BACKGROUND: Eveningness is associated with depression diagnosis and increased depressive symptom severity. Time-of-day preference has been linked with differences in cognitive function in the general population, with cognitive difficulties being a major factor in psychosocial impairment in depression. We therefore investigated the impact of time-of-day preference and self-reported depressed state on subjective cognitive function.
METHODS: Participants over the age of 18 with a self-reported history of depression completed an online questionnaire. They provided demographic and mental health information, and completed self-report scales assessing depression symptoms, time-of-day preference, and cognition. Participants were classified as "currently" or "previously depressed" based on self-reported symptoms, and as having a morning, neither, or evening time-of-day preference.
RESULTS: A total of 804 participants reporting a history of unipolar depression were included. Currently-depressed participants reported more cognitive difficulties in all areas measured. Evening types reported more complex attentional and retrospective memory difficulties than neither types, and reported more executive and prospective memory difficulties than both neither and morning types. There was an additive effect of mood state and time-of-day preference, with self-reported depressed evening types reporting the most cognitive problems.
LIMITATIONS: Depression history, time-of-day preference, and cognitive function were assessed using unsupervised self-report measures. Time-of-day preference does not necessarily reflect the physiological circadian system.
CONCLUSIONS: Both depressed state and evening preference were individually associated with subjective cognitive complaints in people with a self-reported history of unipolar depression. The additive effect of poor mood and eveningness is important given the high prevalence of eveningness in depression. Assessment of time-of-day preference could help to identify those susceptible to cognitive symptoms, and inform treatment.
