Lack of seasonal mood change in the Icelandic population: Results of a cross-sectional study

Objective: The prevalence of seasonal affective disorder-as measured by the Seasonal Pattern Assessment Questionnaire-has been found to be unexpectedly low among Icelanders. The aim of this cross-sectional study was to measure seasonal variations in the prevalence of anxiety and depression among Icelanders assessed with the Hospital Anxiety and Depression Questionnaire. Method: Four 1,000-person cohorts, age 20-70 years, selected at random from the Icelandic National Register, were sent the Hospital Anxiety and Depression Scale by mail in either January, April, July, or October. Only responses from the 4-week period after each mailing were considered in the subsequent analysis. Results: The mean anxiety and depression scores in winter were not higher than those in summer for either sex. There was no significant difference between winter and summer in rates of actual or borderline cases of anxiety or depression or for the two categories combined. Conclusions: This lack of seasonality in anxiety and depression is in sharp contrast to findings from similar cross-sectional studies and may reflect the low propensity for seasonal affective disorder that has been described in the Icelandic population.