastname: Wright
authors.affiliation: Icelandic Heart Association, Kópavogur, Iceland.
authors.forename: Gudny
authors.initials: G
authors.lastname: Eiriksdottir
authors.affiliation: Icelandic Heart Association, Kópavogur, Iceland.|Faculty of Medicine, University of Iceland, Reykjavík, Iceland.
authors.forename: Vilmundur
authors.initials: V
authors.lastname: Gudnason
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD.
authors.forename: Catherine R
authors.initials: CR
authors.lastname: Marinac
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD.
authors.forename: Megan
authors.initials: M
authors.lastname: Davis
authors.affiliation: Department of Social Medicine, CAPHRI School for Public Health and Primary Care, Maastricht University, Maastricht, The Netherlands.
authors.forename: Annemarie
authors.initials: A
authors.lastname: Koster
authors.affiliation: Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Denmark.
authors.forename: Paolo
authors.initials: P
authors.lastname: Caserotti
authors.affiliation: Research Center of Movement Science, University of Iceland, Reykjavík, Iceland.
authors.forename: Thorarinn
authors.initials: T
authors.lastname: Sveinsson
authors.affiliation: National Institute on Aging, Bethesda, Maryland.
authors.forename: Tamara
authors.initials: T
authors.lastname: Harris
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD.
authors.forename: Kong Y
authors.initials: KY
authors.lastname: Chen
mesh_terms: D056044:Actigraphy; D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007055:Iceland; D008297:Male; D017440:Photoperiod; D012621:Seasons; D012737:Sex Factors; D012890:Sleep / Q000502:physiology*; D013997:Time Factors
keywords: accelerometer; aging; physical activity; seasonal; total sleep time