Aetiology

Insomnia is prevalent in 10-15% of the general population although figures vary significantly globally (1):

• one UK study showed that 69% of older people with insomnia still had it after 1 year, while in younger age groups this figure was 44% (2)

There is a great variation in the amount of sleep that is required by different individuals and it is likely that many people who report sleep difficulty are having enough sleep without realising it. It can be divided into:

• idiopathic insomnia - a persistent disease which begins during infancy or childhood
• psychophysiological insomnia - caused by heightened arousal and learned sleep-preventing associations
• paradoxical insomnia - patient complains of severe insomnia without any objective evidence of sleep disturbance

Causes of comorbid insomnia include:

• psychosocial stressors
  • situational stress - occupational, interpersonal, financial, academic, medical
  • environmental stressors - noise
  • death or illness of a loved one
• psychiatric disorders - particularly anxiety and depression - are the most common comorbidities (3,4)
  • mood disorders: depression, bipolar disorder, dysthymia
  • anxiety disorders: generalized anxiety disorder, panic disorder, post-traumatic stress disorder
  • psychotic disorders: paranoia, schizophrenia, delusional disorder
• medical disorders . Patients with chronic medical conditions have a higher prevalence of insomnia than the general population (5,6,7,8)
  • cardiovascular - angina, congestive heart failure
  • respiratory - chronic obstructive pulmonary disease, asthma
  • neurological - Alzheimer disease, Parkinson disease, head injury
  • rheumatological - fibromyalgia, chronic fatigue syndrome, osteoarthritis
  • gastrointestinal - gastroesophageal reflux disease, irritable bowel syndrome
  • sleep disorders - restless legs syndrome, sleep apnoea, circadian rhythm disorders
  • pain disorders in particular have an especially strong correlation with insomnia.(9)
• drug and substance abuse
  • excessive use of alcohol or alcohol (after stopping heavy drinking sleep may be disturbed for several weeks)
  • tobacco
  • recreational drugs
• medication
  • anti-hypertensives - beta-blockers
  • lipid lowering - statins
  • antidepressants - selective serotonin reuptake inhibitors, venlafaxine, bupropion, duloxetine, monoamine oxidase
  • hormones - oral contraceptive pills, cortisone, thyroid supplement
  • sympathomimetics - salmeterol, theophylline, pseudoephedrine

One meta-analysis of randomised controlled trials found that acetylcholinesterase inhibitors, dopamine agonists, and selective serotonin reuptake inhibitors were the classes of drug most likely to be associated with sleep disturbance (10)

References:

1. Kaur H. et al. Chronic Insomnia. StatPearls Publishing. 2024 Jan.
2. Morphy H, Dunn KM, Lewis M, et al. Epidemiology of insomnia: a longitudinal study in a UK population. Sleep. 2007 Mar;30(3):274-80.
3. Pigeon WR, Bishop TM, Krueger KM. Insomnia as a precipitating factor in new onset mental illness: a systematic review of recent findings. Curr Psychiatry Rep. 2017 Aug;19(8):44.
4. Hertenstein E, Feige B, Gmeiner T, et al. Insomnia as a predictor of mental disorders: a systematic review and meta-analysis. Sleep Med Rev. 2019 Feb;43:96-105.
5. Parthasarathy S, Vasquez MM, Halonen M, et al. Persistent insomnia is associated with mortality risk. Am J Med. 2015 Mar;128(3):268-75.
6. Jarrin DC, Alvaro PK, Bouchard MA, et al. Insomnia and hypertension: a systematic review. Sleep Med Rev. 2018 Oct;41:3-38.
7. He Q, Zhang P, Li G, et al. The association between insomnia symptoms and risk of cardio-cerebral vascular events: a meta-analysis of prospective cohort studies. Eur J Prev Cardiol. 2017 Jul;24(10):1071-82.
8. Vgontzas AN, Liao D, Pejovic S, et al. Insomnia with objective short sleep duration is associated with type 2 diabetes: a population-based study. Diabetes Care. 2009 Nov;32(11):1980-5.
9. Mathias JL, Cant ML, Burke ALJ. Sleep disturbances and sleep disorders in adults living with chronic pain: a meta-analysis. Sleep Med. 2018 Dec;52:198-210.
10. Doufas AG, Panagiotou OA, Panousis P, et al. Insomnia from drug treatments: evidence from meta-analyses of randomized trials and concordance with prescribing information. Mayo Clin Proc. 2017 Jan;92(1):72-87.