Leger, Damien, 5/1/2007
Epidemiology of Insomnia
Damien Leger, MD, Ph D,
Head of Sleep and Vigilance Center, Rare Hypersomnia Reference Center.
Hotel Dieu de Paris, Assistance Publique Hopitaux de Paris and University of Paris 5 , School of Medicine, Paris, France.
Damien Leger, MD, Ph. D.
Centre du Sommeil et de la Vigilance
Hotel Dieu de Paris
1 pl. du Parvis Notre Dame
75181 PARIS CEDEX 04
Phone: 33 1 42 34 82 43
Fax: 33 1 42 34 82 27
Insomnia is a very common complaint among the general population of adults around the world [1,2]. Despite this high prevalence, insomnia is however still unrecognized by health professionals. One issue stands in the fact that insomnia is frequently considered as a symptom rather than as a true disease and is not clear for practitioners if it could be a symptom and a disease. Another difficulty is that it is often difficult for patients and for health professionals to understand when insomnia is severe enough to need a treatment. Then there is still insufficient knowledge about the management of insomnia. In the last decade several consensus meetings about insomnia, its recognition, diagnosis and treatment have been made [3-8], all these consensus groups have underlined the impact of insomnia on public health and the need to better encompass the consequences of insomnia on work, economics and quality of life. There is however very few international data comparing insomnia in the population of different countries around the planet.
The aim of this contribution is describe carefully the epidemiological issues of insomnia and its public health consequences and to point out what are the certitudes and the missing data we need for a better comprehension of the impact of insomnia in the daily lives of patients.
Epidemiology: magnitude of insomnia.
- Epidemiology and definition.
Insomnia has to be clearly defined if we want to accurately know its prevalence in the general population. The first surveys have inquired about sleep disorders in the life time and they have found as much as 90% of subjects complaining of poor sleep . These data are confusing and more recently the DSM-IV or ICSD definitions of insomnia have been more largely applied in epidemiological settings. Several large samples have been studied in the last decade. In 2002, Ohayon and Smirne  conducted a study with a representative sample of the United Kingdom population of 3970 individuals aged 15 years or older: insomnia symptoms were reported by 27.6% of the sample. Sleep dissatisfaction was found in 10.1% and insomnia disorder diagnoses in 7% of the sample. The use of sleep-enhancing medication was reported by 5.7%. Leger et al. epidemiological questionnaire survey of a representative sample of the French population that included 12 778 individuals found a prevalence of insomnia of 19% with 9% presenting severe insomnia (at least two symptoms of insomnia according to the DSM-IV definition) . Kim et al. found a prevalence of 21.4 % of insomniacs in a 3000 sample representative of the general population of Japan . In the United States, the most recent study has been made by the National Sleep Foundation on a representative sample of 1506 subjects over 18 years old in 2004. 21% of the sample complained of insomnia according to the ICSD definition, but only 9% had insomnia and daytime consequences . A compilation of the recent studies have been made by Ohayon in 2002 and assessed that insomnia usually concern around one adult on three in the general population . However from 16 to 21% only have insomnia at least three times a week, from 13 to 17% qualify their trouble as important or major and 9 to 13% have insomnia and daytime consequences. To our knowledge, there is still no epidemiological study using the new research criteria .
- Socio demographics
Almost all studies show an increasing prevalence of insomnia with age and a sex ratio in favor of women [1-7]. In a 12 778 sample, Leger et al found that severe insomnia was almost twice as high for women as for men (12% vs. 6.3%; p < 0.0001) . Older subjects have usually more severe complaints than younger. In a representative sample (n = 5 622) of the general population of France aged 15 or older, Ohayon and Lemoine found that the prevalence of insomnia was twice more frequent in subjects 65 years of age or older compared to subjects younger than 45 years . Moreover, in this last study, 47.1% of subjects above 65 years reported three symptoms of insomnia compared to 32.2% of subjects under 44 tears old (p <0.001). However younger subjects (under 45 years) and females had significantly more daytime consequences of insomnia than older and males.
There are few studies trying to support the link between perceived job stress and the prevalence of insomnia except the study made by Nakata et al in 1161 male white-collar employee of a Japanese electric equipment company surveyed by a mailed questionnaire . This study found an overall prevalence rate of insomnia of 23.6% Workers with high intragroup conflict (OR 1.6), high job dissatisfaction (OR 1.5) had a significantly increased risk of insomnia after adjusting for multiple confounding factors. Low employment opportunities, physical environment and low coworker support also were weakly associated with a risk of insomnia among workers.
Insomnia is also generally higher in persons with low socio-economical status . In the French population, the prevalence of insomnia was the highest in the white collar group (20, 8%) . It was also found a trend towards lower rates of insomnia in upper level executives, liberal professions and in farmers group. Doi et al, in a cross sectional study including 4868 day time white-collar workers similarly showed that poor sleep was significantly more prevalent in white collars (30 to 45 %) than in the Japanese general working population . Recently, Gellis et al, have investigated the likelihood of insomnia and insomnia-related health consequences among a sample of at least 50 men and 50 women in each age decade from 20 to 80+ years old and of different socioeconomic status . Results indicated that individuals of lower individual and household education were significantly more likely to experience insomnia, even after researchers accounted for ethnicity, gender, and age. Additionally, individuals with fewer years of education, particularly those who had dropped out of high school, experienced greater subjective impairment because of their insomnia.
