Sleep Medicine 15 (2014) 173–179
Contents lists available at ScienceDirect
Sleep Medicine journal homepage: www.elsevier.com/locate/sleep
Original Article
A 10-year trend of insomnia prevalence in the adult Norwegian population Ståle Pallesen a,b,⇑, Børge Sivertsen c,d,e, Inger Hilde Nordhus b,f, Bjørn Bjorvatn b,g a
Department of Psychosocial Science, University of Bergen, P.O. Box 7807, N-5020 Bergen, Norway Norwegian Competence Center for Sleep Disorders, Jonas Lies vei 65, 5021 Bergen, Norway c Department of Public Mental Health, Norwegian Institute of Public Health, Kalfarveien 31, 5018 Bergen, Norway d Uni Health, Uni Research Bergen, P.O. Box 7810, N-5020 Bergen, Norway e Department of Psychiatry, Helse Fonna HF, P.O. Box 2170, N-5504 Haugesund, Norway f Department of Clinical Psychology, University of Bergen, P.O. Box 7807, N-5020 Bergen, Norway g Department of Public Health and Primary Health Care, University of Bergen, P.O. Box 7804, N-5020 Bergen, Norway b
a r t i c l e
i n f o
Article history: Received 16 March 2013 Received in revised form 11 October 2013 Accepted 15 October 2013 Available online 1 December 2013 Keywords: Sleep Insomnia Secular Trend Prevalence Epidemiology
a b s t r a c t Objective: We aimed to investigate the 10-year trend in the prevalence of insomnia symptoms, insomnia cases, and use of hypnotic agents in the adult Norwegian population. Methods: Data from two representative surveys assessing identical insomnia symptoms in the adult population of Norway, one conducted in 1999–2000 (N = 2001) and one conducted in 2009–2010 (N = 2000), were compared. Results: Controlling for basic demographic variables, significant increases were found over the 10-year study period in the prevalence of sleep-onset insomnia from 13.1% to 15.2%, dissatisfaction with sleep from 8.2% to 13.6%, daytime impairment from 14.8% to 18.8%, Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) insomnia cases from 11.9% to 15.5%, and hypnotic agent use from 6.9% to 11.1%. No secular trend was found for maintenance insomnia or for early morning awakening insomnia. Across the two surveys, women reported a higher prevalence of insomnia than men. Age was positively associated with the prevalence of nocturnal sleep problems and use of hypnotic agents but was inversely associated with daytime impairment. Individuals with low socioeconomic status (SES) reported a higher prevalence of several insomnia symptoms. Conclusions: Insomnia seems to be on the rise in the general adult population, which gives reason for concern. Prevention of insomnia and cost-effective interventions should receive higher priority in the future. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction Insomnia is characterized by problems initiating or maintaining sleep or nonrestorative sleep, which leads to one or more forms of daytime impairment [1]. Epidemiologic studies have reported a wide range of insomnia prevalence, from approximately 2% [2] to 48% [3], reflecting different ways of defining and assessing insomnia and differences in study samples [4]. This range in prevalence makes comparisons of findings across studies problematic. When insomnia is defined according to formal diagnostic systems, the range of prevalence becomes more narrow and varies between approximately 6% [5] and 12% [6].
⇑ Corresponding author. Address: Department of Psychosocial Science, Faculty of Psychology, Christiesgt. 12, 5015 Bergen, Norway. Tel.: +47 55588842; fax: +47 55589879. E-mail address: [email protected] (S. Pallesen). 1389-9457/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sleep.2013.10.009
Although there are discrepancies between studies of prevalence rates, there seems to be greater consensus about the demographic factors associated with insomnia across studies. Most studies report female preponderance [7], an increasing prevalence with age [8,9], an association between insomnia and low socioeconomic status (SES) [10–12], and an elevated insomnia prevalence in individuals reporting psychiatric [13] and somatic [14] symptoms compared to healthy control participants. Previous perspectives typically have implied that insomnia represented a consequence or a symptom of other disorders [15]. However, newer perspectives based on prospective or longitudinal studies indicate that insomnia can lead to or exacerbate several problematic situations or disorders, such as depression [16], suicidal ideations [17], sick leave [18], disability pension [19], metabolic syndrome [20], pain [21], work accidents [22], and impaired cognition [23]. During the last decades many societal changes that may influence sleep have occurred, such as an expansion of television
174
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179
broadcasts [24]; an increase in nonstandard working hours [25]; an increase in use of electronic devices, including computers, smart phones, video games, among others [26]; the establishment of a 24-h society [27]; and an increase of the proportion of the population who are overweight or obese [28]. However, a systematic review of secular trends in adult sleep duration in 15 countries from the 1960s until the 2000s showed an increase in sleep duration in seven countries but a decrease in six countries, leading the authors to conclude that there has not been any consistent decrease in self-reported sleep duration of adults from the 1960s to the 2000s [29]. Nevertheless, some secular trend studies of insomnia symptoms suggest a worsening of sleep over time. In a study of women in Sweden, cohort comparisons of participants ages 38 or 50 years between 1968–1969 and 2004–2005 suggested that sleep problems had almost doubled in both age groups, whereas the use of sleep medication remained unchanged since 1968 [30]. Data from seven independent cross-sectional representative population surveys performed between 1972 and 2005 in Finland revealed an increase in both occasional and chronic insomnia symptoms across the 33-year period [31]. Comparisons of results from three representative cross-sectional studies of inhabitants of São Paulo, Brazil, conducted in 1987, 1995, and 2007, respectively, showed an approximate 2-fold increase in the proportions reporting difficulty initiating sleep, difficulty maintaining sleep, and early morning awakening over the 20-year time span [32]. However, more studies on the issue of secular trends in insomnia are needed, especially as the number of previous studies is few. In addition, some of the studies only focused on women [30] and some only used global sleep questions that do not discriminate between different insomnia symptoms [30,31]; to our knowledge no previous trend study has reported on daytime impairment. The main goal of our study was to investigate if a change in the prevalence of insomnia symptoms occurred over a 10-year period in the adult Norwegian population. To achieve our goal, we compared survey data collected 10 years apart in representative samples of the adult Norwegian population.
2. Methods 2.1. Participants In 1999–2000 a total of 2001 randomly selected adults aged 18 years and older (1091 women and 910 men) participated in a telephone survey in which they answered questions related to demography and sleep among other variables. Exactly ten years later in 2009–2010, a similar telephone survey was conducted, which included a total of 2000 randomly selected adults (1039 women and 961 men) who answered identical questions. There were no significant differences between the surveys in the gender distribution (v2 = 2.6; df = 1; P > .05). The mean unweighted age of the sample in 1999–2000 was 44.7 years (standard deviation, 15.6), and 48.0 (standard deviation, 17.4) in 2009–2010 (t = 6.4; df = 3951; P < .01). The census data of Norway show that the mean age of adults aged 18 years or older was 46.6 years in 2000 and 47.5 years in 2010, respectively. In 1999–2000, 9.6% of the sample had no education subsequent to mandatory schooling, while 30.3% had one to 3 years, 32.2% had 4–6 years, and 27.8% had more than 6 years of education subsequent to mandatory schooling, respectively. The corresponding figures in the 2009–2010 sample were 8.4%, 33.9%, 31.0%, and 26.8%, respectively (v2 = 6.5, df = 3, P > .05). The numbers of individuals in the age categories (18– 29 years, 30–44 years, 45–59 years, and P60 years) were 456, 572, 456, and 517, respectively, in the 1999–2000 sample. The corresponding figures for the 2009–2010 sample were 378, 576, 518 and 528, respectively.
