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Psychological factors and insomnia among male civil servants in Japan
Sleep Medicine 8 (2007) 209–214 www.elsevier.com/locate/sleep
Original article
Psychological factors and insomnia among male civil servants in Japan Chiyoe Murata a
a,*
, Hiroshi Yatsuya b, Koji Tamakoshi b, Rei Otsuka b, Keiko Wada b, Hideaki Toyoshima b
Department of Community Health and Preventive Medicine, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu, Shizuoka 431-3192, Japan b Department of Public Health/Health Information Dynamics, Field of Social Life Science, Program in Health and Community Medicine, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan Received 9 March 2006; received in revised form 16 January 2007; accepted 22 January 2007 Available online 21 March 2007
Abstract Objective: This study aims at assessing the relative impact of psychological factors on insomnia among daytime workers. Background: Insomnia affects 5–45% of non-shift workers, making it a serious public health concern. Methods: The study population was 3435 male civil servants aged 35 years and over. A self-administered questionnaire survey was conducted in 2002. Annual health examination data compiled in the same year were also obtained. Insomnia was assessed in three domains: difficulty initiating sleep (DIS), difficulty maintaining sleep (DMS), and poor quality of sleep (PQS). Association of each factor with insomnia was examined by age-adjusted logistic regression models. Factors significantly associated with insomnia in ageadjusted analyses were entered in the stepwise logistic regression models to test the relative impact of each factor. Results: Prevalence of insomnia was 12.3% (DIS), 20.4% (DMS), and 32% (PQS). In stepwise logistic models, high perceived stress was associated with all types of insomnia with odds ratios (95% confidence interval) of 2.27 (1.58–3.26), 2.15 (1.57–2.95), and 2.96 (2.19–3.99), for DIS, DMS, and PQS, respectively. Poor psychological well-being or not having confidants was also associated with insomnia. Somatic conditions such as illnesses or history of hospitalization were related to DIS and DMS. Conclusions: Psychological factors were strongly associated with DIS and PQS after controlling for possible confounders. In dealing with insomnia, such factors must not be neglected. Ó 2007 Published by Elsevier B.V. Keywords: Insomnia; Middle age; Sleep complaints; Job stressors; Civil servants; Perceived stress
1. Introduction Insomnia is defined as inadequate or poor quality of sleep [1]. According to a review of 24 studies conducted in Japan, insomnia affects 5–45% of non-shift workers [2]. Insomnia often leads to absenteeism, lost productivity and accidents in the workplace. A recent study conducted with 4868 Japanese telecommunication workers *
Corresponding author. Tel.: +81 053 435 2333; fax: +81 053 435 2341. E-mail address: [email protected] (C. Murata). 1389-9457/$ - see front matter Ó 2007 Published by Elsevier B.V. doi:10.1016/j.sleep.2007.01.008
reported that poor sleepers were more likely than those who sleep well to take a sick leave, suffer from physical and mental problems, and have problems in occupational activities and personal relationships [3]. Causes of insomnia are complex and may result from a combination of various factors, such as physical or mental problems. Physical factors include side effects of medication, arthritis, heart disease, asthma, sleep apnea, and narcolepsy. Lifestyle-related factors such as caffeine intake or alcohol consumption may also cause insomnia [1]. Insomnia is also associated with various types of mental illnesses such as depression. A recent
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study on people having attempted suicide who were admitted to an emergency hospital in Japan indicated that about 30% of those people had depression, according to the diagnostic criteria of the International Classification of Diseases, 10th revision (ICD-10) [4]. Another study in the Japanese workplace reported as much as 70% of suicide cases had depression [5]. In addition, a higher incidence of cardiovascular disease among people with sleep complaints was reported [6]. Stress may cause changes in autonomic indices such as heart rate variability, temperature, and metabolic rate that lead to hyperarousal during the night. Psychological stress is also one of the major causes of insomnia among community residents and workers [7]. Given the fact that insomnia is related to various health problems, this is a serious public health concern today, and examining factors associated with insomnia merits further attention. The aim of this study was to assess the relative impact of job stressors, somatic conditions, and psychological factors such as perceived stress, psychological well-being, and availability of confidants on insomnia among male civil servants in Japan. 2. Methods 2.1. Subjects This study was a part of a cohort study on cardiovascular disease conducted with civil servants in Japan. Self-administered questionnaires on job stressors, lifestyle-related items, medical conditions, psychological factors, and absence or presence of insomnia were distributed to 10 759 Aichi prefecture government employees prior to annual health examination in 2002. Questionnaires were returned by 7991 employees, with a response rate of 74.3%, and written informed consent to use personal information for analyses was obtained from 6651 respondents (5179 men and 1472 women). In this study, we limited the analyses to male white-collar workers (N = 3435) aged 35–66 years. Shift workers (n = 43) were excluded to minimize the possible effect of circadian rhythm disruption on insomnia, yielding 3392 subjects for the analysis. The study protocol was approved by the Ethics Committee of Nagoya University Graduate School of Medicine, Nagoya, Japan. 2.2. Variables Insomnia was assessed in three domains by inquiring about the following symptoms: having difficulty falling asleep after being in bed (DIS: difficulty initiating sleep), waking up often in the middle of the night (DMS: difficulty maintaining sleep), and not feeling refreshed when waking up in the morning (PQS: poor quality of sleep). The response choices were dichotomous (yes or no).
