Euthymia scale as a protective factor for depressive symptoms: a one-year follow-up longitudinal study

Objectives This study aimed to examine whether a high score on the euthymia scale (ES) predicts a low incidence of depressive symptoms one year later. Methods The baseline online survey was conducted in February 2020, and a follow-up survey was done in February 2021. Japanese over 20 years old were enrolled. Respondents who answered both baseline and follow-up, and without depressive symptoms at baseline were included in the analysis. The euthymia scores at baseline was measured by the 10 items of the Japanese version of the ES. Depressive symptoms at follow-up were determined if participants showed either depressive feelings or anhedonia. The odds ratio (OR) was calculated using multivariate logistic regression analysis, adjusting for age, gender, marital status, educational attainment, and clinical visit for depressive episode before the baseline survey. Results The total of 624 participants were analyzed. A total of n = 63 (10.1%) presented depressive symptom at follow-up. A high ES score significantly predicted a lower incidence of depressive symptoms, after adjusting for covariates (aOR = 0.81 [95% confidence interval: 0.72–0.89]). Using the cutoff score retrieved from this data, a high ES score (7 or more) showed the same tendency, compared to a low ES score (< 7) (aOR = 0.46 [0.25–0.83]). Conclusions This study suggests the predictive usefulness of euthymia for subsequent depressive symptoms. Further investigation is needed by employing rigid diagnostic criteria.