A person's sleep habits may help identify a newly proposed subtype of depression linked to the body's internal clock.In a study of 11,380 Australian adults with a history of depression, about 23% met researchers' criteria for what they called "circadian depression."The profile included at least three of six features: being an evening person, waking up feeling very tired, sleeping longer during the worst periods of depression, experiencing seasonal changes, having a later midpoint between falling asleep and waking up, and experiencing "social jetlag," a large shift in sleep timing between workdays and days off.The seasonal changes could involve sleep, mood,