2.2. Materials In addition to demographic and other background information (e.g., age, gender, education, place of residence, family income), the participants were asked to answer the following questions about their sleep: (1) After you turn off the lights, how long does it normally take you to fall asleep? (2) Do you wake up from sleep before the final morning awakening? If so, what is the total time during the night you are awake? (3) Do you wake up at least half an hour earlier than you wish to? If so, how often has this happened during the previous month (Never, 1–4 days, 5–10 days, 11–20 days, >20 days)? (4) How satisfied are you with your present sleep (very satisfied, somewhat satisfied, neither satisfied nor unsatisfied, somewhat unsatisfied, very unsatisfied)? (5) Is your sleep so poor that it affects your daily activities or duties? If so, how often has this happened during the previous month (Never, 1–4 days, 5–10 days, 11–20 days, more than 20 days)? (6) Do you use sleeping pills prescribed by a medical doctor? If so, how often has this happened during the previous month (Never, 1–4 days, 5–10 days, 11–20 days, more than 20 days)? All questions pertained to the previous month. We also asked two questions about insomnia comorbidity: (1) During the last month, have you had any physical ailment or illnesses (no/yes)? (2) During the last month, have experienced any emotional or psychologic problems (no/yes)? 2.3. Procedure The 1999–2000 survey was part of a telephone omnibus conducted by an opinion-research institute (Norsk Respons). Random telephone numbers were drawn from the customer list of the largest telephone company in Norway covering approximately 98% of all Norwegian households. To ensure a random sample, the next birthday technique was employed, which involved asking to speak with the adult household member who has the next birthday [33]. Half of the interviews were conducted during the first 2 weeks of December 1999 and the other half during the first 2 weeks of June 2000. The response rate was based on the number of those who answered the telephone, which was 56.9%. The results from that survey have been previously published [6]. The 2009–2010 survey also was conducted by an opinion-research institute (Respons Analyse; former Norsk Respons). Half of the interviews were conducted during the first 2 weeks of December 2009 and the other half during the first 2 weeks of June 2010. For the two waves in the 2009–2010 survey, 3000 inhabitants of Norway aged 18 years and older, who were randomly drawn from Norwegian Population Registry, were sent a letter informing them that they might receive a phone call to be invited to participate in a telephone survey about sleep. The response rate was based on the number of those who answered the telephone for the 2009–2010 survey, which was 64.9%. Because no link was made between the responses and the name list or between the responses and the phone numbers, the data were anonymously collected according to Norwegian legislation. For both the 1999–2000 survey and the 2009–2010 survey, no more calls were made when the aim of recruiting 1000 respondents each season was met. In addition, the samples were stratified by the number of inhabitants of all counties for both surveys, thus the census of Norway in county population comprised a sampling criterion. When the proportional number of respondents for each county was met, further recruitment of respondents from that county was terminated. For both surveys, the only inclusion criterion was age (P18 years); no exclusion criteria were employed. Compared to the census of Norway individuals in the youngest (18–29 years) and oldest (P60 years) age groups and men were underrepresented in both the 1999–2000 survey and in the 2009–2010 survey. In the analyses, we adjusted for this variable
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179
by weighing the subgroups according to age and gender of the census of Norway. A weight of less than two was used for all cases. The fees to the opinion research institutes were covered by a grant from the Norwegian Competence Center for Sleep Disorders, funding from the University of Bergen, and a grant from the Norwegian Research Council. Length of education and family income were used as proxies for SES by transforming the scores for those two items into z scores and adding them to create a single composite variable. This process was separately performed for the 1999–2000 and the 2009–2010 survey. Negative z scores indicated an SES below mean, whereas positive z scores indicated a status above mean. For region the five most northern counties of Norway were defined as Northern (62°–71° north) and the other counties were defined as Southern (58°–62° north). Insomnia inclusion criterion 1 of the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) [1], was met if one of the following three subcriteria were met: (1) mean sleep-onset latency exceeding 30 min, (2) mean wake time after sleep onset exceeding 30 min, or (3) waking up at least 30 min earlier than the individual preferred more than 10 days per month. Insomnia inclusion criterion 2 was considered fulfilled if one of the following two subcriteria were met: (a) reporting being somewhat or very unsatisfied with present sleep; or (b) reporting sleep so poor that it affected daily activities or duties more than 4 days per month. The DSM-IV inclusion criteria for insomnia were met if criterion 1 and criterion 2 were both fulfilled and suggested DSM-IV insomnia cases. Because all data were anonymously collected, both surveys were exempted from review by the Ethics Board (The Regional Committee for Medical Research Ethics in Western Norway). 2.4. Statistical analyses Data analyses were conducted by the IBMÓ SPSS Statistics, version 19. All prevalence figures and confidence intervals (CIs) were calculated by weighting the cases according to the population distribution of gender and age to correct for potential divergence between the sample and the distribution of age and gender in the general population of Norway. Weighted prevalence and 95% CIs for all the single insomnia symptoms and for DSM-IV insomnia cases and for use of hypnotics were separately calculated for the 1999–2000 and the 2009–2010 survey. Results also were broken down by gender and age groups (18–29 years, 30–44 years, 45–59 years, and P60 years). A weighted logistic regression analysis was used to investigate if sociodemographic variables (e.g., year, gender, age, SES, region) were related to insomnia and use of hypnotic agents. In step 1, year, gender, age, SES, and region were entered as independent variables, whereas the interaction term year gender was entered in step 2 to investigate if potential secular changes in insomnia differed between the genders. In the logistic regression analyses, age and SES were entered as continuous variables, whereas year, gender, and region were entered as dichotomized variables. Logistic regression analyses, in which only single dependent variable was included (crude), also were conducted. Results from the logistic regression analyses were considered significant when the confidence interval did not include 1.00. To investigate any secular change in somatic and psychiatric comorbidity, we performed v2 tests to determine if the proportion of the samples reporting such symptoms differed between the 1999–2000 and 2009–2010 samples. 3. Results Table 1 shows the prevalence of the different insomnia symptoms including the 95% CIs, broken down by gender and age
175
groups. Table 2 presents the results from the logistic regression analyses. From 1999–2000 to the time of the second survey in 2009–2010, the prevalence changed as follows (reported odds ratios [ORs] are from the adjusted regression analyses): sleep-onset insomnia changed from 13.1% to 15.2% (OR, 1.24 [95% CI, 1.04– 1.49]); maintenance insomnia changed from 16.3% to 17.6% (OR, 1.08 [95% CI, 0.91–1.29]); early morning awakening insomnia changed from 14.0% to 15.0% (OR, 1.06 [95% CI, 0.88–1.27]); dissatisfaction with sleep changed from 8.2% to 13.6% (OR, 1.78 [95% CI, 1.45–2.19]); daytime impairment changed from 14.8% to 18.8% (OR, 1.41 [95% CI, 1.18–1.67]); DSM-IV insomnia cases changed from 11.9% to 15.5% (OR, 1.37 [95% CI, 1.14–1.65]); and hypnotic use changed from 6.9% to 11.1% (OR, 1.72 [95% CI, 1.36–2.17]). Across the two surveys, women reported a higher prevalence of insomnia than men. Age was positively associated with the prevalence of nocturnal sleep problems and use of hypnotic agents, but it was inversely associated with daytime impairment. Individuals with low SES reported a higher prevalence of several insomnia symptoms. We found no secular changes for physical ailment or illnesses (v2 = 0.33; df = 1; P > .05) or for emotional or psychologic concerns (v2 = 3.68; df = 1; P > .05).
4. Discussion The main question that we addressed in our study concerned a possible secular change in the insomnia prevalence in Norway. Our data showed that the prevalence of sleep-onset insomnia, dissatisfaction with sleep, daytime impairment, DSM-IV insomnia cases, and use of prescribed hypnotic agents had all increased during the 10-year period between 1999–2000 and 2009–2010, whereas no significant secular trend was found for the prevalence of maintenance insomnia and early morning awakening insomnia. Thus overall the findings of our study corresponded well with previous trend studies of insomnia prevalence [30–32,34]. Our findings might suggest a possible secular trend in the willingness to report health problems [35], though it is doubtful that this factor explains large proportions of the changes in insomnia prevalence. A more plausible explanation relates to working life, in which studies suggest an increase in occupational stress [36] and in shift work [25] over the years. Another possible explanation involves worsening of sleep habits over time. Recently we reported data showing that the discrepancy between sleep times during weekdays and weekends has increased over the last decades in Norway [37], which is a factor that might contribute to sleep problems. Another potential contributing factor to the secular trend in insomnia reported here comprises the sharp increase in the availability and use of electronic devices, such as mobile phones, video game consoles, computers and tablets [26], as their potential for disturbing sleep has been widely recognized [38,39]. Previously we reported that the use of such devices in the bedroom was associated with delayed bedtimes [40] and other studies have shown that the use of such devices is related to daytime tiredness [41] and prolonged sleeponset latency [42]. The secular increase in body mass index of the general population also may explain the rise in insomnia prevalence, as obesity and overweight can cause sleep-disordered breathing [43] and impaired sleep quality [44]. Because we did not collect data specifically concerning the aforementioned factors, we were precluded from investigating if these factors actually were related to the secular changes in insomnia that we reported in our present study. Thus future studies should more explicitly address these issues. The secular increase found for several insomnia symptoms did not seem to be related to somatic and psychiatric comorbidity, as no secular change concerning these variables was found in our
176
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179
Table 1 Prevalence (%) and 95% confidence intervals for the different insomnia symptoms broken down by age and gender for the 1999/2000 survey and the 2009/2010 survey. Men
Women
1999/2000
2009/2010
1999/2000
2009/2010
Sleep-onset insomnia 18–29 y 30–44 y 45–59 y P60 y
% (95% CI) 16.1 (10.0–22.2) 7.1 (4.3–10.0) 5.0 (2.2–7.8) 13.7 (8.1–19.3)
% (95% CI) 22.5 (16.0–29.0) 10.3 (6.4–14.1) 6.7 (3.4–10.0) 16.2 (11.6–20.8)
% (95% CI) 18.0 (12.4–23.7) 9.5 (6.5–12.5) 13.2 (9.2–17.2) 21.7 (15.1–28.2)
% (95% CI) 20.5 (14.2–26.8) 12.7 (8.8–16.6) 13.6 (9.4–17.8) 22.8 (17.1–28.4)
Maintenance insomnia 18–29 y 30–44 y 45–59 y P60 y
10.5 (5.4–15.6) 7.5 (4.5–10.4) 7.5 (4.2–19.9) 22.6 (15.7–29.5)
5.6 (2.0–9.3) 11.1 (7.1–15.1) 12.5 (8.1–16.9) 19.0 (14.1–24.0)
12.0 12.2 17.1 30.0
12.4 19.4 21.7 27.9
Early morning awakening insomnia 18–29 y 30–44 y 45–59 y P60 y
2.1 ( 0.3 to 4.5) 7.8 (4.8–10.8) 14.6 (10.1–19.2) 24.0 (17.0–31.0)
3.1 (0.4–5.9) 10.3 (6.4–14.1) 16.1 (11.2–20.9) 19.0 (14.1–24.0)
4.4 (1.4–7.4) 7.9 (5.1–10.7) 15.3 (11.1–19.5) 31.2 (23.9–38.5)
7.5 (3.4–11.6) 14.4 (10.3–18.6) 20.9 (15.9–25.9) 22.8 (17.1–28.4)
Dissatisfaction with sleep 18–29 y 30–44 y 45–59 y P60 y
10.5 (5.4–15.6) 6.5 (3.7–9.3) 5.4 (2.5–8.3) 5.5 (1.7–9.2)
11.3 (6.3–16.2) 11.9 (7.8–16.0) 9.8 (5.9–13.8) 11.3 (7.4–15.3)
7.7 (3.8–11.5) 8.2 (5.3–11.0) 5.0 (2.4–7.5) 10.0 (4.9–14.2)
8.7 (4.3–13.1) 15.1 (11.0–19.3) 17.8 (13.1–22.5) 14.0 (9.3–18.6)
Daytime impairment 18–29 y 30–44 y 45–59 y P60 y
17.5 (11.2–23.8) 12.3 (8.6–16.0) 11.3 (7.3–15.3) 3.4 (0.4–6.4)
22.5 (16.0–29.0) 17.3 (12.5–22.1) 13.0 (8.5–17.4) 8.1 (4.7–11.5)
23.0 17.1 13.9 14.0
(16.8–29.1) (13.3–21.0) (9.8–18.0) (8.5–19.5)
27.3 26.1 21.7 16.3
(20.4–34.3) (20.9–31.2) (16.4–26.8) (11.3–21.3)
DSM-IV insomnia cases 18–29 y 30–44 y 45–59 y P60 y
12.6 (7.1–18.1) 5.8 (3.2–8.5) 8.4 (4.8–11.9) 6.9 (2.7–11.0)
11.9 11.9 10.7 12.2
10.4 11.1 10.3 19.8
(5.9–14.8) (7.9–14.4) (6.7–13.9) (13.5–26.0)
12.4 16.6 20.2 16.7
(7.3–17.6) (12.2–20.9) (15.2–25.1) (11.7–21.8)
Use of prescribed hypnotics 18–29 y 30–44 y 45–59 y P60 y
0.0 (0.0–0.0) 1.6 (0.2–3.0) 4.2 (1.6–6.7) 11.6 (6.4–16.9)
3.8 (0.8–6.7) 2.9 (0.8–5.0) 3.6 (1.1–6.0) 17.8 (13.0–22.6)
(6.8–16.9) (7.8–16.0) (6.7–14.8) (8.0–16.3)
(7.3–16.8) (8.9–15.6) (12.7–21.5) (22.7–37.2)
2.2 (0.1–4.3) 3.5 (1.6–5.4) 8.9 (5.6–12.3) 19.1 (12.9–25.3)
(7.3–17.8) (14.7–24.0) (16.6–26.8) (21.9–34.0)
3.1 (0.4–5.8) 6.3 (3.5–9.2) 17.1 (12.4–21.7) 27.9 (21.9–34.0)
Abbreviations: CI, confidence interval; y, years; DSM-IV, Diagnostic and Statistical Manual of Mental Disorders, Fourth Revision.
