Chronotype in bipolar disorder: an 18-month prospective study.

Objective: Circadian dysregulation plays an important role in the etiology of mood disorders. Evening chronotype is frequent in these patients. However, prospective studies about the influence of chronotype on mood symptoms have reached unclear conclusions in patients with bipolar disorder (BD). The objective of this study was to investigate relationship between chronotype and prognostic factors for BD. Methods: At the baseline, 80 euthymic BD patients answered a demographic questionnaire and clinical scales to evaluate anxiety, functioning and chronotype. Circadian preference was measured using the Morningness-Eveningness Questionnaire, in which lower scores indicate eveningness. Mood episodes and hospitalizations were evaluated monthly for 18 months. Results: Among the BD patients, 14 (17.5%) were definitely morning type, 35 (43.8%), moderately morning, 27 (33.7%) intermediate (neither) and 4 (5%) moderately evening. Eveningness was associated with obesity or overweight (p = 0.03), greater anxiety (p = 0.002) and better functioning (p = 0.01), as well as with mood episodes (p = 0.04), but not with psychiatric hospitalizations (p = 0.82). This group tended toward depressive episodes (p = 0.06), but not (hypo)mania (p = 0.56). Conclusion: This study indicated that evening chronotype predicts a poor prognostic for BD. It reinforces the relevance of treating rhythm disruptions even during euthymia to improve patient quality of life and prevent mood episodes.