- Seeking help and access to the treatments
Insomniacs and even severe insomniacs are not always seeking help for treatment. Years ago, the Gallup study found that only 5% of insomniacs had ever visited a physician to dis¬cuss specifically their sleeping problem and that only 21% had ever taken a prescription medication for sleep . In France 53% of severe insomniacs vs. 27% of subjects with occasional sleep problems reported they had ever visited a doctor specifically for insomnia (p<10 4) . A lot of persons with sleep dissatisfaction are just watching television, reading, using non prescription medication, or drinking alcohol to promote sleep . In a survey in the Detroit area of a rep¬resentative sample of 2,181 adults aged 18 45, Johnson et al. found that 13.3% used alcohol as a sleep aid in the past year and 10.1% an over the counter prescription . Fifteen percent of those who used alcohol as a sleep aid did it for at least one month; however the duration of use was short for the majority of users (less than one week). Only 5.3% used a prescription medication. However, 10.8% of French adults regularly used prescription medication to promote sleep . Recently a consecutive sample (n = 700) of adults attending a non-urgent primary care appointment was screened for sleep problems in the U.S. A follow-up mailed survey then assessed insomnia symptoms, daytime impairment, beliefs about sleep, medication use, sleepiness and fatigue, and medical help-seeking . They conversely found that a high 52 % of patients with probable insomnia reported discussing this with a physician. Multivariate logistic regression analyses indicated that discussing one's probable insomnia with a physician was independently associated with having a greater number of medical conditions (OR, 2.19 [95% CI, 1.13 to 4.22]), being more highly educated (1.67 [95% CI, 1.11 to 2.51]), sleeping less per night (OR, 0.71 [95% CI, 0.52 to 0.96]), and greater perceived daytime impairment due to insomnia (OR, 2.07 [95% CI, 1.06 to 4.03]).
Diagnosis of insomnia is not always followed by treatment. In Germany, a Nationwide Insomnia Screening and Awareness Study (NISAS-2000) found that close to 50% of all patients with insomnia did not receive a prescription for a specific insomnia therapy .
- Natural history
There are very few data on the natural history of insomnia. Severe insomnia seems to be more persistent than mild insomnia. Katz and Mc Horney have reassessed two years later a group of 3445 patients with insomnia: 83% of patients with severe insomnia remained so categorized, compared to 59% of patients with mild insomnia . Hohagen et al. have also shown that 4 months after a first survey, 87% of patients who initially reported a sleep complaint still have a sleep complaint . According to Mendelson et al., 88.2% of patients continue to report sleep problems five years after the onset . Predisposing, precipitating and perpetuating factors contribute in the natural history of insomnia of subjects presenting variable vulnerability [26, 27]. In a recent study of 345 patients evaluated for insomnia at a sleep-disorders clinic in Quebec, Bastien et al have identified, the specific precipitating events related to the onset of insomnia. The most common precipitating factors of insomnia were related to family, health, and work-school events. Sixty-five percent of precipitating events had a negative valence. These events differed with the age of onset of insomnia but not with the gender of participants  .
- Comorbidty with depression and anxiety
Insomnia is associated with a variety of medical and psychiatric conditions. It is usually more easy to clarify how insomnia is due to medical problems than to understand how insomnia is a cause or a consequence of psychiatric diseases. Comorbidities with depression and anxiety are estimated to occur in 35 to 60% of chronic insomniacs [1, 4-7,27,29-30]. Several longitudinal studies have shown that insomnia may represent a substantial and statistical risk for the development of depressive disorders [31-33]. However, there is actually an increasing support to believe that the coexistence of these two disease reflect a common pathology rather than two separate diseases. In order to clarify public health consequences due to insomnia by itself, it seems however important to clearly identify insomniacs with psychiatric diseases in the design of the studies.
Even though there is broad consensus on the fact that daytime impact is a major criterion in the definition of insomnia [7-9], the precise nature of this impact remains subject to debate. In a review of insomnia and daytime functioning, Riedel and Lichstein suggested that the lack of objective findings in the literature might be explained by (a) a focus on variables that are not impaired (rather than areas of actual impairment) and (b) methodological problems (such as non-homogeneous groups of subjects) which may have hidden actual differences between insomniacs and good sleepers . Daytime sleepiness has received the most attention but it is becoming clear that a large number of insomniacs are not sleepy during the day [35-36]. Bonnet and col. have even used MSLTs to demonstrate that insomniacs were more alert in the daytime than good sleepers . However, the absence of an objective somnolence deficit does not mean that insomniacs are not impaired during the daytime.
Riedel and Lichstein also recommended using objective measures of work performance (absenteeism, promotion, etc.) to clarify the impact of insomnia on daytime functioning . Insomnia is not a visible handicap in the workplace and it is difficult for insomniacs to explain to their colleagues and managers that they have had a poor night and that they need to rest… Insomniacs have to face a regular work load and they often complain of difficulties in their professional life [25, 37-38]. However, there are few data assessing the true impact of insomnia on daily work. This is a crucial point to try to evaluate the impact of insomnia on absenteeism and other work measures in a real setting.
Millions of people are suffering of insomnia around the world. In addition to its nocturnal effect insomnia affects deeply the daily lives of patients. The economic impact of insomnia on the collectivity seems enormous. There is also an increasing evidence linking insomnia to several severe public health concerns: obesity, diabetis, depression, cardio-vascular diseases.
There is a major need for education of doctors and information of the general public about sleep, insomnia and the management of this disorder;
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