study. This finding is further corroborated with other studies that reported no increase in psychiatric problems in the Norwegian population during the last decades [45]. The fact that we also found an increase in the use of hypnotic agents does support the overall notion of a secular increase of insomnia in the general population. Although most insomnia symptoms did increase with time, symptoms of maintenance insomnia and early morning awakening insomnia did not for unknown reasons. Compared to men, women had a higher prevalence of all insomnia symptoms, DSM-IV insomnia cases, and use of prescribed hypnotic agents. These results are consistent with previous studies [7]. Age was positively related to insomnia, especially insomnia occurring after sleep onset. This finding most likely reflects a shortening of the sleep-wake rhythm with age [46] and more arousals during sleep with increasing age [47], as well an increase in somatic conditions such as pain [48] and sleep disorders such as obstructive sleep apnea [49]. Age was inversely associated with daytime impairment, which might reflect that younger individuals have a greater sleep debt than older individuals and that elderly individuals have fewer scheduled responsibilities [6]. Our finding that age was positively associated with hypnotic agent use correlates well with previous studies [50]. SES was negatively associated with sleep-onset insomnia, early morning awakening insomnia, daytime impairment, and DSM-IV insomnia cases in our study. These findings are consistent with previous studies [9,10] and suggest that disadvantageous social factors interfere with sleep [6]. Although we previously found that geographic region was related to the
use of hypnotic agents (6), geographic region was not related to any of the dependent variables in our study based on the adjusted analyses, indicating that insomnia symptoms showed an evenly geographic distribution in Norway. Results from the crude regression analyses suggested that the secular development of insomnia did vary by gender; however, these results did not remain significant in the adjusted analyses. 4.1. Methodologic considerations Some limitations of our study should be noted. In the 1999– 2000 survey, the sleep questions were part of a general telephone omnibus, whereas the respondents participating in the 2009–2010 survey received a letter informing them that they might receive a phone call asking them to participate in a telephone survey about sleep. Thus the risk for self-selection (e.g., in respondents with sleep problems) may be greater for the last survey compared to the first survey [51]. The response rate was 56.9% in the 1999– 2000 survey, whereas it was 64.9% in the 2009–2010 survey. Because nonresponse is found to be associated with pathology [52], the proportion of respondents with different forms of pathology might have been higher in the latter survey than in the former, which might have led to inflated insomnia estimates. It also should be noted that the insomnia symptoms assessed in our study do not exclusively pertain to insomnia sleep disorder but also might reflect a wider range of sleep disorders and other disorders known to affect sleep [1]. The 2009–2010 sample was significantly older
177
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179
Table 2 Results from the regression analyses (odds ratio) and 95% confidence intervals in which year, gender, age, socioeconomic status, region, and the interaction term year gender are regressed on different insomnia symptoms (e.g., sleep-onset insomnia, maintenance insomnia, early morning awakening insomnia, dissatisfaction with sleep, daytime impairment); Diagnostic and Statistical Manual of Mental Disorders, Fourth Revision, insomnia cases; and use of prescribed hypnotics. Independent variable
Crude (OR and 95% CI)
Adjusted (OR and 95% CI) Sleep-onset insomnia
Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.19
(0.99–1.43)
1.00 1.24
(1.04–1.49)
1.00 1.48 1.00 0.82
(1.23–1.78) (1.00–1.01) (0.77–0.86)
1.00 1.44 1.00 0.81
(1.20–1.73) (0.99–1.00) (0.76–0.86)
1.00 0.92 1.18
(0.73–1.17) (1.09–1.28)
1.00 0.89 0.92
(0.70–1.13) (0.63–1.33)
Maintenance insomnia Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.09
(0.92–1.30)
1.00 1.08
(0.91–1.29)
1.00 1.84 1.03 0.89
(1.55–2.19) (1.02–1.03) (0.85–0.94)
1.00 1.79 1.02 0.96
(1.50–2.13) (1.02–1.03) (0.91–1.01)
1.00 0.87 1.24
(0.70–1.09) (1.15–1.34)
1.00 0.96 1.11
(0.91–1.01) (0.78–1.58)
Early morning awakening insomnia Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.09
(0.91–1.30)
1.00 1.06
(0.88–1.27)
1.00 1.40 1.04 0.85
(1.15–1.65) (1.03–1.04) (0.80–0.89)
1.00 1.29 1.03 0.93
(1.07–1.55) (1.03–1.04) (0.88–0.98)
1.00 0.90 1.13
(0.72–1.14) (1.05–1.23)
1.00 0.92 1.05
(0.72–1.17) (0.73–1.52)
Dissatisfaction with sleep Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.78
(1.45–2.18)
1.00 1.78
(1.45–2.19)
1.00 1.27 1.01 0.95
(1.04–1.55) (1.00–1.01) (0.89–1.00)
1.00 1.26 1.00 0.95
(1.03–1.54) (1.00–1.00) (0.90–1.01)
1.00 1.15 1.28
(0.90–1.47) (1.18–1.40)
1.00 1.14 1.10
(0.89–1.46) (0.73–1.66)
Daytime impairment Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.33
(1.13–1.58)
1.00 1.41
(1.18–1.67)
1.00 1.63 0.98 0.97
(1.37–1.93) (0.98–0.99) (0.93–1.02)
1.00 1.68 0.98 0.94
(1.41–1.99) (0.98–0.99) (0.89–0.99)
1.00 0.89 1.27
(0.71–1.10) (1.18–1.36)
1.00 0.86 0.97
(0.69–1.08) (0.69–1.37) (continued on next page)
178
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179
Table 2 (continued) Independent variable
Crude (OR and 95% CI)
Adjusted (OR and 95% CI) DSM-IV insomnia cases
Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.36
(1.13–1.63)
1.00 1.37
(1.14–1.65)
1.00 1.65 1.01 0.91
(1.37–1.99) (1.00–1.01)* (0.86–0.96)
1.00 1.61 1.00 0.92
(1.34–1.95) (1.00–1.01)* (0.87–0.97)
1.00 0.95 1.27
(0.75–1.19) (1.17–1.37)
1.00 0.94 0.86
(0.74–1.19) (0.59–1.25)
Use of prescribed hypnotics Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.70
(1.36–2.13)
1.00 1.72
(1.36–2.17)
1.00 2.24 1.05 0.82
(1.78–2.83) (1.05–1.06) (0.77–0.87)
1.00 2.12 1.05 0.96
(1.67–2.70) (1.04–1.06) (0.90–1.02)
1.00 0.79 1.48
(0.59–1.06) (1.35–1.63)
1.00 0.81 1.03
(0.60–1.11) (0.63–1.69)
Abbreviations: OR, odds ratio; CI, confidence interval; DSM-IV, Diagnostic and Statistical Manual of Mental Disorders, Fourth Revision. If the OR was greater than 1.00, the result was considered significant. In the adjusted analyses it was controlled for all the other independent variables.
*
(mean difference of 3.3 years) than the 1999–2000 sample. Although this age difference might have influenced the results in the crude analyses, we did control for age as a continuous variable and for gender in the adjusted analyses. We corrected the estimate of the secular trend both for the discrepancy between the sample and the census of Norway and for the fact that the population on average had become approximately 1 year older between the 1999–2000 survey and the 2009–2010 survey. Thus the secular trend in insomnia confirmed by the adjusted analyses cannot be attributed to age differences between the samples. Based on the methodology we could not determine if the secular increase in insomnia symptoms reflected an increase in incidence or in persistence or duration of insomnia. Longitudinal studies have shown that there is a high persistence rate of insomnia, especially for women [53,54]. Persistent insomnia implies a higher demand for treatment in contrast to insomnia, which spontaneously remits. Some assets of our study also deserve to be mentioned. The questions used in the two surveys were identical and reflected both nocturnal sleeplessness and daytime impairment, which made our study unique compared to previous trend studies of insomnia prevalence [30–32]. Our study was based on representative samples of the adult Norwegian population. The samples were stratified by county, thus ensuring an optimal geographic representation. We also had reasonably large samples providing acceptable statistical power for the analyses [55]. In our analyses we controlled for basic demographic factors to ensure that findings concerning secular trends in insomnia prevalence did not capitalize on differences in basic population parameters across the two surveys. 5. Conclusions Our study findings suggest that the prevalence of several symptoms of insomnia have increased in the general adult population of Norway during the last decade. There is reason to be concerned about this development, as insomnia may cause and exacerbate a wide range of problems and disorders. The present development
also may turn out to be costly on a societal level, as the economic costs of insomnia are substantial [56]. We suggest that the emphasis on insomnia prevention [19] and on cost-effective interventions for insomnia [57] should be strengthened. Conflict of interest The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2013.10.009.
