Several epidemiological studies have been conducted in order to estimate the prevalence of insomnia in the general population. The reported prevalence rates vary considerably, and differences in how insomnia is defined contribute to this variation.
Also, some variability may be explained by differences in how information is obtained, that is, questionnaire or interview surveys.
Some studies report insomnia symptoms, that is, difficulties initiating and/or maintaining sleep, without restrictive criteria, while others include duration, frequency, or severity criteria. Studies without restrictive criteria produce prevalence estimates from 25% to 48% [
Subjects with insomnia generally report shorter sleep duration compared to normal sleepers [
It is important to have accurate estimates of the sex- and age-related prevalence of insomnia and its correlates in the general population in order to understand the public health effect of the disorder. Given the differences in the definition of insomnia in epidemiological research it is difficult to draw conclusions about the true prevalence of the disorder.
This study aims to evaluate the prevalence of insomnia and to identify factors associated with insomnia in the general adult population in Sweden. We used a definition of insomnia disorder that includes insomnia symptoms and detrimental effects on daytime functioning, and our definition of insomnia disorder is thereby close to the DSM-IV insomnia disorder diagnosis [
The study was initiated by the Swedish Council on Health Technology Assessment (SBU). Data were collected by a telephone interview commissioned to the Central Bureau of Statistics (SCB), a governmental agency, in Sweden. Data collection was done with a software package designed specifically for this type of computer-assisted phone survey. After a brief description of the aims of the study and after obtaining verbal consent to proceed with the interview, data were collected.
A sample of 1,550 subjects living in Sweden, 18–84 years of age, representative for the population and proportionally stratified for age and sex was selected for a telephone interview. The interview was completed by 1128 subjects (72.8%). The characteristics of the sample are shown in Table
Characteristics of the sample (
Men | Women | |||
---|---|---|---|---|
|
% |
|
% | |
Age groups (years) | ||||
18–29 | 117 | 21.7 | 106 | 18.0 |
30–39 | 102 | 18.9 | 89 | 15.1 |
40–49 | 87 | 16.1 | 111 | 18.9 |
50–59 | 78 | 14.4 | 90 | 15.3 |
60–69 | 95 | 17.6 | 101 | 17.2 |
70–84 | 61 | 11.3 | 91 | 15.5 |
Physical and psychiatric disorders | ||||
Hypertension | 68 | 12.6 | 107 | 18.2 |
Asthma | 68 | 12.6 | 73 | 12.4 |
Heart disease | 37 | 6.9 | 39 | 6.6 |
Diabetes | 35 | 6.5 | 27 | 4.6 |
Gastrointestinal disorder | 86 | 15.9 | 134 | 22.8 |
Urogenital disorder | 37 | 6.9 | 36 | 6.1 |
Cancer | 17 | 3.1 | 14 | 2.4 |
Joint pain | 98 | 18.1 | 172 | 29.3 |
Fibromyalgia | 2 | 0.4 | 20 | 3.4 |
Other physical disorders | 45 | 8.3 | 90 | 15.3 |
Psychiatric disorder | 26 | 4.8 | 41 | 7.0 |
Burnout | 19 | 3.5 | 35 | 6.0 |
Depression | 42 | 7.8 | 70 | 11.9 |
Sleep duration (hours) | ||||
Weeknights (mean ± SD) |
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|
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Weekends/days off (mean ± SD) |
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|
The interview consisted of 39 questions covering demographics, work conditions, sleep complaints, daytime impairment due to sleep complaints, sleep duration, physical and psychiatric disorders, need for treatment, and usage of prescriptive sleep medication.
Sleep initiation problems were assessed by asking “How often have you had difficulties falling asleep during the last month?” to be answered on a five-point scale (1 = never or less than once a month; 2 = less than once a week; 3 = 1-2 times per week; 4 = 3–5 times per week; 5 = daily or almost daily). Sleep maintenance problems were assessed by asking “How many times do you wake up during the night?” to be answered on a five-point scale (1 = never; 2 = once; 3 = twice; 4 = 3-4 times; 5 = at least 5 times). Insomnia symptoms were defined as sleep initiation problems at least 3 times per week (scores 4 and 5) and/or sleep maintenance problems at least 3 times per night (scores 4 and 5).
Daytime consequences were assessed by asking “Have your sleep complaints interfered with your daily life during the last month?” (1 = no interference, 2 = minor interference; 3 = moderate interference; 4 = severe interference; 5 = very severe interference).
Insomnia disorder was defined as having insomnia symptoms and at least moderate interference with daytime functioning (scores 3 to 5).
Sleep duration was assessed by asking subjects to estimate sleep duration on weeknights and on days off/weekends. The answer was expressed as a continuous variable. Physical and psychiatric disorders were ascertained by asking (in a yes/no question) if respondents had hypertension, asthma, heart disease, diabetes, gastrointestinal disorder, urogenital disorder, cancer, joint pain, fibromyalgia, psychiatric disorder, burnout, depression, or any other disorder.