To assess job stressors, we used a questionnaire with items related to quantitative workload (4 items), cognitive demand (3 items), job control (3 items), human relations in the workplace (3 items), physical environment (1 item), underutilization of skills (1 item), and job satisfaction (2 items). This questionnaire is a part of a simplified version of a job stress questionnaire developed by a study group of the Ministry of Labour, Health and Welfare in Japan, based on the Job Content Questionnaire (JCQ) developed by Karasek [8] and the Japanese version of the Generic Job Stress Questionnaire (GJSQ) developed by National Institute for Occupational Safety and Health (NIOSH) in the United States [9]. Both the JCQ and GJSQ are comprehensive instruments based on a job stress model and are widely used in occupational health research. The simplified version of the job stress questionnaire demonstrated modest internal reliability in job stressor items (Cronbach’s alpha, 0.64–0.79) and validity [10]. Overtime work hours were also assessed and used in the analysis since long work hours are often pointed to as a cause of stress in occupational settings [11]. In the analysis, those who worked more than 8 h per day were considered to have worked overtime. Somatic conditions such as the history of hospitalization in the past 5 years or current illnesses under treatment were assessed by self-report. Such illnesses include cancer, heart disease, stroke, allergic rhinitis, diabetes, hyperlipidemia, hypertension, hyperuricemia, and others. Psychological factors were assessed by asking questions about perceived stress in general, purpose in life (ikigai) defined as one aspect of psychological well-being to judge one’s life as good and meaningful and to feel that it is worth living [12], and availability of confidants when distressed. Perceived stress was assessed by asking, ‘‘Do you have much stress in your daily life?’’ Response choices included ‘‘very much,’’ ‘‘much,’’ ‘‘ordinary,’’ and ‘‘little.’’ For psychological well-being, we asked if respondents considered their life meaningful and worth living (ikigai). Four response choices were ‘‘yes, a lot,’’ ‘‘yes,’’ ‘‘so so,’’ and ‘‘not sure.’’ Availability of confidants was assessed by asking if respondents had someone to talk to when distressed. The response choices were ‘‘yes,’’ ‘‘no,’’ and ‘‘seldom feel distressed.’’ As controlling factors, we used age in years, blood pressure, body mass index (BMI), caffeine intake (measured as cups of coffee/week), regular exercise (at least once a month for more than 60 min), alcohol consumption, and smoking. Data on blood pressure and BMI were obtained from the annual health examination in the same year. Hours of sleep per day was also inquired about since studies to date have demonstrated that short sleep was associated with health outcomes such as heart disease [13].
C. Murata et al. / Sleep Medicine 8 (2007) 209–214
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2.3. Statistical analysis
Table 2 Age-adjusted odds ratios of somatic conditions for insomnia
Associations of surveyed items with each type of insomnia were examined by age-adjusted logistic regression models. After age-adjusted analyses, only factors significantly associated with insomnia were entered in the stepwise logistic regression models to test the relative impact of each factor on insomnia. The limits for entry and removal of variables were 0.10 and 0.15 (default values), respectively. All analyses were carried out using the SPSS statistical package for Windows version 12.0.
