With one in six U.S. adults suffering from some form of mental illness and 10-18% of adults living with a chronic sleep problem, understanding the causal factors involved in the two groups of disorders and the interplay between them is no small issue.
It’s been known for years that those with mental issues are at a much greater risk for sleep disorders than those without. While about one in five Americans suffers from some sort of chronic sleep disorder, four out of five Americans with mental health issues have an accompanying sleep issue.
- Somewhere between 65% to 90% of adults with depression suffer from a sleep disorder.
- The most common sleep disorder among those with depression is insomnia, but 20% suffer from (the more easily treated) sleep apnea.
- For adults with anxiety disorder, 50% also suffer from a sleep disorder.
- Those with bipolar disorder are plagued with sleep disorders at a rate anywhere between 69-99%.
- About 25-50% of children with ADHD suffer from a sleep disorder.
Unsurprisingly, the most common sleep ailments here are insomnia and hypersomnia (sleeping excessively) during manic and depressive phases respectively.
While not all with mental health issues present a sleep disorder, it’s clear that a great many do.
Now that we’ve established a strong basic link between the two issues, let’s delve into the synergy between them and think about the methodology used to determine this link.
How do we determine that sleep disorders can cause or exacerbate mental illness?
There are a few ways to try and figure this out.
One approach is to identify people presenting sleep disorders with no evidence of mental health issues as determined by testing and follow them over time. While a robust approach, it does leave to question whether the same genetic, lifestyle or psychological factors that could cause sleep issues may also play a role in depression that tends to manifest itself at a later date than the sleep disorder (see lurking variable).
This study from the Henry Ford Health Sciences Center makes use of this type of experimental design and serves as much of the basis for what we know about sleep disorders potentially leading to mental health issues.
Additionally, to see if sleep disorders can worsen mental illnesses, we need to see if treating a sleep disorder (but not necessarily psychiatric issues) helps to improve the psychiatric issue. This may hint that sleep disorders can be a cause of mental illness. However, due to the structure, we can only say with certainty that the presence or severity of sleep disorders can affect the severity of mental health issues.
A study from Oxford has provided some of the most compelling research on the intersection between mental health and sleep using a form of the above methodology.
These studies are difficult to get right, and there are some things we should keep in mind when discussing them.
Inherent difficulties in establishing causal relationships between sleep disorders and mental health
Let’s say, hypothetically, that someone ruins their knees after years of physical activity.
They can no longer exercise and as a result, begin to suffer from sleeplessness early on. Because they can no longer exercise, they find themselves feeling less fulfilled or they gain weight, later showing signs of depression.
The knee injury preventing exercise causes first insomnia and then depression — making it appear that one causes the other whereas the injury caused both, just at different times.
One single factor that affects two different variables (independent and dependent) but isn’t controlled for in studies is called a lurking or confounding variable — something that is important to keep in mind in these chicken vs. egg questions.
Establishing the chicken and egg relationship
I can hear you screaming to get to the point, so here we go.
Depression appears to be the mental illness with the most evidence that suggests it may be caused or exacerbated by sleep disorders.
Let’s focus on this in particular.
EVIDENCE SUGGESTING SLEEP DISORDERS, SUCH AS INSOMNIA, CAUSE DEPRESSION
In the Henry Ford Health Sciences Center study, young adults were brought in for an initial interview that included questions on sleep and mental health issues and returned again three years later to follow up.
The research showed that individuals who in the initial interview reported episodes of insomnia but no signs of major depression were four times as likely to develop major depression by their second interview three years later.
A more recent study, also done by the Henry Ford Health Sciences Center, employed a very similar experimental design and presented similar results. The team discovered that those expressing insomnia or insomnia-like sleep issues were again at a significantly greater risk of developing a major depressive disorder than those without sleep issues. This study specifically controlled for stressor events, age, and gender, making it extremely strong evidence for sleep disorders as a cause for depression.
Let’s throw some more evidence into the pile. Researchers in a long-term study on twins discovered that while sleep problems at age eight were a statistically significant predictor of depression by age ten, the opposite relationship was not true.
Even if we want to put our cynical hats on and reintroduce the idea of lurking variables or lack of controls into thinking about this, these studies paint a pretty clear picture that insomnia and depression have a strong causal link. While the possibility of lurking variables in this research is present, the case for insomnia as a cause or sign of major depression is becoming very compelling.
EVIDENCE SUGGESTING SLEEP DISORDERS LIKE INSOMNIA EXACERBATE DEPRESSION AND COMPLICATE TREATMENT OF DEPRESSION
The studies on insomnia exacerbating (but not explicitly causing) depression are extremely robust as well. The aforementioned Oxford study focused on treating students presenting mental health and sleep issues for only their sleep issues through something called Cognitive Behavioral Therapy or CBT.
Though CBT intervention focused on insomnia treatment, researchers found that as insomnia symptoms decreased, so too did psychiatric symptoms like hallucinations, paranoia, and depression.
It’s also been reported that depressive individuals respond worse to treatment if they present sleep disruptions than those without, and that individuals with treated depression were more prone to relapse if they have untreated sleep disorders.
Additionally, other studies have shown that those unlucky enough to suffer both depression and insomnia as opposed to simply depression rank much higher in terms of suicidal behavior.
So can we conclude with absolute certainty that insomnia can cause depression?
Not just yet.
Let’s approach this with some level-headedness and scientific literacy.
While it appears that insomnia often precedes depression, and while treating the symptoms of insomnia can ameliorate the symptoms of depression or other mental illnesses, the studies aren’t ironclad and robust enough to come to a conclusion.
We’re close, but until we see more detailed and long-term studies, or research elucidating the biochemical or genetic foundations behind depression or insomnia, we can’t with 100% confidence conclude that sleep disorders like insomnia cause mental illness such as depression.
WHERE DOES THIS LEAVE US?
What we can take away from this is that we can use insomnia and other sleep disturbances as a probable early marker of depression and other mental illness, and can begin preventative or treatment steps before these mental disorders set in.
Parents who notice their children have significant sleep difficulties may want to take them in to see a mental health specialist. If you find yourself up all hours of the night, you may want to speak to a doctor about treating your sleep issues. In addition, getting information on identifying and preventing the onset of major depressive disorder symptoms could be helpful early on.
The presence of a sleep disorder could be an important red flag that something might be going wrong with your body or brain chemistry. Pay attention to it.
While research hasn’t yielded an “aha!” moment on the subject yet, we’re heading in the right direction. We’ve gotten that much closer to determining that mental illness may be developed through sleep disorders.
Some more useful information: