New 'Circadian' Subtype of Depression Affecting 1 in 4 Patients

Researchers at the University of Sydney analyzed data from 11,380 participants in the Australian Genetics of Depression Study and identified a proposed depression subtype linked to disrupted body clocks. The “circadian” pattern reflects a mismatch between a person’s internal rhythms and the day-night cycle, described as feeling persistently jet-lagged. The researchers identified it through six features: symptoms that vary by season, later-than-average sleep timing, a large difference between sleep schedules on workdays and free days, an evening preference, a tendency to sleep longer when possible, and pronounced morning tiredness. About one in four participants met the criteria. Although the subtype overlapped most with atypical depression, many people with atypical depression did not fit the circadian profile, suggesting the categories are not identical.

Participants in the circadian group tended to experience depression earlier and reported more severe features, including mania, psychosis, and suicidal thoughts. They were also more likely to gain weight during depressive episodes, carry elevated genetic risks related to conditions such as ADHD, and have inflammatory or cardiovascular health problems. Common antidepressants were less likely to help them and more likely to cause side effects. The researchers argue that treating depression as a single disorder may overlook distinct biological drivers and contribute to ineffective care. Because this subtype appears connected to body-clock disruption, they suggest clinicians consider circadian-focused approaches, including light therapy and melatonin, earlier for people with this pattern.