References [1] American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th ed. Washington, DC: American Psychiatric Association; 1994. [2] Liljenberg B, Almqvist M, Hetta J, Roos BE, Ågren H. Age and the prevalence of insomnia in adulthood. Eur J Psychiatry 1989;3:5–12. [3] Quera-Salva MA, Orluc A, Goldenberg F, Guilleminault C. Insomnia and use of hypnotics: a study of a French population. Sleep 1991;14:386–91. [4] Karacan I, Thornby JI, Williams RL. Sleep disturbance: a community survey. In: Guilleminault C, Lugaresi E, editors. Sleep/wake disorders: natural history, epidemiology, and long-term evolution. New York, NY: Raven Press; 1983. p. 37–60. [5] Ohayon MM. Epidemiology of insomnia: what we know and what we still need to learn. Sleep Med Rev 2002;6:97–111. [6] Pallesen S, Nordhus IH, Nielsen GH, Havik OE, Kvale G, Johnsen BH, et al. Prevalence of insomnia in the adult Norwegian population. Sleep 2001;24:771–9. [7] Zhang B, Wing YK. Sex differences in insomnia: a meta-analysis. Sleep 2006;29:85–93. [8] Ancoli-Israel S, Roth T. Characteristics of insomnia in the United States: results of the 1991 National Sleep Foundation survey. Sleep 1999;22:S347–53. [9] Ohayon MM. Epidemiological study on insomnia in the general population. Sleep 1996;19:S7–S15. [10] Ford DE, Kamerow DB. Epidemiologic study of sleep disturbance and psychiatric disorders. An opportunity for prevention. JAMA 1989;262:1479–84. [11] Gellis LA, Lichstein KL, Scarinci IC, Durrence HH, Taylor DJ, Bush AJ, et al. Socioeconomic status and insomnia. J Abnorm Psychol 2005;114:111–8. [12] Paine SJ, Gander PH, Harris R, Reid P. Who reports insomnia? Relationships with age, sex, ethnicity, and socioeconomic deprivation. Sleep 2004;27:1163–9. [13] Sivertsen B, Krokstad S, Øverland S, Mykletun A. The epidemiology of insomnia: associations with physical and mental health. The HUNT-2 study. J Psychosom Res 2009;67:109–16.
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179 [14] Kim K, Uchiyama M, Liu XC, Shibui K, Ohida T, Ogihara R, et al. Somatic and psychological complaints and their correlates with insomnia in the Japanese general population. Psychosom Med 2001;63:441–6. [15] Harvey AG. Insomnia: symptom or diagnosis? Clin Psychol Rev 2001;21:1037–59. [16] Baglioni C, Battagliese G, Feige B, Spiegelhalder K, Nissen C, Voderholzer U, et al. Insomnia as a predictor of depression: a meta-analytic evaluation of longitudinal epidemiological studies. J Affect Disord 2011;135:10–9. [17] Ribeiro JD, Pease JL, Gutierrez PM, Silva C, Bernert RA, Rudd MD, et al. Sleep problems outperform depression and hopelessness as cross-sectional and longitudinal predictors of suicidal ideation and behavior in young adults in the military. J Affect Disord 2012;136:743–50. [18] Sivertsen B, Øverland S, Bjorvatn B, Mæland JG, Mykletun A. Does insomnia predict sick leave? The Hordaland Health Study. J Psychosom Res 2009;66:67–74. [19] Sivertsen B, Øverland S, Neckelmann D, Glozier N, Krokstad S, Pallesen S, et al. The long-term effect of insomnia on work disability—the HUNT-2 historical cohort study. Am J Epidemiol 2006;163:1018–24. [20] Troxel WM, Buysse DJ, Matthews KA, Kip KE, Strollo PJ, Hall M, et al. Sleep symptoms predict the development of the metabolic syndrome. Sleep 2010;33:1633–40. [21] Quartana PJ, Wickwire EM, Klick B, Grace E, Smith MT. Naturalistic changes in insomnia symptoms and pain in temporomandibular joint disorder: a crosslagged panel analysis. Pain 2010;149:325–31. [22] Åkerstedt T, Fredlund P, Gillberg M, Jansson B. A prospective study of fatal occupational accidents—relationship to sleeping difficulties and occupational factors. J Sleep Res 2002;11:69–71. [23] Shekleton JA, Rogers NL, Rajaratnam SM. Searching for the daytime impairments of primary insomnia. Sleep Med Rev 2010;14:47–60. [24] Kottak CP. Primetime society: an anthropological analysis of television and culture, updated edition. Walnut Creek, CA: Left Coast Press; 2009. [25] Costa G. Shift work and occupational medicine: an overview. Occup Med 2003;53:83–8. [26] Suganuma N, Kikuchi T, Yanagi K, Yamamura S, Morishima H, Adachi H, et al. Using electronic media before sleep can curtail sleep time and result in selfperceived insufficient sleep. J Biol Rhythms 2007;5:204–14. [27] Rajaratnam SM, Arendt J. Health in a 24-h society. Lancet 2001;358:999–1005. [28] Manson JE, Skerrett PJ, Greenland P, VanItallie TB. The escalating pandemics of obesity and sedentary lifestyl—a call to action for clinicians. Arch Intern Med 2004;164:249–58. [29] Bin YS, Marshall NS, Glozier N. Secular trends in adult sleep duration: a systematic review. Sleep Med Rev 2012;16:223–30. [30] Ravan AR, Bengtsson C, Lissner L, Lapidus L, Björkelund C. Thirty-six-year secular trends in sleep duration and sleep satisfaction, and associations with mental stress and socioeconomic factors—results of the population study of women in Gothenburg, Sweden. J Sleep Res 2010;19:496–503. [31] Kronholm E, Partonen T, Laatikainen T, Peltonen M, Harma M, Hublin C, et al. Trends in self-reported sleep duration and insomnia-related symptoms in Finland from 1972 to 2005: a comparative review and re-analysis of Finnish population samples. J Sleep Res 2008;17:54–62. [32] Santos-Silva R, Bittencourt LR, Pires ML, de Mello MT, Taddei JA, Benedito-Silva AA, et al. Increasing trends of sleep complaints in the city of Sao Paulo, Brazil. Sleep Med 2010;11:520–4. [33] Salmon CT, Nichols JS. The next-birthday method of respondent selection. Public Opin Q 1983;47:270–6. [34] Pallesen S, Hetland J, Sivertsen B, Samdal O, Torsheim T, Nordhus IH. Time trends in sleep-onset difficulties among Norwegian adolescents: 1983–2005. Scand J Public Health 2008;36:889–95. [35] Simpson KRS, Meadows GN, Frances AJ, Patten SB. Is mental health in the Canadian population changing over time? Can J Psychiatry 2012;57:324–31.
179
[36] Härenstam A. Different development trends in working life and increasing occupational stress require new work environment strategies. Work 2005;24:261–77. [37] Sivertsen B, Øverland S, Pallesen S. Trends in timing of sleep in the general population of Norway: 1980–2000. Percept Mot Skills 2011;113:509–18. [38] Gellis LA, Lichstein KL. Sleep hygiene practices of good and poor sleepers in the United States: an Internet-based study. Behav Ther 2009;40:1–9. [39] Weaver E, Gradisar M, Dohnt H, Lovato B, Douglas P. The effect of presleep video-game playing on adolescent sleep. J Clin Sleep Med 2010;6:184–9. [40] Brunborg GS, Mentzoni RA, Molde H, Myrseth H, Skouveroe KJ, Bjorvatn B, et al. The relationship between media use in the bedroom, sleep habits and symptoms of insomnia. J Sleep Res 2011;20:569–75. [41] Van den Bulck J. Adolescent use of mobile phones for calling and for sending text messages after lights out: results from a prospective cohort study with a one-year follow-up. Sleep 2007;30:1220–3. [42] Higuchi S, Motohashi Y, Liu Y, Maeda A. Effects of playing a computer game using a bright display on presleep physiological variables, sleep latency, slow wave sleep and REM sleep. J Sleep Res 2005;14:267–73. [43] Carmelli D, Swan GE, Bliwise DL. Relationship of 30-year changes in obesity to sleep-disordered breathing in the Western Collaborative Group Study. Obes Res 2000;8:632–7. [44] Resta O, Barbaro MPF, Bonfitto P, Giliberti T, Depalo A, Pannacciulli N, et al. Low sleep quality and daytime sleepiness in obese patients without obstructive sleep apnoea syndrome. J Intern Med 2003;253:536–43. [45] Mykletun A, Knudsen AK, Mathiesen KS. Psychiatric disorders in Norway: a public health perspective [in Norwegian]. Oslo, Norway: Norwegian Institute of Public Health; 2009. [46] Bliwise DL, Ansari FP, Straight LB, Parker KP. Age changes in timing and 24-h distribution of self-reported sleep. Am J Geriatr Psychiatry 2005;13:1077–82. [47] Klerman EB, Davis JB, Duffy JF, Dijk DJ, Kronauer RE. Older people awaken more frequently but fall back asleep at the same rate as younger people. Sleep 2004;27:793–8. [48] Catala E, Reig E, Artes M, Aliaga L, Lopez JS, Segu JL. Prevalence of pain in the Spanish population: telephone survey in 5000 homes. Eur J Pain 2002;6:133–40. [49] Bixler EO, Vgontzas AN, Ten Have T, Tyson K, Kales A. Effects of age on sleep apnea in men I. Prevalence and severity. Am J Respir Crit Care Med 1998;157:144–8. [50] Omvik S, Pallesen S, Bjorvatn B, Sivertsen B, Havik OE, Nordhus IH. Patient characteristics and predictors of sleep medication use. Int Clin Psychopharmacol 2010;25:91–100. [51] Søgaard AJ, Selmer R, Bjertness E, Thelle D. The Oslo Health Study: the impact of self-selection in a large, population-based survey. Int J Equity Health 2004;3:3. [52] Torvik FA, Rognmo K, Tambs K. Alcohol use and mental distress as predictors of non-response in a general population health survey: the HUNT study. Soc Psychiatry Psychiatr Epidemiol 2012;47:805–16. [53] Morin CM, Bélanger L, LeBlanc M, Ivers H, Savard J, Espie CA, et al. The natural history of insomnia: a population-based 3-year longitudinal study. Arch Intern Med 2009;169:447–53. [54] Zhang J, Lam SP, Li SX, Yu MW, Li AM, Ma RC, et al. Long-term outcomes and predictors of chronic insomnia: a prospective study in Hong Kong Chinese adults. Sleep Med 2012;13:455–62. [55] Cohen J. Statistical power analysis for the behavioral sciences. 2nd ed. Hillsdale, NJ: Lawrence Erlbaum Associates Publishers; 1988. [56] Wade AG. The societal costs of insomnia. Neuropsychiatry Dis Treat 2011;7:1–18. [57] Bjorvatn B, Fiske E, Pallesen S. A self-help book is better than sleep hygiene advice for insomnia: a randomized controlled comparative study. Scand J Psychol 2011;52:580–5.
