Medically reviewed by
Dacelin St Martin, MD
Triple board-certified in Sleep Medicine,
Internal Medicine, and Pediatrics.
Causes | Epidemiology | Symptoms | Risk factors | Diagnosis | Treatment
Sufficient sleep is necessary to maintain optimal physical health, cognition, and mental health.
The American Academy of Sleep Medicine and the Sleep Research Society define optimal sleep as greater than seven hours of sleep for those ages 18 to 60 years, while the National Sleep Foundation recommends that those aged 18-64 get seven to nine hours of sleep per night and those over 65 get seven to eight hours.
Compared to optimal sleep durations, both short (<6 hours) and long sleep (>8 hours) durations are associated with an increased risk of depression.
Up to 90 percent of those with depression also report sleep disturbances.
Suboptimal sleep affects the risk of depression, and depression itself can further result in disruption of REM sleep and other sleep disturbances,[4,5] exacerbating the effects of inadequate sleep.
The relationship between sleep and depression is bidirectional. There’s a clinical correlation between inadequate sleep and an increased incidence of depression; however, the causal relationship between these two factors is influenced by various physiological imbalances.
Disruption of the circadian rhythm through chronic insufficient sleep affects the autonomic nervous system, neuroendocrine stress system, and a patient’s stress response.
Disruption of the circadian rhythm results in imbalances in the production and secretion of the neurotransmitter serotonin, increasing susceptibility to depression.
Sleep disturbances can have a variety of causes. Obstructive sleep apnea (OSA), characterized by sporadic airflow disruptions during sleep, can disrupt sleep and is correlated with a heightened risk of depression.
Patients with OSA, restless legs syndrome (RLS), and periodic limb movement disorder (PLMD) all have a greater likelihood of experiencing depressive symptoms.
Alternately, depression can lead to disrupted sleep. The most common comorbid sleep condition for depression is insomnia, occurring in approximately 75 percent of patients presenting with depression. Excessive sleep (e.g., hypersomnia) also correlates with an increased risk of depression.
Additionally, medications to treat other conditions, such as stimulants, opioids, glucocorticoids, and some antidepressants, may affect sleep quality and thus be the underlying cause of or contributing factor for sleep disturbance and depressive symptoms. Behavioral factors and sleep hygiene also will affect sleeplessness and depression.
One epidemiological study demonstrated that insomniacs were 9.82 and 17.35 times more likely to have depression and anxiety, respectively.
This study also revealed that African Americans have a heightened risk for comorbid depression and anxiety than Caucasian participants, and depression was more common in women than men.
With comorbid insomnia and depression, it is more likely that a patient will present with chronic insomnia than acute insomnia.
Chronic insomnia is defined as three or more episodes of insomnia per week for at least three consecutive months. Symptoms of depression include:
- Chronic and persistent depressed mood
- Loss of interest in daily activities
- Greater than 5% change in weight in a single month
- Insomnia or hypersomnia
- Feelings of worthlessness or hopelessness
- Thoughts of suicide or self-harm
- Decreased ability to concentrate
- Impairment in psychomotor function 
Many studies have demonstrated that insomnia is a significant risk factor for major depressive disorder (MDD). Insomnia also correlates with worse outcomes for those with MDD.
Risk factors for insomnia include advanced age, night shift work, chronic pain conditions, such as fibromyalgia, medications, and mental illness.[16,18]
As with depression, insomnia is also more common in women than men. In addition to depression, insomnia is a risk factor for other comorbidities, including additional mental illnesses and cardiovascular disease.[16, 18, 20]
Both depression and insomnia are diagnosed based on patient history and self-reported symptoms.
An insomnia diagnosis is established based on an evaluation of sleep history, the incidence of psychiatric conditions, and medications prescribed.
Additionally, using a sleep diary for the most accurate recollection of sleep quality can be valuable in an insomnia diagnosis.
Depression is defined as a state of prolonged mood states, such as sadness, anxiety, despair, or emptiness that interfere with daily function.
Depression is often marked by extreme fatigue, insomnia or hypersomnia, a depressed mood throughout the day, extreme fluctuations in weight, decreased ability to concentrate, and recurrent thoughts of self-harm or suicide.
Providers can utilize screening questionnaires for diagnosis, as well as monitoring symptoms associated with depression. The patient Health Questionnaire-Nine Item, or PHQ-9, is the most used questionnaire. As the name implies, it consists of nine questions used to track depression symptoms, which correspond to the nine criteria outlined by the DSM-5 for a diagnosis of unipolar depression.
Each item is given a value from 0 to 3 and the total score aids providers in diagnoses and disease monitoring. PHQ-9 items include:
- Little interest or pleasure in doing things
- Felling down, depressed, or hopeless
- Trouble falling or staying asleep, or sleeping too much
- Feeling tired or having little energy
- Poor appetite or overeating
- Feeling bad about oneself, feeling like a failure
- Trouble concentrating
- Moving or speaking so slowly that other people have noticed, or the opposite, being fidgety or restless
- Thoughts of suicide, or of hurting oneself
In specific instances to monitor poor sleep, the use of polysomnography (PSG) is used. A PSG may be warranted when a sleep disorder is suspected to be the primary disorder causing the depression. Additionally, chronic insomnia that is refractory to standard treatments may require a PSG.
Treating sleep disruption has been shown to provide benefits to depressive symptoms. Because patients with OSA, RLS, and PLMD have an increased incidence of depression, strategies to address these sleep disturbances can also alleviate symptoms of depression.[6, 10, 23]
Further, treatment of depression with antidepressants correlates with improved sleep quality.
However, there is some evidence that selective serotonin reuptake inhibitors (SSRIs) are less effective at simultaneously combatting sleep disruptions than previously utilized tricyclic antidepressants.[23, 24]
Cognitive-behavioral therapy (CBT) is empirically shown to be an effective non-pharmacological method for treating both depression and sleep disturbances.
Because of the bidirectional link between these two conditions, treatment of either condition will improve symptoms for patients. However, healthcare providers may alter the way they manage insomnia or other sleep disorders in patients with comorbid depression as compared to those experiencing sleep disturbances without depression.
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