Factors (reference)
Category or range
Hospitalization Cancer (no) Heart disease (no)
Yes Yes
3.86** 2.52*
Current illnesses Diabetes (no) Hyperuricemia (no) Hypertension (no) Hyperlipidemia (no) Others (no)
Yes Yes Yes Yes Yes
1.53** 1.51** 1.44** 1.23 1.39**
3. Results Overall, 54.6% of respondents reported insomnia. Among these, 85.5% reported only one symptom of insomnia, while 11.2% reported two symptoms, and other 3.6% reported all the three symptoms. Spearman correlation coefficients were 0.049 (p < 0.001) for DIS and DMS, 0.013 (not significant) for DIS and PQS, and 0.049 (p < 0.001) for DMS and PQS, respectively, demonstrating weak correlations among each type of insomnia. Prevalence by type of insomnia was 12.3%, 20.4%, and 32% for DIS, DMS, and PQS, respectively (Table 1). In crude logistic models, older age was significantly associated with DMS and younger age with PQS.
Table 1 Covariates in study population (n = 3392)
DIS
DMS
1.31*
PQS
Odds ratios were calculated adjusting for age in years using logistic regression models. p < 0.10. * p < 0.05. ** p < 0.01.
Table 3 Age-adjusted odds ratios of job stressors for insomnia Job stressors (reference)
Category or range
DIS
DMS
PQS
Demand (low) Control (high) Human relations (good) Job satisfaction (yes) Skill utilization (yes) Physical environment (good) Overtime working hours
High Low Poor
1.31* 1.56**
1.20 1.39*** 1.48**
1.44*** 1.31** 2.01***
1.37**
1.53***
1.71*** 1.36*** 1.42***
No No Poor
1.21***
0–7 h/day
Variables
N (%) or mean (SD, range)
Age in years 35–39 40–44 45–49 50–54 55–59 60+
48.1 (6.9, 35–66) 490 (14.4) 591 (17.4) 689 (20.3) 1027 (30.3) 485 (14.3) 110 (3.2)
Job status Managers (yes)
799 (23.6)
Table 4 Age-adjusted odds ratios of psychological factors for insomnia
1194 (35.4) 21.3 (27.0, 0–201) 11.3 ( 8.0, 0–28) 1948 (57.4)
Psychological factors (reference)
Category or range
DIS
DMS
PQS
Ikigai (purpose in life) (yes)
Not sure So–so A lot
2.76*** 1.34*
2.46*** 1.50***
3.37*** 1.51*** 0.64
Perceived stress (ordinary)
Very much Much Little
2.54*** 1.46**
2.65*** 1.48***
4.09*** 2.20*** 0.49**
Availability of confidants when distressed (yes)
No Seldom feel distressed
1.27* 0.73*
1.99***
1.52*** 0.61***
Life style-related factors Smoking (yes) Alcohol intake (ethanol (g)/week) Caffeine intake (cups of coffee/week) Regular exercise (60+mins and at least once/month) Hours of sleep/night
6.58 (0.85, 2.5–10.0)
Biomedical measures BMI SBP DBP
23.3 (2.8, 15.1–37.8) 127.8 (15.0, 84.0–191.0) 79.4 (11.2, 38.0–130.0)
Insomnia DIS DMS PQS
1853 (54.6) 416 (12.3) 693 (20.4) 1086 (32.0)
DIS, difficulty initiating sleep; DMS, difficulty maintaining sleep; PQS, poor quality of sleep; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure.
Odds ratios were calculated adjusting for age in years using logistic regression models. p < 0.10. * p < 0.05. ** p < 0.01. *** p < 0.001.
Odds ratios were calculated adjusting for age in years using logistic regression models. p < 0.10. * p < 0.05. ** p < 0.01. *** p < 0.001.