Subjects were asked (in a yes/no question) “Do you think you need treatment for your sleep problems?” Usage of prescriptive sleep medication was ascertained by the question “How often during the last month have you used prescriptive sleep medication?” (1 = never or less than once per month, 2 = less than once per week, 3 = 1-2 times per week, 4 = 3–5 times per week, and 5 = daily or almost daily). Usage at least 3 times per week (scores 4 and 5) was considered regular usage. Unfortunately we do not have any information about the nature of sleep medication. The type of sleep medication asked about was “on prescription,” that is, not sold over the counter. In Sweden the dominating drugs in this class are zopiclone, zolpidem, and propiomazine.
All analyses were carried out using IBM SPSS Statistics, version 20.0. Standard methods were used to calculate mean values and standard deviations (SDs).
When the comparison involved continuous variables the Mann-Whitney
Ninety-five percent confidence intervals were calculated for prevalence rates and odds ratios. Linear regression models were used to calculate correlations between continuous variables. To identify associations between insomnia disorder and physical and mental disorders age-adjusted and multivariate logistic regression analyses were conducted. Results are presented as odds ratios (OR) with 95% confidence intervals.
The prevalence of having difficulties initiating sleep only was 10.7%, and the prevalence of having sleep maintenance problems only was also 10.7%. The prevalence of insomnia symptoms, that is, sleep initiation problems and/or sleep maintenance problems, was 24.6%. Women reported insomnia symptoms more often than men, 29.3% versus 19.4% (
Prevalence (%) and odds ratios (95% confidence interval) of insomnia symptoms and insomnia disorder by age groups in men (
Insomnia symptoms | Insomnia disorder | |||
---|---|---|---|---|
Men | Women | Men | Women | |
Age groups (yrs) | ||||
18–29 | 16.2 |
23.6 |
6.8 |
9.4 |
30–39 | 17.6 |
32.6 |
6.9 |
13.5 |
40–49 | 18.4 |
26.1 |
11.5 |
21.6 |
50–59 | 15.4 |
27.8 |
5.1 |
13.3 |
60–69 | 21.1 |
30.7 |
4.2 |
12.9 |
70–84 | 31.1 |
36.3 |
8.2 |
9.9 |
|
||||
Total | 19.4 |
29.3 |
7.1 |
13.6 |
Of those with insomnia symptoms 42.9% reported concomitant impairment of daytime functioning and were classified as having insomnia disorder. The prevalence of insomnia disorder was 10.5%, and more women than men reported insomnia disorder, 13.6% versus 7.1% (
Subjects with insomnia disorder reported shorter sleep duration on weeknights compared to subjects without insomnia disorder,
Sleep duration on week nights and on weekends/days off in subjects with insomnia disorder (
Sleep duration on week nights (hrs) | Sleep duration on weekends/days off (hrs) | |||
---|---|---|---|---|
Mean | SD | Mean | SD | |
Subjects with insomnia disorder | 5.77 | 1.64 | 7.04*** | 2.41 |
Subjects without insomnia disorder | 7.03 | 1.05 | 7.86*** | 1.37 |
SD: standard deviation:
Having at least one physical or psychiatric disorder was reported by 82.8% of subjects with insomnia disorder compared to 54.2% of subjects without insomnia disorder (OR, 1.78; 95% CI, 1.58–1.98;
Prevalence (%) and odds ratios (95% confidence interval) of physical and psychiatric disorders in subjects without insomnia disorder (
Subjects without insomnia disorder | Subjects with insomnia disorder | Subjects with insomnia; univariate analysesa | Subjects with insomnia; multivariate analysesb | |
---|---|---|---|---|
% | % | OR (95% CI) | OR (95% CI) | |
Hypertension | 14.8 | 22.4 | 1.67 (1.04–2.67) | 0.98 (0.53–1.83) |
Asthma | 10.9 | 25.6 | 2.81 (1.77–4.44) | 1.96 (1.11–3.44) |
Heart disease | 5.9 | 14.4 | 2.69 (1.51–4.80) | 1.13 (0.50–2.54) |
Diabetes | 5.1 | 8.5 | 1.75 (0.86–3.54) | 1.53 (0.67–3.51) |
Gastrointestinal disorder | 16.3 | 45.8 | 4.32 (2.90–6.44) | 2.36 (1.46–3.82) |
Urogenital disorder | 5.8 | 12.7 | 2.38 (1.30–4.34) | 1.72 (0.80–3.66) |
Cancer | 2.8 | 2.5 | 0.91 (0.27–3.04) | 0.30 (0.07–1.24) |
Joint pain | 21.3 | 46.6 | 3.22 (2.18–4.76) | 1.91 (1.16–3.15) |
Fibromyalgia | 1.1 | 9.5 | 9.41 (3.98–22.23) | 5.04 (1.88–13.53) |
Other physical disorder | 11.2 | 18.6 | 1.83 (1.10–3.02) | 1.16 (0.63–2.13) |
Psychiatric disorder | 3.7 | 24.1 | 8.32 (4.86–14.23) | 2.00 (0.91–4.37) |
Burnout | 2.5 | 23.7 | 12.17 (6.81–21.76) | 2.19 (0.99–4.85) |
Depression | 6.2 | 40.5 | 10.40 (6.64–16.28) | 4.91 (2.63–9.17) |
OR: odds ratio; CI: confidence interval findings are significant when CIs do not include 1.00.
bMultivariate analyses adjusted for age in 5-year strata, all physical and psychiatric disorders.
