What Is the Biology of Insomnia?

Insomnia is a common sleep disorder characterized by difficulty falling asleep that can last for days or weeks (short-term insomnia) or for more than 6 months (chronic insomnia). Insomnia can be caused by biological factors such as anxiety, depression, sleep apnoea, genetics, and chronic conditions.

It can also be caused by environmental factors such as sleeping habits, the safety of the place where you sleep, and the comfort of the bedding and the room where you sleep.

Corresponding to the statistics of the American Sleep Association (ASA), approximately 30% of adults experience short-term insomnia, while 10% of adults suffer chronic insomnia [1]. In the United Kingdom, approximately 50% of adults complain of short-term insomnia, while 10-15% suffer from chronic insomnia [2].

Why Do We Need Sleep?

Sleep is essential to our biological metabolism and for the proper functioning of our nervous system. For instance, insomnia can significantly affect protein metabolism necessary for the function of cells, tissue, and organs. It can also lead to cognitive disorders (e.g., effect on learning and memory), and mood swings.

How Is Sleep Controlled?

Sleep is controlled by the brain through the suprachiasmatic nucleus of the hypothalamus. The sleep pattern occurs through repetition of a cycle that comprises 5 phases measured by electroencephalography (ECG) [3]:

  • Phase 1: light sleep phase characterized by slow eyes’ movement and muscle relaxation.
  • Phase 2: this phase is characterized by the cessation of eyes’ movement and the slowdown of the brain waves such as the electrical pulses associated with wakefulness.
  • Phase 3: beginning of deep sleep delta waves. At this stage, the delta waves are interrupted by faster and smaller waves.
  • Phase 4: characterized uninterrupted delta waves leading to deep sleep.
  • Rapid Eye Movement (REM): this phase is characterized by rapid eye movements, rise in heart and blood pressure, and dreaming.

Most adults require 7-9 hours’ sleep, while teenagers need 9 hours’ sleep and infants typically sleep for about 16 hours. However, biological, and environmental factors can alter the length and quality of sleep leading to insomnia.

What Are the Biological Causes of Insomnia?

1- Chronic Disease Conditions

Any chronic condition that causes pain can have dramatic effects on sleep. For instance, Rheumatoid arthritis can lead to shorter sleep times and fragmented sleep, resulting in a poor sleep quality that feeds back into a heightening sensitivity to pain, creating a vicious cycle [4].

2- Genetic Factors

Using the genome-wide association study (GWAS) and a genome-wide gene-based association study (GWGAS) in 113,006 individuals, a study identified 3 loci (location of genes on chromosomes) and 7 genes that are associated with insomnia. Among these, a strong association between the developmental gene MEIS1 and insomnia was reported for both males and females [5].

3- Breathing-Associated Conditions

Conditions that prevent proper breathing such as sleep apnoea, asthma, congestive heart failure, and chronic obstructive pulmonary diseases, can all lead to insomnia. Breathing difficulties result in frequent wakening, shorter sleep times, and fragmented sleep, which lead to poor sleep quality.

4- Urinary Conditions

Conditions such as an enlarged prostate and urinary tract infection result in frequent urination at night (Nocturia) that affects sleep quality.

5- Mental Health Disorders

  • Anxiety and Depression:

Anxiety and Depression are mental states characterized by psychological symptoms such as low mood and self-esteem, irritability and intolerance to others, difficulty in making decisions, and suicidal thoughts.

A study that analyzed the link between depression and insomnia in 7954 respondents who were questioned about sleep complaints and psychiatric symptoms, found that the risk of developing new major depression was much higher in those who had insomnia at both interviews compared with those without insomnia [6]

  • Post-Traumatic Stress Disorder (PTSD)

One of the main characteristics of PTSD is nightmares that relate to previous traumatic events. Nightmares can disrupt sleep, and their repetitive frequency can create a fear of falling asleep [7].

  • Chronic Fatigue Syndrome

Insomnia can be caused by chronic fatigue syndrome, an illness characterized by profound disabling tiredness, a diminished capacity to perform routine tasks and sleep disruption that lasts for more than 6 months.

