The Zurich Study. XIV. Epidemiology of seasonal depression.

In a longitudinal cohort study of young adults from the Canton of Zurich in Switzerland (Zurich Study), seasonal patterns of several psychiatric and psychosomatic syndromes were investigated in two interviews over a period of three years. At an age of 27-28 years, 23% of the depressives, 15% of the neurasthenic subjects, and 14% of the subjects with backache reported an increased susceptibility in autumn and/or winter. With respect to the course we found that 10.4% of the subjects of the longitudinal sample (n = 417) suffered from seasonal depression (including individuals with subsyndromal seasonal difficulties) over two consecutive years. Specific symptoms, such as hypersomnia, increase of appetite or weight gain, were not found to be consistently associated with seasonal depression. A comparison of actual and retrospective reports on seasonal depression resulted in a very low reliability. In view of these results the seasonal subtype of depression should be diagnosed with caution, except when the diagnosis is based on longitudinal observations and/or external sources of information (e.g. family members, partner).