Though insomnia is often viewed as being an unfortunate accompaniment to depression, research indicates that perhaps this sleep disorder represents a healthy response to an otherwise off-kilter body chemistry. This supposed link between insomnia and depression is the serotonergic system—the body’s system for recognizing the neurotransmitter serotonin. If this is the case, this new perspective might open up new avenues to treat depression and sleep disorders.
Depression and disturbances to healthy sleeping often go hand-in-hand. Over 70 percent of depressed patients complain of insomnia, while a smaller percent complain of hypersomnia (excessive sleepiness, particularly in the daytime). According to electroencephalogram (EEG) studies, once asleep, a depressed person is more likely to wake up too early or in the middle of the night. Depressed patients are also likely to experience longer periods of rapid eye movement sleep (REM sleep), particularly during their first sleep cycle.
Is it just a coincidence that people with clinical depression also tend to suffer from sleep disorders? A significant body of evidence indicates that the answer to this question is a resounding “no.” In particular researchers have indicated that both sleep and depression are greatly influenced by the serotonergic system—the parts of the body that are sensitive to the neurotransmitter serotonin. With regards to depression, abnormalities in the production of serotonin, a lack of receptors for serotonin, or shortages in the necessary building blocks of serotonin have all been considered as contributing factors for the development of depression.
Sleep is also greatly affected by changes in serotonin levels. In general the serotonergic system is most active during the waking hours, and peters out to a minimum activity level during normal, healthy sleep. In particular, in order to fall into REM sleep a person must rely on an overall decrease in the sensitivity to serotonin (aka the serotonergic tone) in the structures of the brain stem. People with an increased serotonergic tone, such as those taking some forms of antidepressants, therefore will have greater difficulty falling into REM sleep.
The link between depression and sleep deprivation was elegantly demonstrated in a series of studies in which patients reported feeling significant mood improvements after a full night of sleep deprivation. Paradoxical though this may seem, experts have noted that this makes sense when one considers the neurochemistry at hand. If depression is characterized by a deficit in serotonin, then one might predict that a short-term solution for alieving this deficit would be to stay awake and thereby keep serotonin levels high by forestalling the normal serotonin depletions that happen during slumber. Further investigation has also found that sleep deprivation causes serotonergic neurons to activate, not unlike some antidepressant medications.
With this link in mind, author Joëlle Adrien proposed that insomnia might be a body’s healthy response to try and compensate for the serotonin deficits associated with depression. This view is a subtle but an importantly distinct divergence from the more wide-spread belief that insomnia is a symptom or contributing factor to depression. While certainly a lack of sleep will in the long-term impose further complications on a person’s health, it is possible to see how a distressed body might be disposed towards the immediate benefits of a quick serotonin fix. Such an understanding might help researchers better engineer and understand antidepressants, as well as identify people at risk for either condition.
By Sarah Takushi