A large Australian study suggests that disrupted body-clock timing may define a distinct pattern of depression for some people. The proposed subtype, called circadian depression, is associated with late sleep schedules, difficulty waking and feeling more alert in the evening.
Researchers at the University of Sydney analyzed survey and genetic data from 11,380 people with a history of depression. Of these, 2,604--about 23 percent--met at least three of six criteria, including an evening preference, extended sleep during depressive periods, morning fatigue, seasonal mood changes and a mismatch between natural sleep timing and work or school schedules.
On average, people in this group said their depression began earlier than others in the study. They also reported more recurring episodes. The researchers found that standard antidepressants were rated as somewhat less effective by this group, although the study did not test treatments directly.
Why timing may matter
The body's circadian clock responds to light and helps regulate sleep, alertness, appetite and mood. When its timing conflicts with daily obligations, a person may experience a persistent form of social jet lag. The researchers suggest that considering sleep timing could add useful context to depression assessments.
The proposed subtype is not yet an established diagnosis, and the findings do not show that clock-based treatments work better for people meeting these criteria. Further research, including clinical trials, is needed. The study appeared in The British Journal of Psychiatry.
Future research may clarify whether measuring circadian rhythms can help clinicians tailor depression care more precisely.
