Sleep habits could offer clues to a hidden type of depression, scientists say

A person's sleep habits may help identify a newly proposed subtype of depression linked to the body's internal clock, researchers say. The profile, which they call 'circadian depression,' is tied to disruptions in sleep-wake rhythms, and the researchers say recognising it could open the way to more personalised care for people living with depression.

The study was led by researchers at the University of Sydney and the QIMR Berghofer Medical Research Institute in Australia, with co-authors from institutions in Australia, the United Kingdom and the United States. It included 11,380 Australian adults with a history of depression.

About 23 percent of the participants met the researchers' criteria for the proposed subtype. The profile was built from the sleep habits and internal-clock features those participants shared.

The researchers used a list of six features, and a person needed at least three of them to fit the profile. The features are: 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, activity, appetite, weight or energy, the study noted.

The study was published on October 20 in The British Journal of Psychiatry. The researchers said the findings could eventually help guide more personalised care for patients with depression.

First author Emiliana Tonini, Ph.D., from the University of Sydney's Brain and Mind Centre, said: 'Depression is not a uniform illness, and understanding the characteristics of different subtypes means we can give people earlier access to treatments that will be most effective for them.' The researchers were clear, however, that the label is not a formal diagnosis. It needs independent replication and further study, they noted.

The study found that people in the circadian group reported an earlier onset of depression and more severe symptoms than those who did not meet the criteria. They were also more likely to report weight gain during depressive episodes.

Differences also showed up in medication. Participants in this group reported poorer responses and more side effects with two common classes of antidepressants, selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs). Participants reported how well their medications worked, but the study did not explain why some were less effective, and it did not test treatments aimed at adjusting the body's internal clock.

Study co-author Dr. Ian Hickie, a professor of psychiatry at the University of Sydney, said the proposed profile 'cuts across existing historic subtypes' of depression. He said it most closely overlaps with atypical and bipolar depression, because they share features such as low energy and oversleeping.

Atypical depression can also involve weight gain, while bipolar depression refers to depressive episodes in people with bipolar disorder, which also involves periods of unusually elevated or irritable mood and increased energy. 'We define circadian only by sleep-wake and circadian features,' Hickie said.

For some people with this profile, Hickie said sleep-wake disruption may be more than a symptom of depression. It may be the underlying cause. The study itself, however, could not establish whether body-clock disruption caused depression or resulted from it.

The researchers cautioned that staying up late or struggling to wake up does not, by itself, mean someone has depression. Participants had already reported depression, which in some cases was severe, recurring or long-lasting. The researchers acknowledged several limitations. Participants reported their own sleep patterns and treatment experiences, and the cross-sectional analysis did not show whether sleep disruption preceded or followed depressive symptoms. All participants were of European ancestry, so the findings may not apply to other populations.

Participants in the circadian group also reported more manic-like experiences. John Puls, a psychotherapist and adjunct professor at Florida Atlantic University who was not involved in the study, said those symptoms could help explain their reported response to antidepressants. In his words: 'SSRIs are not meant to treat these more significant mental health symptoms that go far beyond depressive symptoms. In fact, some SSRIs can actually worsen manic symptoms, which lead to poor sleep.'

Jillian Amodio, a Maryland-based psychotherapist and founder of Moms For Mental Health who was not involved in the research, cautioned against using the findings as 'a benchmark for treating each person in the same way.' She said biological, environmental, social and psychological factors all need to be accounted for, and researchers should examine more populations, including people who work night shifts, and account for differences in time zones and seasons.

The researchers said light exposure, regular sleep schedules and melatonin-related approaches warrant further study. They hope that identifying depression subtypes through sleep-rhythm features will eventually allow patients to receive more precise, personalised treatment.