An Australian depression study has linked a proposed sleep-timing profile to earlier illness onset and lower patient ratings of common antidepressants, offering a research path that is not yet ready for clinical use.
In an analysis published Oct. 20 in The British Journal of Psychiatry, a University of Sydney-led team classified 2,604 of 11,380 adults, or 23%, under criteria for what researchers call “circadian depression.” The study drew on surveys and genetic data from people with a history of depression.
The classification required participants to report at least three of six features. They included seasonal changes, delayed sleep timing, a preference for evening hours, sleeping more during their worst depressive episode, feeling very tired within the first half-hour after waking, and a marked difference in sleep midpoint between workdays and free days. Researchers had proposed the term “circadian depression” before this study; the criteria tested here remain provisional.
Participants in the proposed group reported that their depression began at an average age of 18.68, compared with 23.20 among the others. They also reported more severe symptoms, more medication side effects and lower efficacy ratings for selective serotonin reuptake inhibitors and serotonin-noradrenaline reuptake inhibitors. Those ratings reflected recalled treatment experiences; the study did not assign participants to medications or measure treatment response in a trial.
Genetic risk scores differed between the groups for several traits, including attention-deficit hyperactivity disorder and some metabolic and inflammatory markers. These statistical links do not establish that participants had those conditions.
The findings also have limits for clinical use. Researchers assessed reported sleep habits without directly measuring internal body clocks, and the study cannot determine whether disrupted daily rhythms caused depression. Its 23% figure describes this sample: all analyzed participants had genetically inferred European ancestry, and the group was predominantly made up of people with severe, recurrent depression.
ABC News reported that Philip Mitchell, a scientia professor of psychiatry at the University of New South Wales who was not involved in the study, said the proposed profile was not ready for clinical use. He also noted that its features overlap with those of atypical depression.
The researchers called for independent studies in more diverse groups and tests of whether the profile predicts treatment outcomes. The paper gives no timetable for that work.