Among those with insomnia disorder 62.5% expressed a need for treatment, and 22.0% used prescriptive sleep medication regularly. There was no age or sex difference in expressed need for treatment or usage of sleep medication. Subjects with insomnia disorder who were depressed used sleep medication more often than insomniacs without depression, 33.3% versus 17.1% (OR, 3.00; 95% CI, 1.22–7.37;
The main finding of the present study is that the prevalence of insomnia disorder is 10.5%, and women are 2.08 more likely to report insomnia disorder. Insomnia disorder did not increase with advancing age since being older decreased the probability of daytime impairment due to insomnia symptoms. There was, however, a significant rise in reports of insomnia disorder in women aged 40–49 years. Subjects with insomnia disorder slept less than 6 hours on weeknights, but 42.4% were able to extend sleep with more than 1 hour on days off/weekends. There was a strong overlap between insomnia disorder and physical and psychiatric disorders, most often with depression. A majority of subjects with insomnia disorder expressed a need for treatment, indicating that they are troubled and worried about their sleep, while 20.0% used sleep medication.
Advantages of the present study include the nationally representative sample, the high response rate, the broad age range, the comprehensive definition of insomnia disorder, and the wide range physical and psychiatric disorders included. Data were collected by telephone interview, and telephone interviews assessing DSM-IV psychiatric disorders have been shown to yield results comparable to other strategies [
One limitation is that sleep maintenance problems were assessed by the number of awakenings, and an additional question about duration of wake time would have been good. However, we think that 3 or more awakenings will include most individuals with sleep maintenance problems. This categorization has been shown to be related to daytime symptoms [
The measure of physical and psychiatric health according to number of disorders reported is relatively coarse but common in epidemiologic studies. The reliability of some self-reported diagnoses, for example, diabetes, is good [
This study demonstrates that subjects with insomnia disorder had a higher prevalence of several physical and psychiatric disorders compared to subjects without insomnia disorder. The cross-sectional nature of the study does not permit us to disentangle cause and effect; we can only demonstrate associations. Insomnia disorder and other health problems are either causally related to each other or other factors may influence this relationship. As such, we cannot say that insomnia disorder is a result of a physical or psychiatric disorder or that insomnia caused or exacerbated the disorder. However, from longitudinal studies we know that insomnia disorder actually plays a role in disorder development [
One aim of the present study was to provide valid estimates of the prevalence of insomnia disorder. Our definition of insomnia disorder is based on insomnia symptoms with frequency criteria, accompanying daytime consequences and a duration criterion of four weeks, and is thereby close to the DSM-IV insomnia disorder diagnosis [
In this study insomnia disorder was more common in women, but we found no association with advancing age. There was, however, a significant rise in insomnia disorder in women aged 40 to 49 years. Other surveys have also demonstrated a rise in insomnia disorder frequency in middle rather than old age [
It has been shown that women more easily express emotional distress and somatic symptoms, like sleep complaints, compared to men [
Although the elderly have difficulties initiating and maintaining sleep many do not report daytime impairment. With advancing age sleep becomes more fragmented and “lighter” due to increased percentage of stage one sleep and decreased percentage of slow wave sleep [
Generally epidemiological surveys only assess sleep duration without comparing sleep on weeknights to sleep on days off/weekends. In agreement with previous studies subjects with insomnia disorder reported shorter sleep duration than subjects without insomnia disorder [
Our study confirms that insomnia disorder rarely occurs alone. It is by far more common as a comorbid condition than as a single sleep problem. We found that 82.8% of subjects with insomnia disorder reported one or more disorders which is similar to findings from a survey where 86.1% of subjects with insomnia reported medical health problems [
In the present study a majority of subjects with insomnia disorder expressed a need for treatment, while 20.0% used prescribed sleep medication regularly. Other surveys from different countries report that a majority of subjects with insomnia do not use sleep medication. Rates of sleep medication usage in subjects with insomnia range from 21.5% to 33.2% [
This study provides important information about several aspects of the epidemiology of insomnia disorder, and the results have public health implications. The prevalence of insomnia disorder was 10.5%, and it did not increase with advancing age. This may suggest that many elderly adapt their life stylein such a way that potential daytime consequences of disturbed sleep are not manifested. Insomnia disorder was strongly related to physical and psychiatric disorders, most notably depression, underlining the importance of investigating and treating insomnia in subjects with physical and psychiatric disorders. The cause-effect relationship is difficult to establish, but there is evidence that treatment of insomnia disorder should be considered separately and independent of other cooccurring disorders [
The authors declare that there is no conflict of interests regarding the publication of this paper.
Research grants were provided by the Swedish Research Council, Stockholm Council Research Foundation, and SBU (the Swedish Council on Health Technology Assessment).