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Tables 2, 3 and 4 show age-adjusted odds ratios of each variable for insomnia. History of hospitalization in the past 5 years due to cancer or heart disease was associated with DMS. As for current illnesses under treatment, hypertension was associated with DIS. Diabetes, hyperuricemia, hypertension, hyperlipidemia, and others were associated with DMS (Table 2). For job stressors, high demand (high quantitative workload and cognitive demand) was associated with DMS and PQS. Low job control, poor workplace human relations, and low job satisfaction were associated with all types of insomnia. Underutilization of
skills, poor physical environment in the workplace, and hours worked overtime were associated with PQS only (Table 3). As for psychological factors, not considering their life meaningful or worth living (ikigai), higher perceived stress, and not having someone to talk to when distressed were associated with all types of insomnia. Those who responded that they seldom felt distressed had lower odds for DIS and PQS (Table 4). Table 5 shows the results of stepwise multivariate logistic models by each type of insomnia. Hospitalization in the past 5 years due to cancer or heart disease
Table 5 Odds ratios of factors independently associated with insomnia in logistic models with stepwise method
DIS
Factors (reference)
Category or range
Odds ratio
Ikigai (purpose in life) (yes)
So–so Not sure Very much Much Seldom feel distressed 35–66 Yes Yes Yes So–so Not sure Very much Much No Yes 35–66 A lot So–so Not sure Very much Much Little Seldom feel distressed Yes 0–7 h/day
1.31 2.08*** 2.08*** 1.37* 0.68* 1.04*** 3.31* 2.76* 1.44 1.51** 1.78** 2.30*** 1.42** 1.55*** 1.24* 0.98* 0.59 1.57*** 2.78*** 2.91*** 1.90*** 0.58* 0.74** 1.41** 1.11*
Perceived stress (ordinary)
DMS
Availability of confidants when distressed (no) Age in years Hospitalization due to cancer (no) Hospitalization due to heart disease (no) Hyperuricemia (no) Ikigai (purpose in life) (yes) Perceived stress (ordinary)
PQS
Availability of confidants when distressed (yes) Job dissatisfaction (no) Age in years Ikigai (purpose in life) (yes)
Perceived stress (ordinary)
Availability of confidants when distressed (yes) Poor workplace human relations (no) Mean overtime working hours
Controlled variables were age, BMI, blood pressure, smoking, drinking, caffeine intake, and exercise habit. p < 0.10. * p < 0.05. ** p < 0.01. *** p < 0.001.
Table 6 Proportion of those who reported job stressors and mean overtime working hours by age group (%) Job stressors
High demand Low control Poor workplace human relations Job dissatisfaction Skill underutilization Poor physical environment Overtime working Mean overtime working hours per day
Age group 35–39
40–44
45–49
50–54
55–59
60+
p for trend
29.5 42.7 15.8 28.2 32.2 36.4 58.8
30.0 45.9 14.3 28.5 29.4 39.7 60.1
26.1 36.2 14.0 27.4 28.3 35.4 47.0
26.2 34.8 14.0 25.0 32.9 26.4 36.9
19.1 25.6 9.2 17.0 26.7 18.8 24.5
4.8 39.6 4.8 22.4 41.7 13.9 3.6
<0.001 <0.001 <0.01 <0.001 n.s. <0.001 <0.001
2.08
1.90
1.70
1.53
1.27
1.50
<0.001
C. Murata et al. / Sleep Medicine 8 (2007) 209–214
was associated with DMS only. Those with diagnosed hyperuricemia had higher odds for DMS. In psychological factors, higher perceived stress and not considering their life meaningful or worth living (ikigai) were associated with all types of insomnia. Not having confidants was associated with DMS, and seldom feeling distressed was associated with lower odds for DIS and PQS. In job stressors, job dissatisfaction was associated with DMS. Poor human relations in the workplace and longer hours worked overtime were associated with PQS. In addition, workers in younger age groups reported more job stressors and worked extra hours compared to their older counterparts (Table 6). 4. Discussion Psychological factors, such as higher perceived stress or not considering their life meaningful or worth living (ikigai), were associated with all types of insomnia even after controlling for possible confounders such as blood pressure, BMI, medical treatment, and lifestyle-related factors. Recent studies conducted in the Japanese workplace demonstrated a strong association between psychological job stress and insomnia [7,14]. Another study in Finland reported the effects of stress in daily life, such as family problems, on insomnia in a community population [15]. Although the cross-sectional nature of our study makes definite conclusions on causation difficult, the association of psychological factors with insomnia seems to be strong. One explanation might be stress. A study in Sweden indicated that although working under high demands was a risk factor for insomnia, not high demands per se but the effect on unwinding after work causes sleep problems. The authors suggested that the inability to free oneself of thoughts of work during leisure time might explain such an association [11]. Although we did not limit the stress to being workrelated when asking the question, observed association of job stressors with insomnia seemed to be mediated by perceived stress since the association of job stressors with insomnia was attenuated substantially when perceived stress was entered into the model (data not shown). To confirm the association, we conducted additional multiple regression analyses with perceived stress as a dependent variable. All the job stressors except for underutilization of skills were significantly associated with higher perceived stress. High demand, poor human relations in the workplace, low job control, low job satisfaction, and poor physical environment in the workplace predicted 10.9%, 2.3%, 1.8%, 0.5%, and 0.1% of variances in perceived stress, respectively. To interpret the association between perceived stress and insomnia, we may need to consider personal traits as well, since not every person responds to a stress in
