In some people with depression, sleep and the biological clock seem to play a particularly important role.
Our bodies have an internal clock that roughly follows the rhythm of the day. It helps us know when to sleep, wake up or be active. But this rhythm does not work the same way for everyone. Australian researchers wanted to find out whether disruptions to it could characterize certain cases of depression.
A link between circadian rhythm and depression.
They analyzed the responses of 11,380 people who had experienced depression, often severe or recurrent. To identify disruptions in daily rhythms, they examined six signs, including sleeping for a very long time, feeling exhausted in the morning, being more active in the evening or seeing one's mood vary with the seasons.
The researchers then brought together the people showing at least three of these signs. They identified 2,604 of them, or 23% of the participants. This group corresponds to what they propose calling “circadian” depression, referring to the biological rhythm that organizes our days.
Among these participants, depression had generally begun earlier and was accompanied by more pronounced symptoms. They also reported that some common antidepressants, particularly those that act on serotonin, had worked less well for them. The reported side effects were also more numerous.
The research team wanted to identify other clues in their DNA. They found more genetic characteristics associated with a preference for later schedules, as well as with certain mood and sleep disorders. These results support the idea of a biological link, without making it possible to explain precisely how it works.
Does this mean that a shifted sleep schedule causes depression? No. The study compares people at a given point in time, mainly based on their own reports. It does not demonstrate that their internal clock is the cause of their symptoms. And the 23% observed cannot be applied to all people with depression.
The researchers nevertheless hope that this distinction will one day help in choosing more suitable treatments. They notably mention treatments that act on sleep-wake rhythms, such as light therapy. But the study did not test their effectiveness in this group: further research will be needed to determine whether they actually provide a benefit.
For now, this profile therefore remains a scientific proposal, not an officially established diagnosis. Other teams will have to verify these results in different populations, then determine whether knowing a patient's biological rhythm can actually lead to better treatment.