Previous studies identified seasonal symptoms in mood disorders (recurrent depression, and bipolar disorder I and II). In this study we tested the dual vulnerability hypothesis, assessed the seasonal changes and the presence of depressive symptoms.
8028 subjects aged 30 to 99, 55% women and 45% men were interviewed and invited to the health examination. The process was: a) interview at home, b) health examination at the local health centre, c) telephone interview and/or a mail questionnaire, d) Registration of information for baseline and follow-up purposes. The questionnaires analyzed for this study were Beck Depression Inventory (BDI) and Seasonal Pattern Assessment Questionnaire (SPAQ). Surveys were applied by 5 field teams in 80 Finnish regions.
The prevalence of seasonal symptoms together with depression was 9%. Individuals with a high BDI score and a low SPAQ comprised 19% against those 11% having low BDI and a high SPAQ, which makes 30%. Sum scores correlated (r=.31, p<001) corrected for gender and age. In logistic regression models, higher scores on the SPAQ were associated with depression (OR=2.76, 95% CI of 2.41- 3.18) and higher scores on the BDI with the seasonal pattern (OR=2.76, 95% CI of 2.40-3.18).
Our results now extend the findings of  that 10% of all mood disorders followed a seasonal pattern. Therefore, a seasonal pattern can be detected not just in clinical, but in general populations, too.