Associations between seasonal variations in day length (photoperiod), sleep timing, sleep quality and mood: a comparison between Ghana (5°) and Norway (69°)
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.
Document Type: Research Article
Affiliations: Department of Psychology, University of Ghana, Accra, Ghana
Publication date: April 1, 2012