Contents lists available at ScienceDirect
Sleep Medicine journal homepage: www.elsevier.com/locate/sleep
Original Article
A 10-year trend of insomnia prevalence in the adult Norwegian population Ståle Pallesen a,b,⇑, Børge Sivertsen c,d,e, Inger Hilde Nordhus b,f, Bjørn Bjorvatn b,g a
Department of Psychosocial Science, University of Bergen, P.O. Box 7807, N-5020 Bergen, Norway Norwegian Competence Center for Sleep Disorders, Jonas Lies vei 65, 5021 Bergen, Norway c Department of Public Mental Health, Norwegian Institute of Public Health, Kalfarveien 31, 5018 Bergen, Norway d Uni Health, Uni Research Bergen, P.O. Box 7810, N-5020 Bergen, Norway e Department of Psychiatry, Helse Fonna HF, P.O. Box 2170, N-5504 Haugesund, Norway f Department of Clinical Psychology, University of Bergen, P.O. Box 7807, N-5020 Bergen, Norway g Department of Public Health and Primary Health Care, University of Bergen, P.O. Box 7804, N-5020 Bergen, Norway b
a r t i c l e
i n f o
Article history: Received 16 March 2013 Received in revised form 11 October 2013 Accepted 15 October 2013 Available online 1 December 2013 Keywords: Sleep Insomnia Secular Trend Prevalence Epidemiology
a b s t r a c t Objective: We aimed to investigate the 10-year trend in the prevalence of insomnia symptoms, insomnia cases, and use of hypnotic agents in the adult Norwegian population. Methods: Data from two representative surveys assessing identical insomnia symptoms in the adult population of Norway, one conducted in 1999–2000 (N = 2001) and one conducted in 2009–2010 (N = 2000), were compared. Results: Controlling for basic demographic variables, significant increases were found over the 10-year study period in the prevalence of sleep-onset insomnia from 13.1% to 15.2%, dissatisfaction with sleep from 8.2% to 13.6%, daytime impairment from 14.8% to 18.8%, Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) insomnia cases from 11.9% to 15.5%, and hypnotic agent use from 6.9% to 11.1%. No secular trend was found for maintenance insomnia or for early morning awakening insomnia. Across the two surveys, women reported a higher prevalence of insomnia than men. Age was positively associated with the prevalence of nocturnal sleep problems and use of hypnotic agents but was inversely associated with daytime impairment. Individuals with low socioeconomic status (SES) reported a higher prevalence of several insomnia symptoms. Conclusions: Insomnia seems to be on the rise in the general adult population, which gives reason for concern. Prevention of insomnia and cost-effective interventions should receive higher priority in the future. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction Insomnia is characterized by problems initiating or maintaining sleep or nonrestorative sleep, which leads to one or more forms of daytime impairment [1]. Epidemiologic studies have reported a wide range of insomnia prevalence, from approximately 2% [2] to 48% [3], reflecting different ways of defining and assessing insomnia and differences in study samples [4]. This range in prevalence makes comparisons of findings across studies problematic. When insomnia is defined according to formal diagnostic systems, the range of prevalence becomes more narrow and varies between approximately 6% [5] and 12% [6].
⇑ Corresponding author. Address: Department of Psychosocial Science, Faculty of Psychology, Christiesgt. 12, 5015 Bergen, Norway. Tel.: +47 55588842; fax: +47 55589879. E-mail address: [email protected] (S. Pallesen). 1389-9457/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sleep.2013.10.009
Although there are discrepancies between studies of prevalence rates, there seems to be greater consensus about the demographic factors associated with insomnia across studies. Most studies report female preponderance [7], an increasing prevalence with age [8,9], an association between insomnia and low socioeconomic status (SES) [10–12], and an elevated insomnia prevalence in individuals reporting psychiatric [13] and somatic [14] symptoms compared to healthy control participants. Previous perspectives typically have implied that insomnia represented a consequence or a symptom of other disorders [15]. However, newer perspectives based on prospective or longitudinal studies indicate that insomnia can lead to or exacerbate several problematic situations or disorders, such as depression [16], suicidal ideations [17], sick leave [18], disability pension [19], metabolic syndrome [20], pain [21], work accidents [22], and impaired cognition [23]. During the last decades many societal changes that may influence sleep have occurred, such as an expansion of television
174
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179
broadcasts [24]; an increase in nonstandard working hours [25]; an increase in use of electronic devices, including computers, smart phones, video games, among others [26]; the establishment of a 24-h society [27]; and an increase of the proportion of the population who are overweight or obese [28]. However, a systematic review of secular trends in adult sleep duration in 15 countries from the 1960s until the 2000s showed an increase in sleep duration in seven countries but a decrease in six countries, leading the authors to conclude that there has not been any consistent decrease in self-reported sleep duration of adults from the 1960s to the 2000s [29]. Nevertheless, some secular trend studies of insomnia symptoms suggest a worsening of sleep over time. In a study of women in Sweden, cohort comparisons of participants ages 38 or 50 years between 1968–1969 and 2004–2005 suggested that sleep problems had almost doubled in both age groups, whereas the use of sleep medication remained unchanged since 1968 [30]. Data from seven independent cross-sectional representative population surveys performed between 1972 and 2005 in Finland revealed an increase in both occasional and chronic insomnia symptoms across the 33-year period [31]. Comparisons of results from three representative cross-sectional studies of inhabitants of São Paulo, Brazil, conducted in 1987, 1995, and 2007, respectively, showed an approximate 2-fold increase in the proportions reporting difficulty initiating sleep, difficulty maintaining sleep, and early morning awakening over the 20-year time span [32]. However, more studies on the issue of secular trends in insomnia are needed, especially as the number of previous studies is few. In addition, some of the studies only focused on women [30] and some only used global sleep questions that do not discriminate between different insomnia symptoms [30,31]; to our knowledge no previous trend study has reported on daytime impairment. The main goal of our study was to investigate if a change in the prevalence of insomnia symptoms occurred over a 10-year period in the adult Norwegian population. To achieve our goal, we compared survey data collected 10 years apart in representative samples of the adult Norwegian population.
2. Methods 2.1. Participants In 1999–2000 a total of 2001 randomly selected adults aged 18 years and older (1091 women and 910 men) participated in a telephone survey in which they answered questions related to demography and sleep among other variables. Exactly ten years later in 2009–2010, a similar telephone survey was conducted, which included a total of 2000 randomly selected adults (1039 women and 961 men) who answered identical questions. There were no significant differences between the surveys in the gender distribution (v2 = 2.6; df = 1; P > .05). The mean unweighted age of the sample in 1999–2000 was 44.7 years (standard deviation, 15.6), and 48.0 (standard deviation, 17.4) in 2009–2010 (t = 6.4; df = 3951; P < .01). The census data of Norway show that the mean age of adults aged 18 years or older was 46.6 years in 2000 and 47.5 years in 2010, respectively. In 1999–2000, 9.6% of the sample had no education subsequent to mandatory schooling, while 30.3% had one to 3 years, 32.2% had 4–6 years, and 27.8% had more than 6 years of education subsequent to mandatory schooling, respectively. The corresponding figures in the 2009–2010 sample were 8.4%, 33.9%, 31.0%, and 26.8%, respectively (v2 = 6.5, df = 3, P > .05). The numbers of individuals in the age categories (18– 29 years, 30–44 years, 45–59 years, and P60 years) were 456, 572, 456, and 517, respectively, in the 1999–2000 sample. The corresponding figures for the 2009–2010 sample were 378, 576, 518 and 528, respectively.
