The relationship between chronotype and treatment time of day on post-treatment depression symptom severity for depressed patients receiving cognitive behavioural therapy.

Background: Major depressive disorder (MDD) represents a serious public health problem that affects a quarter billion individuals worldwide. Consequently, there is a need to identify modifiable factors of services that support treatment success. The relationship between circadian preferences (i.e., chronotype), treatment time of day, and outcomes is an understudied research area. Executing optimal treatment timing based on these factors could lead to substantial returns on a modifiable variable.

Method: The present study evaluated the associations between chronotype and treatment time of day on post-treatment depression symptom severity. In a tertiary setting, outpatients with MDD (n = 227) received 14 sessions of cognitive behavioural therapy in a group format, at one of three time of days: morning, afternoon, or evening. Participants completed measures of depression and chronotype at baseline and post-treatment.

Result: Statistically significant increases in morningness were found for the afternoon and evening groups, but not the morning group. There was no significant interaction effect between pre-treatment morningness-eveningness scores and treatment time of day on post-treatment depression scores nor treatment response. However, there was a significant interaction effect of change in morningness-eveningness scores and post-treatment depression severity in the afternoon group.

Limitations: The lack of a control group limits conclusions drawn.

Conclusion: The results suggest that individual circadian phase may impact treatment outcomes in relation to time of day. Further intentionally designed research is warranted to improve understanding of predictors, moderators, and mediators of patient outcomes based on treatment time of day and circadian phase and amplitude.