Self-reported seasonal variation in depression at 78 degree north. The Svalbard Study

To explore and compare the one year prevalence of self-reported depression in two ethnically different populations.

A cross-sectional study of each population (1988-89 and 1993).

Norwegians living in Longyearbyen, Svalbard, and Russians living in Barentsburg and Pyramiden, Svalbard, both representing the world's two northern most regularly inhabited settlements.

506 Norwegians (327 men and 179 women) and 446 Russians (314 men and 132 women), all 18 years or older, living on Svalbard.

Among Russians, the one year prevalence of self-reported depression lasting for at least 2 weeks was 26.8% for men and 44.7% for women. Corresponding figures for the Norwegians were 10.7 and 15.6%. For the period with polar night the figures were 5.5 and 6.7% for Norwegians, and 21.7 and 37.1% for Russian men and women, respectively. Depression was most common in the youngest age-group among Russians and in the oldest age-group among the Norwegians.

The one year prevalence of depression was 2-3 times higher among Russians compared to Norwegians living on Svalbard. For the period with polar night, the figures were 4-5 times higher for Russians. As both populations are exposed to the same amount of daylight, seasonal depression may therefor not solely be a matter of lack of daylight. Because the Russian population came from lower latitudes than the Norwegians, we hypothesize that insufficient acclimatization after migration to the north is essential for the understanding of seasonal variation in depression.