Emerging scientific research clearly shows that the relationships between depression and insomnia are far more complex than originally understood. The current model as expressed in the psychiatric terminology of the DSM-IV-TR (the diagnostic manual used by psychiatrists and psychologists to define mental health disorders) emphasizes insomnia as a common symptom of depression. Some patients with depression show the symptom of hypersomnia (sleeping too much), but most depressed patients who report sleep problems emphasize insomnia over hypersomnia.
The newer model emerging from a sleep medicine perspective indicates a much more bi-directional relationship between insomnia and depression. In many instances, the insomnia may occur first, which then seems to lead to the depression. Above all, what's most important from the research of others and the research and clinical experience of our centers is that insomnia takes on a life of its own among depressed patients.
When we say "a life of its own," we mean that insomnia is no longer just a symptom of depression. It is a co-occurring sleep disorder that is aggravating the depression condition. This critical distinction, therefore, means that it is imperative to treat the insomnia instead of waiting around to see what happens to the insomnia when the depression is treated.
Some evidence already points to the potential to improve depression simply by treating the insomnia. Other evidence suggests that treating insomnia early might prevent depression from developing or might lessen the depression that still develops.
Last, our experience tells us that even this degree of complexity is insufficient to explain the full relationship between insomnia and depression. We believe that an enormously large number of patients with both depression and insomnia also suffer from sleep-disordered breathing (SDB). We also believe that SDB goes largely unnoticed, undetected, and undiagnosed in these patients and therefore it obviously goes untreated.
The bottom line is that if SDB persists in a patient with insomnia and depression, then we would expect this patient to have difficulty fully resolving either the insomnia or depression, and usually both. Clinically, we think that any depressed patient with insomnia who is not responding well to antidepressants would be well served by completing an overnight sleep test to check for SDB.