What are the contributing factors for insomnia in the general population?

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Abstract

Lack of a systematic assessment of insomnia has led to large variations in its reported prevalence in the general population. This study aims to provide new guidelines to assess insomnia prevalence. A cross-sectional telephone survey using the Sleep-EVAL system was done with 24,600 general population-based subjects 15 years and older representative of general populations (France, the UK, Germany, Italy, Portugal, and Spain) consisting of 251,405,391 inhabitants. The overall participation rate was 81.0%. Within the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) symptomatology for insomnia, 27.2% (95% confidence interval: 26.6–27.8%) of the sample reported difficulty initiating sleep (DIS) (10.1%) or maintaining sleep (DMS) (disrupted sleep (DS): 18.0%; early morning awakening (EMA): 10.9%) or nonrestorative sleep (NRS) (8.9%) at least three times per week; 48.5% of them were concomitantly suffering of a DSM-IV sleep/mental disorder. A factor analysis identified several variables strongly related to each of the major factors of insomnia allowing: (1) The narrowing of the definition of insomnia: the prevalence of insomnia decreased to 16.8% with 64.5% of insomnia subjects having a DSM-IV sleep/mental disorder; (2) The identification of a sleep-deprived (voluntary or not) group without insomnia symptoms, representing 2.1% (1.9–2.3%) of the sample. Interestingly, the latter group closely matched the definition of insufficient sleep syndrome as described by the International Classification of Sleep Disorders (ICSD). Using more delineated criteria to assess insomnia increases the recognition of subjects complaining about sleep. Classifications should be amended to improve the correct identification of insomnia. Sleep-deprived subjects should also not be neglected.

Introduction

Although widely studied in the general population [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], insomnia lacks a standard by which to recognize its presence. As a consequence, it is difficult to compare results among countries and to determine the value of insomnia symptomatology to improve its recognition in clinical settings. The definition of insomnia symptoms has greatly varied, as has the number of symptoms assessed, their duration, and their association with sleep/mental disorders. Indeed, some studies used only the reports of difficulty initiating (DIS) or maintaining sleep (DMS) as insomnia symptoms [2], [5], [8], [11]. Others also used a frequency [1], [3], [13], [21], [22], [23], [24], [25] or an intensity scale [6], [7], [9], [12], [14] to determine the presence of insomnia. It is therefore almost impossible to compare the results of these studies. Foremost, an important problem remains: we do not know what the weight of these symptoms is in the diagnosis of sleep or mental disorders. The reported high prevalence of insomnia in these studies suggests that many of the subjects may have been without a true disorder. Furthermore, a part of the population is probably missing because these individuals failed to report insomnia symptoms [19].

From 1993 to 1999, 24,600 subjects from six European countries were extensively questioned about their sleeping habits and sleep/mental disorders. The goal was to tighten the definition of insomnia symptoms in order to increase its recognition in the general population and its associated sleep and mental disorders.

Section snippets

Subjects

This study included 24,600 subjects, representative of the general population aged 15 years and older from France (n=5622), the UK (n=4972), Germany (n=4115), Italy (n=3970), Portugal (n=1856), and Spain (n=4065). These six countries totaled 251,405,391 inhabitants of the European community.

The methodology was the same in each country. The samples were drawn using a two-stage procedure. At the first stage, the sample was chosen according to the geographic distribution of the country as per the

Results

Overall, 24,600 subjects were included in the analyses. Six different strategies were used to analyze the data:

Discussion

This is the first large-scale epidemiological study (N=24,600) that attempts to delineate the importance of insomnia symptoms in relationship to sleep and mental disorders.

Conclusion

This is the first attempt to redefine insomnia recognition through a very large sample of the general population. New decision trees to improve classifications such as DSM-IV or ICSD were described and tested through the large set of variables collected in six European countries. Insomnia is a prevalent pathology in the general population that may cause severe consequences in daily life. Increasing accuracy of insomnia symptomatology identification will help clinicians to recognize pathological

Acknowledgements

This research was supported by the Fond de la Recherche en Santé du Quebec (FRSQ, grant #971067) and by an unrestricted educational grant Sanofi-Synthelabo group. The collaboration of Prof. Robert G. Priest (University of London, England), Prof. Jürgen Zulley (University of Regensburg, Germany), Prof. Salvatore Smirne (State University and Istituto Scientifico San Raffaele, Italy), Prof. Teresa Paiva (Hospital de Sta. Maria, Portugal), and Dr. Teresa Sagales (Hospital General Univ. Vall

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