Daytime sleepiness and troubled sleep at night are hallmark symptoms of clinical depression. So is hypersomnia. Not all depressed people have sleep disorders, but many do and when evaluating patients for depression, doctors ask about sleep patterns.
EEG tests of depressed patients show they have a longer sleep latency, shortened time in slow-wave sleep, shift of REM sleep to earlier in the night, and sleep maintenance insomnia (they wake up during the night).
The cause-and-effect runs both ways. Don’t get enough sleep and you increase your chances of depression and other mental illnesses. Depression causes insomnia and hypersomnia. It is estimated that 60% of people who meet the criteria for major depressive disorder also experience insomnia and mention it to their doctors or therapists - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3056174/ It is also estimated that 10-20% of diagnosed insomniacs also have clinical depression. The two disorders are often co-morbid. An article in the Journal Sleep reported that children with sleep disturbances (both insomnia and hypersomnia) were more likely to be depressed. Further, effective treatment of depression often improves sleep duration and quality.
Especially in young adults, there is a strong correlation between insomnia and major depressive disorder. Genes involved in the molecular clock and circadian cycle are known to be involved with bipolar disorder, although nobody exactly knows how. When scientists examine mice with mutations in the so-called CLOCK gene (important in the circadian cycle), they find the mice act like humans with mania. When the mice are given lithium (a treatment for bipolar disorder), their behavior reverts to normal. So it appears that this important part of the sleep control cycle is tied up with mood and mood disorders.
It is easy to think of reasons why insomnia might lead to depression: it is unpleasant, the subject lies awake at night and can ruminate on unpleasant thoughts, daytime sleepiness reduces general quality of life.
And the still not-well understood neurochemical bases for depression and sleep disorders are almost certainly linked. Corticotropin-releasing factor (CRF) is a neuropeptide and is found in elevated levels in people with depression and anxiety disorders. It also is found in high levels in many insomniacs. The hypothalamic-pituitary-adrenal (HPA) axis is stimulated perhaps excessively in both depressed people and insomniacs.
The large majority of psychiatric illnesses can induce sleep disorders (or the other way around), and insufficient sleep is a risk factor for making most of them worse. Sleep deprived people also have stronger emotional reactions in general. Brain scans of healthy people subjected to sleep deprivation show increased activity in one part of the brain (the amygdala) known to be involved in emotional response when the people were shown pictures of disturbing images. And the lack of sleep experienced by new mothers may be a contributing factor in post-partum depression.
Sociologists have also found that loneliness is associated with fragmented sleep.
WebMD reports that 15% of patients with depression have hypersomnia and 80% have insomnia. Whether it is insomnia or hypersomnia, depressed people usually report unrefreshing sleep. Sleep is less fun when you are depressed.
Indeed, in people with no history of depression, insomnia is correlated with future onset of depression. Those with insomnia are twice as likely to become depressed as those without.
People with apnea are more likely to suffer from depression, and even people without true apnea, but who snore, are more likely to be depressed. This relationship is particularly strong in men. (http://www.nytimes.com/2012/04/03/health/research/less-severe-sleep-disorders-also-raise-depression-risk.html)
"The best bridge between despair and hope is a good night's sleep." ~E. Joseph Cossman
Although both depression and insomnia can be treated without drugs, there are pharmacological interventions for both, and not coincidentally, both can be addressed with anti-depressants. The most common anti-depressant medications today belong to the class called selective serotonin reuptake inhibitors, and insomniacs who start taking one of those drugs often find relief for their sleeping problems. Non-pharmaceutical methods of addressing insomnia can also help with depression.
About 15% of depressed people have hypersomnia rather than insomnia. The pharmacological treatment for idiopathic hypersomnia is usually a stimulant – something that works opposite of sleeping pills. That’s why it is important for doctors to evaluate whether long-sleeping patients might have depression and be a better candidate for anti-depressant medication.
It is no coincidence that pharmaceutical companies developing melatonin receptor agonists have both the insomnia market and the depression market in their sights.
REM (rapid eye movement) sleep abnormalities result in brain activity patterns similar to those seen in depression. Indeed, during REM parts of the brain exhibit similar electrical activity to that in depressed people. And depressed people have their first REM session earlier in the night than non-depressed people. The worse the depression, the earlier the REM, and in bad cases the sequence of sleep stages is upset and the first REM period happens before the first deep sleep period. Given the importance of this first deep sleep period to growth hormone and the body's maintenance, this pattern is particularly detrimental.
This leads to the hypothesis that suppression of REM could help treat depression. And indeed, common antidepressant drugs do tend to suppress REM, although that is not what the drug makers had in mind when they designed the drugs. No drug eliminates REM, and it would be very risky to try to do so, given that REM is a section part of sleep, even if the reasons for it and functions it serves are not completely understood.
Scientists have found that patients with major depressive disorder have high activity in the ventromedial prefrontal cortex (vmPFC) coupled with low activity in dorsolateral prefrontal cortex section of the brain. (http://www.psychologytoday.com/blog/dream-catcher/201107/sleep-and-depression). Scientists are working out the details, but this may provide a clue to why REM activity increases in depressed patients.
Sleep researcher Rosalind D. Cartwright notes that most hypotheses about dreaming emphasize moods and emotions and that "negative mood is down-regulated" during sleep. As a bright new day dawns, people are generally more upbeat and in a better mood.
Related: stress and sleep problems.