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the same way. In fact, those who answered that they seldom felt distressed had lower odds for PQS compared to those who felt distressed but had a confidant. This may indicate that in occupational settings merely eliminating job stressors may not be sufficient, but psychological interventions such as teaching human relation skills or stress management techniques may also be required. A review reported that a psychotherapeutic approach improved sleep quality of patients in various studies [6]. In the current study, a higher rate of PQS was observed among younger workers. The explanation might be longer working hours compared to their older counterparts. As shown in Table 6, those in the 35- to 44-year-old age group worked longer hours per day and reported more job stressors compared to other age groups. Additional analyses indicated that those who worked overtime slept significantly (p < 0.001) fewer hours (mean: 6.37 h) than those who did not do so (mean: 6.74 h). There is a report indicating that overtime work is a risk factor for acute myocardial infarction [16] as well as for depression [17]. We need to further investigate the association between long work hours and health problems more seriously. Poor human relations in the workplace were also associated with PQS. A study conducted in the Japanese workplace suggested that in Asian cultures where harmony in human relations is valued, human relations in the workplace may have a strong impact on job-related stress [7]. Another study in Sweden reported that those with more social support had lower risk of insomnia, indicating that social support had an effect on the reduction of sleep problems [11]. Somatic conditions such as past hospitalization or treated hyperuricemia were associated with DMS among our population. In a study in Finland, those hospitalized during the previous 5 years reported more insomnia [15]. Some medication stimulates patients and often causes early morning awakening or arousal during the night [6]. In age-adjusted models, receiving treatment for hypertension was associated with DIS and DMS. Current diabetes, hyperuricemia, and hyperlipidemia were associated with DMS (Table 2). It is possible that medication constitutes a cause of insomnia, especially among those reporting DIS and DMS. Sleep apnea is often pointed to as a cause of insomnia [18]. In this study, we did not ask if respondents had excessive daytime sleepiness or fatigue, symptoms of sleep apnea that are well-known risk factors for insomnia, nor did we ask if respondents snore during the night. However, the effect of sleep apnea may be relatively small in our population since the degree of obesity as measured by BMI, a major risk factor of sleep apnea, was not associated with insomnia in the preliminary analyses. Lastly, we should touch upon some limitations in our study. Depression was not assessed among our
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population. Although considering life meaningful and worth living (ikigai) was associated with insomnia, we could not rule out the possibility that those who reported insomnia already suffered from depression. A study reported a depression rate of as much as 38.6% among the working population in Japan [19]. Since studies have reported a higher incidence of depression among insomniacs [6,17], we need to consider mental health problems more seriously in dealing with insomnia. For that, sleep complaints may serve as a useful indicator to identify those under stress and at risk of developing mental problems such as depression. Another limitation is that insomnia was assessed based on self-report only. Although a study concluded that self-reported insomnia was independent of poor sleep as measured by electroencephalography and that sleep complaints were not always concordant with such objective measures [20], the association of sleep complaints with objective sleep quality needs to be investigated in detail in future studies. In addition, depression and anxiety need to be measured for effective interventions. Finally, insomnia was assessed based on three questions with binary responses (yes or no). This may have contributed to the higher prevalence of insomnia among our study population. To identify cases of insomnia, we need to use validated instruments such as the Japanese version of the Pittsburgh Sleep Quality Index (PSQI-J) [21] or the diagnostic criteria of the ICD-10 [4] with information about the time and duration of symptoms. 5. Conclusions Due to the above-mentioned limitations, reaching a definite conclusion about the relationship between psychological factors and insomnia might be difficult. Nonetheless, this study indicated that psychological factors, such as not considering life meaningful or worth living (ikigai), not having someone to talk to when distressed, and higher perceived stress, were related to all types of insomnia, even after adjusting for possible confounders. In addition, poor human relations in the workplace and longer work hours were related to PQS in which younger age groups were disproportionately at risk in our population. Our results suggest the importance of considering psychological factors in addition to somatic conditions in dealing with insomnia among working populations. Acknowledgements This study was supported in part by grants from the Ministry of Education, Culture, Sports, Science and Technology and the Japan Atherosclerosis Prevention Fund (JAPF).