2.2. Materials In addition to demographic and other background information (e.g., age, gender, education, place of residence, family income), the participants were asked to answer the following questions about their sleep: (1) After you turn off the lights, how long does it normally take you to fall asleep? (2) Do you wake up from sleep before the final morning awakening? If so, what is the total time during the night you are awake? (3) Do you wake up at least half an hour earlier than you wish to? If so, how often has this happened during the previous month (Never, 1–4 days, 5–10 days, 11–20 days, >20 days)? (4) How satisfied are you with your present sleep (very satisfied, somewhat satisfied, neither satisfied nor unsatisfied, somewhat unsatisfied, very unsatisfied)? (5) Is your sleep so poor that it affects your daily activities or duties? If so, how often has this happened during the previous month (Never, 1–4 days, 5–10 days, 11–20 days, more than 20 days)? (6) Do you use sleeping pills prescribed by a medical doctor? If so, how often has this happened during the previous month (Never, 1–4 days, 5–10 days, 11–20 days, more than 20 days)? All questions pertained to the previous month. We also asked two questions about insomnia comorbidity: (1) During the last month, have you had any physical ailment or illnesses (no/yes)? (2) During the last month, have experienced any emotional or psychologic problems (no/yes)? 2.3. Procedure The 1999–2000 survey was part of a telephone omnibus conducted by an opinion-research institute (Norsk Respons). Random telephone numbers were drawn from the customer list of the largest telephone company in Norway covering approximately 98% of all Norwegian households. To ensure a random sample, the next birthday technique was employed, which involved asking to speak with the adult household member who has the next birthday [33]. Half of the interviews were conducted during the first 2 weeks of December 1999 and the other half during the first 2 weeks of June 2000. The response rate was based on the number of those who answered the telephone, which was 56.9%. The results from that survey have been previously published [6]. The 2009–2010 survey also was conducted by an opinion-research institute (Respons Analyse; former Norsk Respons). Half of the interviews were conducted during the first 2 weeks of December 2009 and the other half during the first 2 weeks of June 2010. For the two waves in the 2009–2010 survey, 3000 inhabitants of Norway aged 18 years and older, who were randomly drawn from Norwegian Population Registry, were sent a letter informing them that they might receive a phone call to be invited to participate in a telephone survey about sleep. The response rate was based on the number of those who answered the telephone for the 2009–2010 survey, which was 64.9%. Because no link was made between the responses and the name list or between the responses and the phone numbers, the data were anonymously collected according to Norwegian legislation. For both the 1999–2000 survey and the 2009–2010 survey, no more calls were made when the aim of recruiting 1000 respondents each season was met. In addition, the samples were stratified by the number of inhabitants of all counties for both surveys, thus the census of Norway in county population comprised a sampling criterion. When the proportional number of respondents for each county was met, further recruitment of respondents from that county was terminated. For both surveys, the only inclusion criterion was age (P18 years); no exclusion criteria were employed. Compared to the census of Norway individuals in the youngest (18–29 years) and oldest (P60 years) age groups and men were underrepresented in both the 1999–2000 survey and in the 2009–2010 survey. In the analyses, we adjusted for this variable
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179
by weighing the subgroups according to age and gender of the census of Norway. A weight of less than two was used for all cases. The fees to the opinion research institutes were covered by a grant from the Norwegian Competence Center for Sleep Disorders, funding from the University of Bergen, and a grant from the Norwegian Research Council. Length of education and family income were used as proxies for SES by transforming the scores for those two items into z scores and adding them to create a single composite variable. This process was separately performed for the 1999–2000 and the 2009–2010 survey. Negative z scores indicated an SES below mean, whereas positive z scores indicated a status above mean. For region the five most northern counties of Norway were defined as Northern (62°–71° north) and the other counties were defined as Southern (58°–62° north). Insomnia inclusion criterion 1 of the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) [1], was met if one of the following three subcriteria were met: (1) mean sleep-onset latency exceeding 30 min, (2) mean wake time after sleep onset exceeding 30 min, or (3) waking up at least 30 min earlier than the individual preferred more than 10 days per month. Insomnia inclusion criterion 2 was considered fulfilled if one of the following two subcriteria were met: (a) reporting being somewhat or very unsatisfied with present sleep; or (b) reporting sleep so poor that it affected daily activities or duties more than 4 days per month. The DSM-IV inclusion criteria for insomnia were met if criterion 1 and criterion 2 were both fulfilled and suggested DSM-IV insomnia cases. Because all data were anonymously collected, both surveys were exempted from review by the Ethics Board (The Regional Committee for Medical Research Ethics in Western Norway). 2.4. Statistical analyses Data analyses were conducted by the IBMÓ SPSS Statistics, version 19. All prevalence figures and confidence intervals (CIs) were calculated by weighting the cases according to the population distribution of gender and age to correct for potential divergence between the sample and the distribution of age and gender in the general population of Norway. Weighted prevalence and 95% CIs for all the single insomnia symptoms and for DSM-IV insomnia cases and for use of hypnotics were separately calculated for the 1999–2000 and the 2009–2010 survey. Results also were broken down by gender and age groups (18–29 years, 30–44 years, 45–59 years, and P60 years). A weighted logistic regression analysis was used to investigate if sociodemographic variables (e.g., year, gender, age, SES, region) were related to insomnia and use of hypnotic agents. In step 1, year, gender, age, SES, and region were entered as independent variables, whereas the interaction term year gender was entered in step 2 to investigate if potential secular changes in insomnia differed between the genders. In the logistic regression analyses, age and SES were entered as continuous variables, whereas year, gender, and region were entered as dichotomized variables. Logistic regression analyses, in which only single dependent variable was included (crude), also were conducted. Results from the logistic regression analyses were considered significant when the confidence interval did not include 1.00. To investigate any secular change in somatic and psychiatric comorbidity, we performed v2 tests to determine if the proportion of the samples reporting such symptoms differed between the 1999–2000 and 2009–2010 samples. 3. Results Table 1 shows the prevalence of the different insomnia symptoms including the 95% CIs, broken down by gender and age
175
groups. Table 2 presents the results from the logistic regression analyses. From 1999–2000 to the time of the second survey in 2009–2010, the prevalence changed as follows (reported odds ratios [ORs] are from the adjusted regression analyses): sleep-onset insomnia changed from 13.1% to 15.2% (OR, 1.24 [95% CI, 1.04– 1.49]); maintenance insomnia changed from 16.3% to 17.6% (OR, 1.08 [95% CI, 0.91–1.29]); early morning awakening insomnia changed from 14.0% to 15.0% (OR, 1.06 [95% CI, 0.88–1.27]); dissatisfaction with sleep changed from 8.2% to 13.6% (OR, 1.78 [95% CI, 1.45–2.19]); daytime impairment changed from 14.8% to 18.8% (OR, 1.41 [95% CI, 1.18–1.67]); DSM-IV insomnia cases changed from 11.9% to 15.5% (OR, 1.37 [95% CI, 1.14–1.65]); and hypnotic use changed from 6.9% to 11.1% (OR, 1.72 [95% CI, 1.36–2.17]). Across the two surveys, women reported a higher prevalence of insomnia than men. Age was positively associated with the prevalence of nocturnal sleep problems and use of hypnotic agents, but it was inversely associated with daytime impairment. Individuals with low SES reported a higher prevalence of several insomnia symptoms. We found no secular changes for physical ailment or illnesses (v2 = 0.33; df = 1; P > .05) or for emotional or psychologic concerns (v2 = 3.68; df = 1; P > .05).
4. Discussion The main question that we addressed in our study concerned a possible secular change in the insomnia prevalence in Norway. Our data showed that the prevalence of sleep-onset insomnia, dissatisfaction with sleep, daytime impairment, DSM-IV insomnia cases, and use of prescribed hypnotic agents had all increased during the 10-year period between 1999–2000 and 2009–2010, whereas no significant secular trend was found for the prevalence of maintenance insomnia and early morning awakening insomnia. Thus overall the findings of our study corresponded well with previous trend studies of insomnia prevalence [30–32,34]. Our findings might suggest a possible secular trend in the willingness to report health problems [35], though it is doubtful that this factor explains large proportions of the changes in insomnia prevalence. A more plausible explanation relates to working life, in which studies suggest an increase in occupational stress [36] and in shift work [25] over the years. Another possible explanation involves worsening of sleep habits over time. Recently we reported data showing that the discrepancy between sleep times during weekdays and weekends has increased over the last decades in Norway [37], which is a factor that might contribute to sleep problems. Another potential contributing factor to the secular trend in insomnia reported here comprises the sharp increase in the availability and use of electronic devices, such as mobile phones, video game consoles, computers and tablets [26], as their potential for disturbing sleep has been widely recognized [38,39]. Previously we reported that the use of such devices in the bedroom was associated with delayed bedtimes [40] and other studies have shown that the use of such devices is related to daytime tiredness [41] and prolonged sleeponset latency [42]. The secular increase in body mass index of the general population also may explain the rise in insomnia prevalence, as obesity and overweight can cause sleep-disordered breathing [43] and impaired sleep quality [44]. Because we did not collect data specifically concerning the aforementioned factors, we were precluded from investigating if these factors actually were related to the secular changes in insomnia that we reported in our present study. Thus future studies should more explicitly address these issues. The secular increase found for several insomnia symptoms did not seem to be related to somatic and psychiatric comorbidity, as no secular change concerning these variables was found in our
176
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179
Table 1 Prevalence (%) and 95% confidence intervals for the different insomnia symptoms broken down by age and gender for the 1999/2000 survey and the 2009/2010 survey. Men
Women
1999/2000
2009/2010
1999/2000
2009/2010
Sleep-onset insomnia 18–29 y 30–44 y 45–59 y P60 y
% (95% CI) 16.1 (10.0–22.2) 7.1 (4.3–10.0) 5.0 (2.2–7.8) 13.7 (8.1–19.3)
% (95% CI) 22.5 (16.0–29.0) 10.3 (6.4–14.1) 6.7 (3.4–10.0) 16.2 (11.6–20.8)
% (95% CI) 18.0 (12.4–23.7) 9.5 (6.5–12.5) 13.2 (9.2–17.2) 21.7 (15.1–28.2)
% (95% CI) 20.5 (14.2–26.8) 12.7 (8.8–16.6) 13.6 (9.4–17.8) 22.8 (17.1–28.4)
Maintenance insomnia 18–29 y 30–44 y 45–59 y P60 y
10.5 (5.4–15.6) 7.5 (4.5–10.4) 7.5 (4.2–19.9) 22.6 (15.7–29.5)
5.6 (2.0–9.3) 11.1 (7.1–15.1) 12.5 (8.1–16.9) 19.0 (14.1–24.0)
12.0 12.2 17.1 30.0
12.4 19.4 21.7 27.9
Early morning awakening insomnia 18–29 y 30–44 y 45–59 y P60 y
2.1 ( 0.3 to 4.5) 7.8 (4.8–10.8) 14.6 (10.1–19.2) 24.0 (17.0–31.0)
3.1 (0.4–5.9) 10.3 (6.4–14.1) 16.1 (11.2–20.9) 19.0 (14.1–24.0)
4.4 (1.4–7.4) 7.9 (5.1–10.7) 15.3 (11.1–19.5) 31.2 (23.9–38.5)
7.5 (3.4–11.6) 14.4 (10.3–18.6) 20.9 (15.9–25.9) 22.8 (17.1–28.4)
Dissatisfaction with sleep 18–29 y 30–44 y 45–59 y P60 y
10.5 (5.4–15.6) 6.5 (3.7–9.3) 5.4 (2.5–8.3) 5.5 (1.7–9.2)
11.3 (6.3–16.2) 11.9 (7.8–16.0) 9.8 (5.9–13.8) 11.3 (7.4–15.3)
7.7 (3.8–11.5) 8.2 (5.3–11.0) 5.0 (2.4–7.5) 10.0 (4.9–14.2)
8.7 (4.3–13.1) 15.1 (11.0–19.3) 17.8 (13.1–22.5) 14.0 (9.3–18.6)
Daytime impairment 18–29 y 30–44 y 45–59 y P60 y
17.5 (11.2–23.8) 12.3 (8.6–16.0) 11.3 (7.3–15.3) 3.4 (0.4–6.4)
22.5 (16.0–29.0) 17.3 (12.5–22.1) 13.0 (8.5–17.4) 8.1 (4.7–11.5)
23.0 17.1 13.9 14.0
(16.8–29.1) (13.3–21.0) (9.8–18.0) (8.5–19.5)
27.3 26.1 21.7 16.3
(20.4–34.3) (20.9–31.2) (16.4–26.8) (11.3–21.3)
DSM-IV insomnia cases 18–29 y 30–44 y 45–59 y P60 y
12.6 (7.1–18.1) 5.8 (3.2–8.5) 8.4 (4.8–11.9) 6.9 (2.7–11.0)
11.9 11.9 10.7 12.2
10.4 11.1 10.3 19.8
(5.9–14.8) (7.9–14.4) (6.7–13.9) (13.5–26.0)
12.4 16.6 20.2 16.7
(7.3–17.6) (12.2–20.9) (15.2–25.1) (11.7–21.8)
Use of prescribed hypnotics 18–29 y 30–44 y 45–59 y P60 y
0.0 (0.0–0.0) 1.6 (0.2–3.0) 4.2 (1.6–6.7) 11.6 (6.4–16.9)
3.8 (0.8–6.7) 2.9 (0.8–5.0) 3.6 (1.1–6.0) 17.8 (13.0–22.6)
(6.8–16.9) (7.8–16.0) (6.7–14.8) (8.0–16.3)
(7.3–16.8) (8.9–15.6) (12.7–21.5) (22.7–37.2)
2.2 (0.1–4.3) 3.5 (1.6–5.4) 8.9 (5.6–12.3) 19.1 (12.9–25.3)
(7.3–17.8) (14.7–24.0) (16.6–26.8) (21.9–34.0)
3.1 (0.4–5.8) 6.3 (3.5–9.2) 17.1 (12.4–21.7) 27.9 (21.9–34.0)
Abbreviations: CI, confidence interval; y, years; DSM-IV, Diagnostic and Statistical Manual of Mental Disorders, Fourth Revision.
