title: Associations between seasonal variations in day length (photoperiod), sleep timing, sleep quality and mood: a comparison between Ghana (5°) and Norway (69°).
abstract: The hypothesis of whether day length (photoperiod) is an important zeitgeber (time-giver) for keeping the circadian rhythm entrained to a 24-hour cycle was examined, as was its association with sleep patterns and mood problems. Data were collected prospectively from a site with very large differences in daylight duration across seasons (Tromsø in Norway, 69°39'N) and a site with very small seasonal differences in daylight duration (Ghana in Accra, 5°32'N). Two hundred subjects were recruited from both sites in January. At the follow-up in August, 180 and 150 subjects in Ghana and Norway participated, respectively. Use of a weekly sleep diary indicated low to moderately strong seasonal changes in rise- and bedtime, sleep efficiency and sleep onset latency only in the northern latitude. No seasonal changes in sleep duration or night awakenings were observed. The self-report measures indicated moderate to strong seasonal differences in insomnia and fatigue, and weaker differences in depressed mood in Norway, but small to non-existing seasonal differences in Ghana. Lack of daylight was related to phase-delayed rise- and bedtimes, increased problems falling asleep, daytime fatigue and depressive mood. However, total sleep duration and sleep quality appeared unaffected.
authors.affiliation: Department of Psychology, University of Tromsø, Tromsø, Norway. oddgeir.friborg@uit.no
authors.forename: Oddgeir
authors.initials: O
authors.lastname: Friborg
authors.forename: Bjørn
authors.initials: B
authors.lastname: Bjorvatn
authors.forename: Benjamin
authors.initials: B
authors.lastname: Amponsah
authors.forename: Ståle
authors.initials: S
authors.lastname: Pallesen
mesh_terms: D000328:Adult; D000339:Affect / Q000502:physiology*; D001007:Anxiety / Q000503:physiopathology; D002980:Climate; D003863:Depression / Q000503:physiopathology; D005260:Female; D005869:Ghana / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D017440:Photoperiod; D012621:Seasons; D012890:Sleep / Q000502:physiology*; D011795:Surveys and Questionnaires; D013997:Time Factors; D055815:Young Adult