Seasonal variation in symptoms of depression: A Canadian population based study

Background: There is no consensus as to whether depressive symptoms vary by season. Using data from the Canadian Community Health Survey (CCHS), the purpose of this study was to evaluate seasonal variation in depressive symptoms in the Canadian household population. Methods: A cross-sectional analysis of data from the CCHS in 2015 and 2016 was used. Mean Patient Health Questionnaire-9 (PHQ-9) scores, and categories defined by 5+ or 10+ cut-points were used for analysis. Seasonal effects were assessed using quadratic terms in regression models, generalized linear models were used for this purpose. Models were stratified by youth ages 12-24 (rounded n approximate to 8000) and adults ages 25 + (rounded n approximate to 45,000). Results: Significant seasonal variation was observed for youth (age 12-24) for mean PHQ-9 scores and proportion with scores of 5+ . There was evidence of effect modification by age. The youth group had stronger seasonal effects compared to respondents age 25+. Seasonal effect was highly significant for mean PHQ-9 scores (p = 0.009) and 5+ (p = 0.001), but not for 10+ (p = 0.481). Limitations: Use of cross-sectional data limits the capacity to generalize results to the classic definition of Seasonal Affective Disorder. Data surrounding respondent's anti-depressant use was unavailable. Conclusions: Seasonal variation in depressive symptoms is evident in the Canadian population. Higher levels of symptoms were reported in winter months compared to summer months. The seasonal trend is most pronounced in youth specifically those who reported at least mild depressive symptoms, but not in respondents reporting moderate to severe symptoms.