Epidemiology of Insomnia: the confusion between symptoms and diagnosis is the rule

The first epidemiological study on insomnia was published less than 35 years ago [1]. From that time, the field has flourished and one can find more than 50 epidemiological studies on insomnia from different parts of the world [2].

In early years of insomnia epidemiology, researchers came up with very high prevalence of insomnia symptomatology (up to 40% of the population in some studies). Narrower definitions in terms of severity and frequency of insomnia decreased the prevalence to 15-20% of the population [2].

Yet, no consensus exists between the classifications on how to define insomnia in terms of symptomatology, frequency and severity:

  • for example, in the DSM-IV, insomnia is defined as a complaint of difficulty initiating or maintaining sleep or of non-restorative sleep that lasts at least one month and causes significant distress or impairment in the individual's functioning.
  • The International Classification of Diseases defines insomnia as difficulty initiating or maintaining sleep occurring at least 3 nights per week for at least one month.
  • Finally, the International Classification of Sleep Disorders defines insomnia as an almost nightly complaint of an insufficient amount of sleep or not feeling rested after the habitual sleep episode.
  • In its mild form, the individual may have little or no evidence of impairment in his or her functioning.

Consequently epidemiologists are using different definitions that lead to different prevalence figures and render very difficult the comparison between the different studies.

This is partly why epidemiological studies are so important and necessary. Nosologically, they provide valuable information on how a clinical description fits a general population and they help to point out the strengths and the gaps in existing classifications. For example, a common belief, confirmed by several studies, is that sleep complaints are increasing with age [2]. However, there is a growing number of epidemiological studies that are showing the relationship aging / insomnia is not linear but the result of a combination of factors [3], [4], [5].

In this specific population, a tight investigation of sleep is primordial before concluding the presence of a sleep disorder. They demonstrate that sleep complaints are mostly the result of co-morbid medical conditions, psychiatric disorders and related health burdens rather than age per se.

The difficulty in studying insomnia in the general population is increased by the fact that insomnia can be a symptom or a diagnosis and the distinction between the two is challenging in the general population. Insomnia can be the symptom of an organic disease, a psychiatric illness or a sleep disorder such as obstructive sleep apnea syndrome or restless legs syndrome but it can be also a diagnosis.

Most epidemiological studies have not attempted to evaluate the diagnostic issues of subjects with insomnia and have limited their analyses to the report of associations. There is a need for valid diagnostic tools of sleep disorders that can be used in the general population.

Epidemiological studies are also useful to determine sleep-wake schedule norms in the general population. Deviations from these norms represent abnormalities that need to be further investigated. Research that analyzes these norms are still scant although this is crucial information.

Epidemiology provides valuable information concerning the natural evolution of sleep disorder. Currently however, few such studies exist [11], [12], [13]. Roberts et al. [14] have done a one-year follow-up study with 4,175 adolescents aged between 11 and 17 years. They demonstrated that insomniac adolescents had an average odds ratio of 2.5 of impaired functioning one year later.

Epidemiology bestows portraits of specific populations at a given time. It provides not only clues about the health needs of insomnia individuals but it also shows where are the lacks in health care systems in terms of recognition of insomnia and adequacy of the medical response.

Prescribed drugs users had more severe insomnia and greater disability than others and participants that used alcohol as sleep-aid had greater daytime sleepiness.

Assessment of adverse events and daytime consequences of insomnia provides important information to improve work conditions in specific populations.
Two articles deal with these questions:

  • Akerstedt et al. [16] using a huge sample of 47,860 employees related sleep disturbances to hectic work, physically strenuous work and shift/night work.
  • In another study, Ohayon et al. [17] investigated the effects of work schedule in the employees of a hospital.

They underlined that rotating daytime shifts had adverse events on sleep. It appeared that it was not the bedtime variation but the fluctuation of the wake up time that had more negative impacts on daytime functioning and sleep.

Repeatedly in the past decade, researchers involved in the field of sleep medicine have reported the lack of medical response despite the fact that individuals with insomnia are huge health care consumers [18].The truth is that sleep medicine is an underprivileged field in medical education with few hours devoted to the teaching of sleep disorders.

The study of Ohayon and Hong [9] performed in the general population of South Korea illustrates this aspect. They found that 5% of their sample has an insomnia disorder diagnoses but of those only 6% of them have sought medical help for their insomnia.
In South Korea, home remedies were the most popular method to treat insomnia. Even in Western countries only 25% to 30% insomnia sufferers consulted about their problem [19], [20]. Often patients do not see sleep problems as an illness and doctors and patients effectively conspire to ignore sleep problems.


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Content of this page is extracted from:
Ohayon MM. Conference, Sleep Epidemiology Center, Palo Alto, 2002.