Chronotypes in patients with nonseasonal depressive disorder: Distribution, stability and association with clinical variables.

The individual's chronotype is regarded as rather stable trait with substantial heritability and normal distribution of the "morningness-eveningness" dimension in the general population. Eveningness has been related to the risk of developing affective, particularly depressive, disorders. However, age and other sociobiological factors may influence chronotypes. The present study investigated the distribution, stability, and clinical correlates of chronotype and morningness-eveningness in hospitalized patients with affective disorder. Chronotype was assessed with the morningness-eveningness questionnaire (MEQ) in 93 patients with nonseasonal depressive syndrome (85% major depression; 15% depressive adjustment disorder) after admission, and in 19 patients again before discharge. Distribution, stability and correlations of MEQ scores with clinical variables were calculated. Additionally, a literature analysis of chronotype distributions in samples of nondepressed persons and patients with nonseasonal depression was carried out. MEQ scores (mean 49 ± 11, range 23-75, higher scores indicate morningness) in 93 acutely depressed inpatients (age 41 ± 14 years, range 18-75 years; 63% women; hospitalization 48 ± 22 days; BDI-II 32 ± 11) were normally distributed (Shapiro-Wilk test; W = 0.993, p = 0.920) with 59.1% intermediate types, 19.4% evening types, and 21.5% morning types. MEQ change scores from admission to discharge were nonsignificant (-1.3 ± 5.0; paired t-test, t18 = -1.09; p = 0.29) despite significantly improved depression scores (-19.4 ± 7.6; paired t-test, t18 = 11.2, p < 0.001). Age (r = 0.24), and depression scores (r = -0.21) correlated significantly (p < 0.05) with MEQ scores; associations with sex and hospitalization duration were nonsignificant. The present study and literature findings revealed that the frequency of evening types is not clearly elevated in depression, but morning types are less frequent compared to healthy samples (p < 0.001). Morningness-eveningness scores were normally distributed and stable in depressive inpatients. In line with previous findings, but contrary to theoretical assumptions, evening types were not overrepresented in depressed patients. Additionally, relatively less morning types and more intermediate types were found in depressed patients. Future studies should focus on transitions from morning to intermediate types as a tentative risk or correlate of emerging depression.