study. This finding is further corroborated with other studies that reported no increase in psychiatric problems in the Norwegian population during the last decades [45]. The fact that we also found an increase in the use of hypnotic agents does support the overall notion of a secular increase of insomnia in the general population. Although most insomnia symptoms did increase with time, symptoms of maintenance insomnia and early morning awakening insomnia did not for unknown reasons. Compared to men, women had a higher prevalence of all insomnia symptoms, DSM-IV insomnia cases, and use of prescribed hypnotic agents. These results are consistent with previous studies [7]. Age was positively related to insomnia, especially insomnia occurring after sleep onset. This finding most likely reflects a shortening of the sleep-wake rhythm with age [46] and more arousals during sleep with increasing age [47], as well an increase in somatic conditions such as pain [48] and sleep disorders such as obstructive sleep apnea [49]. Age was inversely associated with daytime impairment, which might reflect that younger individuals have a greater sleep debt than older individuals and that elderly individuals have fewer scheduled responsibilities [6]. Our finding that age was positively associated with hypnotic agent use correlates well with previous studies [50]. SES was negatively associated with sleep-onset insomnia, early morning awakening insomnia, daytime impairment, and DSM-IV insomnia cases in our study. These findings are consistent with previous studies [9,10] and suggest that disadvantageous social factors interfere with sleep [6]. Although we previously found that geographic region was related to the
use of hypnotic agents (6), geographic region was not related to any of the dependent variables in our study based on the adjusted analyses, indicating that insomnia symptoms showed an evenly geographic distribution in Norway. Results from the crude regression analyses suggested that the secular development of insomnia did vary by gender; however, these results did not remain significant in the adjusted analyses. 4.1. Methodologic considerations Some limitations of our study should be noted. In the 1999– 2000 survey, the sleep questions were part of a general telephone omnibus, whereas the respondents participating in the 2009–2010 survey received a letter informing them that they might receive a phone call asking them to participate in a telephone survey about sleep. Thus the risk for self-selection (e.g., in respondents with sleep problems) may be greater for the last survey compared to the first survey [51]. The response rate was 56.9% in the 1999– 2000 survey, whereas it was 64.9% in the 2009–2010 survey. Because nonresponse is found to be associated with pathology [52], the proportion of respondents with different forms of pathology might have been higher in the latter survey than in the former, which might have led to inflated insomnia estimates. It also should be noted that the insomnia symptoms assessed in our study do not exclusively pertain to insomnia sleep disorder but also might reflect a wider range of sleep disorders and other disorders known to affect sleep [1]. The 2009–2010 sample was significantly older
177
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179
Table 2 Results from the regression analyses (odds ratio) and 95% confidence intervals in which year, gender, age, socioeconomic status, region, and the interaction term year gender are regressed on different insomnia symptoms (e.g., sleep-onset insomnia, maintenance insomnia, early morning awakening insomnia, dissatisfaction with sleep, daytime impairment); Diagnostic and Statistical Manual of Mental Disorders, Fourth Revision, insomnia cases; and use of prescribed hypnotics. Independent variable
Crude (OR and 95% CI)
Adjusted (OR and 95% CI) Sleep-onset insomnia
Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.19
(0.99–1.43)
1.00 1.24
(1.04–1.49)
1.00 1.48 1.00 0.82
(1.23–1.78) (1.00–1.01) (0.77–0.86)
1.00 1.44 1.00 0.81
(1.20–1.73) (0.99–1.00) (0.76–0.86)
1.00 0.92 1.18
(0.73–1.17) (1.09–1.28)
1.00 0.89 0.92
(0.70–1.13) (0.63–1.33)
Maintenance insomnia Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.09
(0.92–1.30)
1.00 1.08
(0.91–1.29)
1.00 1.84 1.03 0.89
(1.55–2.19) (1.02–1.03) (0.85–0.94)
1.00 1.79 1.02 0.96
(1.50–2.13) (1.02–1.03) (0.91–1.01)
1.00 0.87 1.24
(0.70–1.09) (1.15–1.34)
1.00 0.96 1.11
(0.91–1.01) (0.78–1.58)
Early morning awakening insomnia Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.09
(0.91–1.30)
1.00 1.06
(0.88–1.27)
1.00 1.40 1.04 0.85
(1.15–1.65) (1.03–1.04) (0.80–0.89)
1.00 1.29 1.03 0.93
(1.07–1.55) (1.03–1.04) (0.88–0.98)
1.00 0.90 1.13
(0.72–1.14) (1.05–1.23)
1.00 0.92 1.05
(0.72–1.17) (0.73–1.52)
Dissatisfaction with sleep Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.78
(1.45–2.18)
1.00 1.78
(1.45–2.19)
1.00 1.27 1.01 0.95
(1.04–1.55) (1.00–1.01) (0.89–1.00)
1.00 1.26 1.00 0.95
(1.03–1.54) (1.00–1.00) (0.90–1.01)
1.00 1.15 1.28
(0.90–1.47) (1.18–1.40)
1.00 1.14 1.10
(0.89–1.46) (0.73–1.66)
Daytime impairment Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.33
(1.13–1.58)
1.00 1.41
(1.18–1.67)
1.00 1.63 0.98 0.97
(1.37–1.93) (0.98–0.99) (0.93–1.02)
1.00 1.68 0.98 0.94
(1.41–1.99) (0.98–0.99) (0.89–0.99)
1.00 0.89 1.27
(0.71–1.10) (1.18–1.36)
1.00 0.86 0.97
(0.69–1.08) (0.69–1.37) (continued on next page)
178
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179
Table 2 (continued) Independent variable
Crude (OR and 95% CI)
Adjusted (OR and 95% CI) DSM-IV insomnia cases
Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.36
(1.13–1.63)
1.00 1.37
(1.14–1.65)
1.00 1.65 1.01 0.91
(1.37–1.99) (1.00–1.01)* (0.86–0.96)
1.00 1.61 1.00 0.92
(1.34–1.95) (1.00–1.01)* (0.87–0.97)
1.00 0.95 1.27
(0.75–1.19) (1.17–1.37)
1.00 0.94 0.86
(0.74–1.19) (0.59–1.25)
Use of prescribed hypnotics Year 1999/2000 2009/2010 Gender Men Women Age Socioeconomic status Region Southern Norway Northern Norway Year gender
1.00 1.70
(1.36–2.13)
1.00 1.72
(1.36–2.17)
1.00 2.24 1.05 0.82
(1.78–2.83) (1.05–1.06) (0.77–0.87)
1.00 2.12 1.05 0.96
(1.67–2.70) (1.04–1.06) (0.90–1.02)
1.00 0.79 1.48
(0.59–1.06) (1.35–1.63)
1.00 0.81 1.03
(0.60–1.11) (0.63–1.69)
Abbreviations: OR, odds ratio; CI, confidence interval; DSM-IV, Diagnostic and Statistical Manual of Mental Disorders, Fourth Revision. If the OR was greater than 1.00, the result was considered significant. In the adjusted analyses it was controlled for all the other independent variables.
*
(mean difference of 3.3 years) than the 1999–2000 sample. Although this age difference might have influenced the results in the crude analyses, we did control for age as a continuous variable and for gender in the adjusted analyses. We corrected the estimate of the secular trend both for the discrepancy between the sample and the census of Norway and for the fact that the population on average had become approximately 1 year older between the 1999–2000 survey and the 2009–2010 survey. Thus the secular trend in insomnia confirmed by the adjusted analyses cannot be attributed to age differences between the samples. Based on the methodology we could not determine if the secular increase in insomnia symptoms reflected an increase in incidence or in persistence or duration of insomnia. Longitudinal studies have shown that there is a high persistence rate of insomnia, especially for women [53,54]. Persistent insomnia implies a higher demand for treatment in contrast to insomnia, which spontaneously remits. Some assets of our study also deserve to be mentioned. The questions used in the two surveys were identical and reflected both nocturnal sleeplessness and daytime impairment, which made our study unique compared to previous trend studies of insomnia prevalence [30–32]. Our study was based on representative samples of the adult Norwegian population. The samples were stratified by county, thus ensuring an optimal geographic representation. We also had reasonably large samples providing acceptable statistical power for the analyses [55]. In our analyses we controlled for basic demographic factors to ensure that findings concerning secular trends in insomnia prevalence did not capitalize on differences in basic population parameters across the two surveys. 5. Conclusions Our study findings suggest that the prevalence of several symptoms of insomnia have increased in the general adult population of Norway during the last decade. There is reason to be concerned about this development, as insomnia may cause and exacerbate a wide range of problems and disorders. The present development
also may turn out to be costly on a societal level, as the economic costs of insomnia are substantial [56]. We suggest that the emphasis on insomnia prevention [19] and on cost-effective interventions for insomnia [57] should be strengthened. Conflict of interest The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2013.10.009.