References [1] National center on sleep disorders research and office of prevention education, and control. Insomnia: assessment and management in primary care. National Institute of Health Publication No.98-4088: Sept 1998. [2] Doi Y. An epidemiologic review on occupational sleep research among Japanese workers. Ind Health 2005;43:3–10. [3] Doi Y, Minowa M, Tango T. Impact and correlates of poor sleep quality in Japanese white-collar employees. Sleep 2003;26:467–71. [4] Ichimura A, Matsumoto H, Kimura T, Okuyama T, Watanabe T, Nakagawa Y, et al. Changes in mental disorder distribution among suicide attempters in mid-west area of Kanagawa. Psychiatry Clin Neurosci 2005;59:113–8. [5] Arai M. Prospective study and preventive measures of suicide among workers: in case of depression. Rinsho Seishin Byori 1991;12:119–31. in Japanese. [6] Roth T, Drake C. Evolution of insomnia: current status and future direction. Sleep Med 2004;5(Suppl. 1):S23–30. [7] Nakata A, Haratani T, Takahashi M, Kawakami N, Arito H, Kobayashi F, et al. Job stress, social support, and prevalence of insomnia in a population of Japanese daytime workers. Soc Sci Med 2004;59:1719–30. [8] Karasek RA, Theorell T. Healthy Work: Stress, Productivity, and the Reconstruction of Working Life. New York: Basic Books; 1990. [9] Kawakami N, Fujigaki Y. Reliability and validity of the Japanese version of Job Content Questionnaire: replication and extension in computer company employees. Ind Health 1996;34:295–306. [10] Kato M. Report on work-related stress and its effect on health. Tokyo:MinistryofHealth, Labour, andWelfare;2000(inJapanese). [11] Akerstedt T, Knutsson A, Westerholm P, Theorell T, Alfredsson L, Kecklund G. Sleep disturbances, work stress and work hours: a cross-sectional study. J Psychosom Res 2002;53:741–8. [12] Yamamoto-Mitani N, Wallhagen MI. Pursuit of psychological wellbeing (ikigai) and the evolution of self-understanding in the context of caregiving in Japan. Cult Med Psychiatry 2002;26:399–417. [13] Ayas NT, White DP, Manson JE, Stampfer MJ, Speizer FE, Malhotra A, et al. A prospective study of sleep duration and coronary heart disease in women. Arch Intern Med 2003;163:205–9. [14] Ota A, Masue T, Yasuda N, Tsutsumi A, Mino Y, Ohara H. Association between psychosocial job characteristics and insomnia: an investigation using two relevant job stress models—the demand-control-support (DCS) model and the effort-reward imbalance (ERI) model. Sleep Med 2005;6:353–8. [15] Martikainen K, Partinen M, Hasan J, Laippala P, Urponen H, Vuori I. The impact of somatic health problems on insomnia in middle age. Sleep Med 2003;4:201–6. [16] Sokejima S, Kagamimori S. Working hours as a risk factor for acute myocardial infarction in Japan: case-control study. BMJ 1998;317:775–80. [17] Lustberg L, Reynolds CF. Depression and insomnia: questions of cause and effect. Sleep Med Rev 2000;4:253–62. [18] Simon S, Karen S, Wendy H, James D. Frequency of insomnia report in patients with obstructive sleep apnoea hypopnea syndrome (OSAHS). Sleep Med 2004;5:449–56. [19] Nakata A, Ikeda T, Takahashi M, Haratani T, Fujioka Y, Fukui S, et al. Sleep-related risk of occupational injuries in Japanese small and medium-scale enterprises. Ind Health 2005;43:89–97. [20] Rosa RR, Bonnet MH. Reported chronic insomnia is independent of poor sleep as measured by electroencephalography. Psychosom Med 2000;62:474–82. [21] Doi Y, Minowa M, Uchiyama M, Okawa M, Kim K, Shibui K, et al. Psychometric assessment of subjective sleep quality using the Japanese version of the Pittsburgh Sleep Quality Index (PSQI-J) in psychiatric disordered and control subjects. Psychiatry Res 2000;97:165–72.
