Seasonal mood variation among Japanese residents of Stockholm.

Depressive symptoms estimated by the Beck Depression Inventory (BDI) were examined in winter and summer in a total of 242 Japanese adults staying less than 2 years or longer than 10 years in Stockholm, where the length of daylight changes dramatically throughout the winter and summer seasons. In spite of the difference in the period of residency, both groups of subjects showed more mental and somatic depressive symptoms in the winter than in the summer. Moreover, the winter BDI score of long stayers was significantly higher than that of short stayers. Accordingly, our results suggest that, although seasonal mood variation is essentially produced by a chronobiological factor, Swedish lifestyle to which long stayers have been accustomed also influences the seasonal mood variation.