Sleep patterns may help researchers identify a possible subtype of depression tied to the body’s internal clock, according to a study of Australian adults.
Among 11,380 participants with a history of depression, about 23% met the researchers’ criteria for what they termed “circadian depression.” To fit the profile, people had to report at least three of six traits: being more alert in the evening, waking feeling very tired, sleeping longer during their most difficult depressive periods, experiencing seasonal changes, having a later midpoint to their sleep, or shifting their sleep schedule substantially between workdays and days off.
Seasonal changes could affect sleep, mood, activity, appetite, weight or energy. The findings, published Oct. 20 in The British Journal of Psychiatry, may eventually help clinicians tailor depression care, the researchers said. For now, though, circadian depression is a proposed label, not a formal diagnosis, and the results need to be replicated independently.
People who fit the profile reported that their depression began earlier and was more severe than that of other participants. They were also more likely to say they gained weight during depressive episodes.
They described less benefit and more side effects from two commonly used types of antidepressants: selective serotonin reuptake inhibitors, or SSRIs, and serotonin-norepinephrine reuptake inhibitors, known as SNRIs. The study relied on participants’ accounts of how well their medication worked. It did not determine why some treatments seemed less effective, or test therapies intended to reset the body clock.
Researchers said approaches involving light exposure, consistent sleep schedules and melatonin deserve further study. Co-author Ian Hickie, a University of Sydney psychiatry professor, said the proposed profile overlaps with features of existing depression categories, including atypical and bipolar depression. Those conditions can involve low energy and oversleeping. Atypical depression may also involve weight gain, while bipolar disorder includes depressive episodes as well as periods of unusually elevated or irritable mood and increased energy.
Hickie said the proposed category is based specifically on sleep-wake and circadian features. For some people, disruption to the sleep-wake cycle may not simply accompany depression; it could contribute to it. But this study cannot show whether body-clock disruption causes depression or follows from it.
Staying up late or struggling to wake up does not, on its own, mean someone is depressed. Everyone in the study had reported a history of depression, which for some participants was severe, recurring or long-lasting.
People in the circadian group also reported more experiences resembling mania. Psychotherapist John Puls, who was not involved in the research, said those symptoms might help explain why participants reported poorer responses to antidepressants. He noted that SSRIs are not designed to treat manic symptoms and, in some cases, may worsen them, potentially affecting sleep.
The study had several important limitations. Participants described their own sleep habits and treatment experiences, and the one-time analysis could not establish whether sleep problems came before or after depressive symptoms. All participants were of European ancestry, which means the findings may not apply to other groups.
Psychotherapist Jillian Amodio, who was also not involved, cautioned against treating the proposed profile as a one-size-fits-all guide. Biological, environmental, social and psychological factors all matter, she said. Further research should include a wider range of populations, including night-shift workers, and account for differences in time zones and seasons.
The study was led by researchers at the University of Sydney and QIMR Berghofer Medical Research Institute, with collaborators from institutions in Australia, the United Kingdom and the United States.