Original article
Psychological factors and insomnia among male civil servants in Japan Chiyoe Murata a
a,*
, Hiroshi Yatsuya b, Koji Tamakoshi b, Rei Otsuka b, Keiko Wada b, Hideaki Toyoshima b
Department of Community Health and Preventive Medicine, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu, Shizuoka 431-3192, Japan b Department of Public Health/Health Information Dynamics, Field of Social Life Science, Program in Health and Community Medicine, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan Received 9 March 2006; received in revised form 16 January 2007; accepted 22 January 2007 Available online 21 March 2007
Abstract Objective: This study aims at assessing the relative impact of psychological factors on insomnia among daytime workers. Background: Insomnia affects 5–45% of non-shift workers, making it a serious public health concern. Methods: The study population was 3435 male civil servants aged 35 years and over. A self-administered questionnaire survey was conducted in 2002. Annual health examination data compiled in the same year were also obtained. Insomnia was assessed in three domains: difficulty initiating sleep (DIS), difficulty maintaining sleep (DMS), and poor quality of sleep (PQS). Association of each factor with insomnia was examined by age-adjusted logistic regression models. Factors significantly associated with insomnia in ageadjusted analyses were entered in the stepwise logistic regression models to test the relative impact of each factor. Results: Prevalence of insomnia was 12.3% (DIS), 20.4% (DMS), and 32% (PQS). In stepwise logistic models, high perceived stress was associated with all types of insomnia with odds ratios (95% confidence interval) of 2.27 (1.58–3.26), 2.15 (1.57–2.95), and 2.96 (2.19–3.99), for DIS, DMS, and PQS, respectively. Poor psychological well-being or not having confidants was also associated with insomnia. Somatic conditions such as illnesses or history of hospitalization were related to DIS and DMS. Conclusions: Psychological factors were strongly associated with DIS and PQS after controlling for possible confounders. In dealing with insomnia, such factors must not be neglected. Ó 2007 Published by Elsevier B.V. Keywords: Insomnia; Middle age; Sleep complaints; Job stressors; Civil servants; Perceived stress
1. Introduction Insomnia is defined as inadequate or poor quality of sleep [1]. According to a review of 24 studies conducted in Japan, insomnia affects 5–45% of non-shift workers [2]. Insomnia often leads to absenteeism, lost productivity and accidents in the workplace. A recent study conducted with 4868 Japanese telecommunication workers *
Corresponding author. Tel.: +81 053 435 2333; fax: +81 053 435 2341. E-mail address: [email protected] (C. Murata). 1389-9457/$ - see front matter Ó 2007 Published by Elsevier B.V. doi:10.1016/j.sleep.2007.01.008
reported that poor sleepers were more likely than those who sleep well to take a sick leave, suffer from physical and mental problems, and have problems in occupational activities and personal relationships [3]. Causes of insomnia are complex and may result from a combination of various factors, such as physical or mental problems. Physical factors include side effects of medication, arthritis, heart disease, asthma, sleep apnea, and narcolepsy. Lifestyle-related factors such as caffeine intake or alcohol consumption may also cause insomnia [1]. Insomnia is also associated with various types of mental illnesses such as depression. A recent
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study on people having attempted suicide who were admitted to an emergency hospital in Japan indicated that about 30% of those people had depression, according to the diagnostic criteria of the International Classification of Diseases, 10th revision (ICD-10) [4]. Another study in the Japanese workplace reported as much as 70% of suicide cases had depression [5]. In addition, a higher incidence of cardiovascular disease among people with sleep complaints was reported [6]. Stress may cause changes in autonomic indices such as heart rate variability, temperature, and metabolic rate that lead to hyperarousal during the night. Psychological stress is also one of the major causes of insomnia among community residents and workers [7]. Given the fact that insomnia is related to various health problems, this is a serious public health concern today, and examining factors associated with insomnia merits further attention. The aim of this study was to assess the relative impact of job stressors, somatic conditions, and psychological factors such as perceived stress, psychological well-being, and availability of confidants on insomnia among male civil servants in Japan. 