Winter Fatigue and Winter Depression : Prevalence and Treatment with Bright Light

Abstract: The aim of this thesis is to study prevalence of winter depressive mood and treatment effects of bright light for persons with winter fatigue and winter depression. Study I is a cross-sectional survey of a random sample (N=1657) from the general population between 18-65 years of age in Dalarna, Sweden (latitude 60°N). Study II is a similar survey of 17-18 year old students (N=756) in the municipality of Falun. Approximately 20% of both samples report seasonal symptoms, mainly fatigue, lowered mood and increased sleep duration, appetite and weight. Study III examines the effects of treatment in light rooms for persons from the sample in Study I (40 women, 10 men) with clinically assessed Seasonal Affective Disorder (SAD) or subclinical SAD (S-SAD). Subjects were randomised either to an experimental group receiving ten days of bright light treatment or to a three-week waiting-list control condition followed by bright light treatment. There was a >50% reduction of depressed mood in 13 of the 24 subjects in the experimental group, while none of the 24 controls reported a similar reduction. At the one-month follow-up, results were maintained and 39 of 47 subjects were improved >50%. Fatigue and excessive daytime sleepiness, which were high at baseline, were normal/below population norms for 39 of 47 subjects at the one-month follow-up. Mean values for the mental health aspect of health-related quality of life, which were low at baseline, improved and were close to norms at the one-month follow-up. Study IV is a person-oriented subgroup/cluster analysis of the subjects in Study III. A common trait in all three clusters was a high level of fatigue hence the denomination ´Winter Fatigue´ is used for the merged group. Even though the degree of depressive mood and daytime sleepiness differed between the subgroups, all three groups improved following bright light treatment. The results suggest that an increase in fatigue and depressed mood during the winter season is common in the general population. Bright light treatment reduces depressive mood, fatigue and excessive daytime sleepiness and improves health-related quality of life in persons with winter fatigue and winter depression.