Seasonal variation in clinical remission of primary care patients with depression: impact of gender.

RATIONALE, AIMS AND

OBJECTIVES

The impact of seasonal variation on clinical remission in patients with depression has not been well studied. The hypothesis for this study was that the clinical remission rate would be lower in the winter comparing to the other seasons, specifically evaluated by gender.

METHODS

The study cohort comprised 2873 primary care patients with depression as a longitudinal retrospective chart review analysis. The sample was limited to patients who were continuing in care; dropouts were excluded from the analysis.

RESULTS

Multivariate logistic regression analysis of the independent variables for those participants who achieved clinical remission demonstrated that for the male patients, the season of diagnosis did not impact the rate of remission at 6 months while controlling for all other independent variables. For female patients, those that were diagnosed with depression in the fall had increased likelihood of 6-month remission compared with those patients diagnosed in the winter months (OR 1.300, CI 1.006-1.680, P=0.045) and the spring and summer patients were not significantly different in their outcome rates. When both genders were combined, the odds of remission at 6 months were not statistically significant for any season of diagnosis.

CONCLUSIONS

This study demonstrates that in patients who were continuing care, women who were diagnosed with major depression or dysthymia in the fall season have improved 6-month clinical outcome of remission compared with those women diagnosed in the winter, when controlling for demographic and clinical characteristics. This effect was not seen in men or when the genders were combined into a single cohort. The assessment of the seasonality effect on depression outcomes requires further long-term follow-up studies.