Associations between seasonal variations in day length (photoperiod), sleep timing, sleep quality and mood: a comparison between Ghana (5°) and Norway (69°)

J Sleep Res. 2012 Apr;21(2):176-84. doi: 10.1111/j.1365-2869.2011.00982.x. Epub 2011 Nov 10.

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.

Publication types

  • Comparative Study

MeSH terms

  • Adult
  • Affect / physiology*
  • Anxiety / physiopathology
  • Climate
  • Depression / physiopathology
  • Female
  • Ghana / epidemiology
  • Humans
  • Male
  • Middle Aged
  • Norway / epidemiology
  • Photoperiod*
  • Seasons*
  • Sleep / physiology*
  • Surveys and Questionnaires
  • Time Factors
  • Young Adult