Effect of depression on sleep: Qualitative or quantitative?

BACKGROUND: The present study was designed to assess whether subjective sleep patterns differ between: (i) depressed patients and controls, and (ii) between subjects with different severity of depression. Based on available literature, it was hypothesized that sleep patterns must be different between the above mentioned groups. MATERIALS AND METHODS: This study included 60 subjects with major depressive disorder and 40 subjects in the control group. Subjects with sleep disturbance secondary to any other factor, e.g., medical illness, environmental factors, other psychiatric illness etc, were not included in the study. Depression severity was assessed in the subjects with depression with the help of Beck Depression Inventory II. Subjective sleep complaints were noted in the presence of a reliable informant, preferably bed partner. All the information was recorded in a semistructured performa. Statistical analysis was done with the help of SPSS v 11.0. The Chi square and Fisher exact tests were used for categorical variables; independent t-test and one way ANOVA were applied for numerical variables. Ordinal variables were analyzed using Mann Whitney U and Kruskall-Wallis tests. RESULTS: Depression and control groups were similar in age (P = 0.32) and gender (P = 0.14) distribution. Subjects in the depression group had lesser total sleep time (P = 0.001), longer sleep latency (P = 0.001), frequent awakenings (P = 0.04), greater wake-after-sleep onset and offset times (both P = 0.001), lesser sleep efficiency, and tended to wake up early (Mann Whitney U = 913.5; P = 0.05). Subjects with severe depression were different from the mild and moderate groups with regards to total sleep time (P = 0.002), night-time sleep (P = 0.007), and sleep efficiency (P = 0.001) even when the three groups were comparable in age. CONCLUSION: Depression is associated with sleep disturbances, not only qualitatively, but also quantitatively. Sleep disturbance arises only after a critical level of depression is reached, and depression of varying severity may selectively affect different sleep parameters.