  • Headaches and Migraines

A Headache is a symptom of continuous pain in the head, face, or neck that can last from 30 minutes to several hours, while a migraine is a severe form of headache that manifest as an excruciating pain on one side of the head accompanied by a feeling of sickness and an increased sensitivity to light and sound. Pain from headaches and migraines can significantly affect the quality of sleep.

6- Medication

Medications such as diuretics, some steroids (e.g., prednisone), decongestants, beta-blockers, asthma medications (e.g., theophylline) can lead to short-term or long-term insomnia depending on the duration of the treatments. For instance, diuretics can increase the frequency of urination, while prednisone can cause headaches, stomach pain, and sleep disruptions.

7- Stimulants

Caffeine, nicotine, and other central nervous system stimulants increase alertness which prevents the willingness of going to sleep.

8- Restless Legs Syndrome

Restless Legs Syndrome is the urge to move legs due to unpleasant sensations, such as tingling and aching, and that is relieved by movement. This condition can result in sleepless nights, and therefore, contributes to insomnia.

10- Dementia

The sleep hormone melatonin is essential in the synchronization of the circadian rhythms, and in ensuring the quality of sleep. In dementia individuals, melatonin secretion is low or dysregulated which affects sleep and leads to insomnia [8].

What Are the Environmental Causes?

Environmental factors such as the comfort of the bedding and the room where you sleep, are essential for quality sleep. For instance, if the bed is uncomfortable or if your partner is snoring, or your surrounding is noisy, the quality of your sleep will be affected.

What Is the Treatment for Insomnia?

Depending on the causes of insomnia, treatment can include lifestyles changes that promote quality of sleep or cognitive behavioral therapy (OBT). Lifestyle changes can involve improving the quality of the bedding, the room where you sleep, consuming less coffee and nicotine-associated products, and exercising.

Cognitive-behavioral therapy can help improve sleep patterns through the introduction of changes in behaviors and thoughts that interfere with sleep such as maintaining a consistent sleep schedule. For insomnia that is caused by anxiety, depression, and chronic fatigue syndrome, cognitive behavioral therapy can help improve cognitive disorders, behaviors, and develop coping strategies that can also help with sleep.


Insomnia is a serious condition that can have severe repercussions on daily life. If untreated insomnia can lead to mental health problems such as anxiety and depression. Although most of the causes can be prevented through changing lifestyle and environmental factors, some are associated with genetics, aging, and neurodegenerative diseases that require more advanced medical treatments.



[2] Morphy, H., Dunn, K.M., Lewis, M., Boardman, H.F. and Croft, P.R., 2007. Epidemiology of insomnia: a longitudinal study in a UK population. Sleep30(3), pp.274-280.

[3] Brown, R.E., Basheer, R., McKenna, J.T., Strecker, R.E. and McCarley, R.W., 2012. Control of sleep and wakefulness. Physiological reviews.

[4] Ohayon, M.M., 2005. Relationship between chronic painful physical condition and insomnia. Journal of psychiatric research39(2), pp.151-159.

[5] Hammerschlag, A.R., Stringer, S., De Leeuw, C.A., Sniekers, S., Taskesen, E., Watanabe, K., Blanken, T.F., Dekker, K., Te Lindert, B.H., Wassing, R. and Jonsdottir, I., 2017. Genome-wide association analysis of insomnia complaints identifies risk genes and genetic overlap with psychiatric and metabolic traits. Nature genetics49(11), pp.1584-1592.

[6] Ford, D.E. and Kamerow, D.B., 1989. Epidemiologic study of sleep disturbances and psychiatric disorders: an opportunity for prevention?. Jama262(11), pp.1479-1484.

[7] Maher, M.J., Rego, S.A. and Asnis, G.M., 2006. Sleep disturbances in patients with post-traumatic stress disorder: epidemiology, impact and approaches to management. CNS drugs20(7), pp.567-591.

[8] Liu, R.Y., Zhou, J.N., van Heerikhuize, J., Hofman, M.A. and Swaab, D.F., 1999. Decreased melatonin levels in postmortem cerebrospinal fluid in relation to aging, Alzheimer’s disease, and apolipoprotein E-ε4/4 genotype. The Journal of clinical endocrinology & metabolism84(1), pp.323-327.

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