References [1] American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th ed. Washington, DC: American Psychiatric Association; 1994. [2] Liljenberg B, Almqvist M, Hetta J, Roos BE, Ågren H. Age and the prevalence of insomnia in adulthood. Eur J Psychiatry 1989;3:5–12. [3] Quera-Salva MA, Orluc A, Goldenberg F, Guilleminault C. Insomnia and use of hypnotics: a study of a French population. Sleep 1991;14:386–91. [4] Karacan I, Thornby JI, Williams RL. Sleep disturbance: a community survey. In: Guilleminault C, Lugaresi E, editors. Sleep/wake disorders: natural history, epidemiology, and long-term evolution. New York, NY: Raven Press; 1983. p. 37–60. [5] Ohayon MM. Epidemiology of insomnia: what we know and what we still need to learn. Sleep Med Rev 2002;6:97–111. [6] Pallesen S, Nordhus IH, Nielsen GH, Havik OE, Kvale G, Johnsen BH, et al. Prevalence of insomnia in the adult Norwegian population. Sleep 2001;24:771–9. [7] Zhang B, Wing YK. Sex differences in insomnia: a meta-analysis. Sleep 2006;29:85–93. [8] Ancoli-Israel S, Roth T. Characteristics of insomnia in the United States: results of the 1991 National Sleep Foundation survey. Sleep 1999;22:S347–53. [9] Ohayon MM. Epidemiological study on insomnia in the general population. Sleep 1996;19:S7–S15. [10] Ford DE, Kamerow DB. Epidemiologic study of sleep disturbance and psychiatric disorders. An opportunity for prevention. JAMA 1989;262:1479–84. [11] Gellis LA, Lichstein KL, Scarinci IC, Durrence HH, Taylor DJ, Bush AJ, et al. Socioeconomic status and insomnia. J Abnorm Psychol 2005;114:111–8. [12] Paine SJ, Gander PH, Harris R, Reid P. Who reports insomnia? Relationships with age, sex, ethnicity, and socioeconomic deprivation. Sleep 2004;27:1163–9. [13] Sivertsen B, Krokstad S, Øverland S, Mykletun A. The epidemiology of insomnia: associations with physical and mental health. The HUNT-2 study. J Psychosom Res 2009;67:109–16.
S. Pallesen et al. / Sleep Medicine 15 (2014) 173–179 [14] Kim K, Uchiyama M, Liu XC, Shibui K, Ohida T, Ogihara R, et al. Somatic and psychological complaints and their correlates with insomnia in the Japanese general population. Psychosom Med 2001;63:441–6. [15] Harvey AG. Insomnia: symptom or diagnosis? Clin Psychol Rev 2001;21:1037–59. [16] Baglioni C, Battagliese G, Feige B, Spiegelhalder K, Nissen C, Voderholzer U, et al. Insomnia as a predictor of depression: a meta-analytic evaluation of longitudinal epidemiological studies. J Affect Disord 2011;135:10–9. [17] Ribeiro JD, Pease JL, Gutierrez PM, Silva C, Bernert RA, Rudd MD, et al. Sleep problems outperform depression and hopelessness as cross-sectional and longitudinal predictors of suicidal ideation and behavior in young adults in the military. J Affect Disord 2012;136:743–50. [18] Sivertsen B, Øverland S, Bjorvatn B, Mæland JG, Mykletun A. Does insomnia predict sick leave? The Hordaland Health Study. J Psychosom Res 2009;66:67–74. [19] Sivertsen B, Øverland S, Neckelmann D, Glozier N, Krokstad S, Pallesen S, et al. The long-term effect of insomnia on work disability—the HUNT-2 historical cohort study. Am J Epidemiol 2006;163:1018–24. [20] Troxel WM, Buysse DJ, Matthews KA, Kip KE, Strollo PJ, Hall M, et al. Sleep symptoms predict the development of the metabolic syndrome. Sleep 2010;33:1633–40. [21] Quartana PJ, Wickwire EM, Klick B, Grace E, Smith MT. Naturalistic changes in insomnia symptoms and pain in temporomandibular joint disorder: a crosslagged panel analysis. Pain 2010;149:325–31. [22] Åkerstedt T, Fredlund P, Gillberg M, Jansson B. A prospective study of fatal occupational accidents—relationship to sleeping difficulties and occupational factors. J Sleep Res 2002;11:69–71. [23] Shekleton JA, Rogers NL, Rajaratnam SM. Searching for the daytime impairments of primary insomnia. Sleep Med Rev 2010;14:47–60. [24] Kottak CP. Primetime society: an anthropological analysis of television and culture, updated edition. Walnut Creek, CA: Left Coast Press; 2009. [25] Costa G. Shift work and occupational medicine: an overview. Occup Med 2003;53:83–8. [26] Suganuma N, Kikuchi T, Yanagi K, Yamamura S, Morishima H, Adachi H, et al. Using electronic media before sleep can curtail sleep time and result in selfperceived insufficient sleep. J Biol Rhythms 2007;5:204–14. [27] Rajaratnam SM, Arendt J. Health in a 24-h society. Lancet 2001;358:999–1005. [28] Manson JE, Skerrett PJ, Greenland P, VanItallie TB. The escalating pandemics of obesity and sedentary lifestyl—a call to action for clinicians. Arch Intern Med 2004;164:249–58. [29] Bin YS, Marshall NS, Glozier N. Secular trends in adult sleep duration: a systematic review. Sleep Med Rev 2012;16:223–30. [30] Ravan AR, Bengtsson C, Lissner L, Lapidus L, Björkelund C. Thirty-six-year secular trends in sleep duration and sleep satisfaction, and associations with mental stress and socioeconomic factors—results of the population study of women in Gothenburg, Sweden. J Sleep Res 2010;19:496–503. [31] Kronholm E, Partonen T, Laatikainen T, Peltonen M, Harma M, Hublin C, et al. Trends in self-reported sleep duration and insomnia-related symptoms in Finland from 1972 to 2005: a comparative review and re-analysis of Finnish population samples. J Sleep Res 2008;17:54–62. [32] Santos-Silva R, Bittencourt LR, Pires ML, de Mello MT, Taddei JA, Benedito-Silva AA, et al. Increasing trends of sleep complaints in the city of Sao Paulo, Brazil. Sleep Med 2010;11:520–4. [33] Salmon CT, Nichols JS. The next-birthday method of respondent selection. Public Opin Q 1983;47:270–6. [34] Pallesen S, Hetland J, Sivertsen B, Samdal O, Torsheim T, Nordhus IH. Time trends in sleep-onset difficulties among Norwegian adolescents: 1983–2005. Scand J Public Health 2008;36:889–95. [35] Simpson KRS, Meadows GN, Frances AJ, Patten SB. Is mental health in the Canadian population changing over time? Can J Psychiatry 2012;57:324–31.
179
[36] Härenstam A. Different development trends in working life and increasing occupational stress require new work environment strategies. Work 2005;24:261–77. [37] Sivertsen B, Øverland S, Pallesen S. Trends in timing of sleep in the general population of Norway: 1980–2000. Percept Mot Skills 2011;113:509–18. [38] Gellis LA, Lichstein KL. Sleep hygiene practices of good and poor sleepers in the United States: an Internet-based study. Behav Ther 2009;40:1–9. [39] Weaver E, Gradisar M, Dohnt H, Lovato B, Douglas P. The effect of presleep video-game playing on adolescent sleep. J Clin Sleep Med 2010;6:184–9. [40] Brunborg GS, Mentzoni RA, Molde H, Myrseth H, Skouveroe KJ, Bjorvatn B, et al. The relationship between media use in the bedroom, sleep habits and symptoms of insomnia. J Sleep Res 2011;20:569–75. [41] Van den Bulck J. Adolescent use of mobile phones for calling and for sending text messages after lights out: results from a prospective cohort study with a one-year follow-up. Sleep 2007;30:1220–3. [42] Higuchi S, Motohashi Y, Liu Y, Maeda A. Effects of playing a computer game using a bright display on presleep physiological variables, sleep latency, slow wave sleep and REM sleep. J Sleep Res 2005;14:267–73. [43] Carmelli D, Swan GE, Bliwise DL. Relationship of 30-year changes in obesity to sleep-disordered breathing in the Western Collaborative Group Study. Obes Res 2000;8:632–7. [44] Resta O, Barbaro MPF, Bonfitto P, Giliberti T, Depalo A, Pannacciulli N, et al. Low sleep quality and daytime sleepiness in obese patients without obstructive sleep apnoea syndrome. J Intern Med 2003;253:536–43. [45] Mykletun A, Knudsen AK, Mathiesen KS. Psychiatric disorders in Norway: a public health perspective [in Norwegian]. Oslo, Norway: Norwegian Institute of Public Health; 2009. [46] Bliwise DL, Ansari FP, Straight LB, Parker KP. Age changes in timing and 24-h distribution of self-reported sleep. Am J Geriatr Psychiatry 2005;13:1077–82. [47] Klerman EB, Davis JB, Duffy JF, Dijk DJ, Kronauer RE. Older people awaken more frequently but fall back asleep at the same rate as younger people. Sleep 2004;27:793–8. [48] Catala E, Reig E, Artes M, Aliaga L, Lopez JS, Segu JL. Prevalence of pain in the Spanish population: telephone survey in 5000 homes. Eur J Pain 2002;6:133–40. [49] Bixler EO, Vgontzas AN, Ten Have T, Tyson K, Kales A. Effects of age on sleep apnea in men I. Prevalence and severity. Am J Respir Crit Care Med 1998;157:144–8. [50] Omvik S, Pallesen S, Bjorvatn B, Sivertsen B, Havik OE, Nordhus IH. Patient characteristics and predictors of sleep medication use. Int Clin Psychopharmacol 2010;25:91–100. [51] Søgaard AJ, Selmer R, Bjertness E, Thelle D. The Oslo Health Study: the impact of self-selection in a large, population-based survey. Int J Equity Health 2004;3:3. [52] Torvik FA, Rognmo K, Tambs K. Alcohol use and mental distress as predictors of non-response in a general population health survey: the HUNT study. Soc Psychiatry Psychiatr Epidemiol 2012;47:805–16. [53] Morin CM, Bélanger L, LeBlanc M, Ivers H, Savard J, Espie CA, et al. The natural history of insomnia: a population-based 3-year longitudinal study. Arch Intern Med 2009;169:447–53. [54] Zhang J, Lam SP, Li SX, Yu MW, Li AM, Ma RC, et al. Long-term outcomes and predictors of chronic insomnia: a prospective study in Hong Kong Chinese adults. Sleep Med 2012;13:455–62. [55] Cohen J. Statistical power analysis for the behavioral sciences. 2nd ed. Hillsdale, NJ: Lawrence Erlbaum Associates Publishers; 1988. [56] Wade AG. The societal costs of insomnia. Neuropsychiatry Dis Treat 2011;7:1–18. [57] Bjorvatn B, Fiske E, Pallesen S. A self-help book is better than sleep hygiene advice for insomnia: a randomized controlled comparative study. Scand J Psychol 2011;52:580–5.