2. Methods 2.1. Subjects This study was a part of a cohort study on cardiovascular disease conducted with civil servants in Japan. Self-administered questionnaires on job stressors, lifestyle-related items, medical conditions, psychological factors, and absence or presence of insomnia were distributed to 10 759 Aichi prefecture government employees prior to annual health examination in 2002. Questionnaires were returned by 7991 employees, with a response rate of 74.3%, and written informed consent to use personal information for analyses was obtained from 6651 respondents (5179 men and 1472 women). In this study, we limited the analyses to male white-collar workers (N = 3435) aged 35–66 years. Shift workers (n = 43) were excluded to minimize the possible effect of circadian rhythm disruption on insomnia, yielding 3392 subjects for the analysis. The study protocol was approved by the Ethics Committee of Nagoya University Graduate School of Medicine, Nagoya, Japan. 2.2. Variables Insomnia was assessed in three domains by inquiring about the following symptoms: having difficulty falling asleep after being in bed (DIS: difficulty initiating sleep), waking up often in the middle of the night (DMS: difficulty maintaining sleep), and not feeling refreshed when waking up in the morning (PQS: poor quality of sleep). The response choices were dichotomous (yes or no).
To assess job stressors, we used a questionnaire with items related to quantitative workload (4 items), cognitive demand (3 items), job control (3 items), human relations in the workplace (3 items), physical environment (1 item), underutilization of skills (1 item), and job satisfaction (2 items). This questionnaire is a part of a simplified version of a job stress questionnaire developed by a study group of the Ministry of Labour, Health and Welfare in Japan, based on the Job Content Questionnaire (JCQ) developed by Karasek [8] and the Japanese version of the Generic Job Stress Questionnaire (GJSQ) developed by National Institute for Occupational Safety and Health (NIOSH) in the United States [9]. Both the JCQ and GJSQ are comprehensive instruments based on a job stress model and are widely used in occupational health research. The simplified version of the job stress questionnaire demonstrated modest internal reliability in job stressor items (Cronbach’s alpha, 0.64–0.79) and validity [10]. Overtime work hours were also assessed and used in the analysis since long work hours are often pointed to as a cause of stress in occupational settings [11]. In the analysis, those who worked more than 8 h per day were considered to have worked overtime. Somatic conditions such as the history of hospitalization in the past 5 years or current illnesses under treatment were assessed by self-report. Such illnesses include cancer, heart disease, stroke, allergic rhinitis, diabetes, hyperlipidemia, hypertension, hyperuricemia, and others. Psychological factors were assessed by asking questions about perceived stress in general, purpose in life (ikigai) defined as one aspect of psychological well-being to judge one’s life as good and meaningful and to feel that it is worth living [12], and availability of confidants when distressed. Perceived stress was assessed by asking, ‘‘Do you have much stress in your daily life?’’ Response choices included ‘‘very much,’’ ‘‘much,’’ ‘‘ordinary,’’ and ‘‘little.’’ For psychological well-being, we asked if respondents considered their life meaningful and worth living (ikigai). Four response choices were ‘‘yes, a lot,’’ ‘‘yes,’’ ‘‘so so,’’ and ‘‘not sure.’’ Availability of confidants was assessed by asking if respondents had someone to talk to when distressed. The response choices were ‘‘yes,’’ ‘‘no,’’ and ‘‘seldom feel distressed.’’ As controlling factors, we used age in years, blood pressure, body mass index (BMI), caffeine intake (measured as cups of coffee/week), regular exercise (at least once a month for more than 60 min), alcohol consumption, and smoking. Data on blood pressure and BMI were obtained from the annual health examination in the same year. Hours of sleep per day was also inquired about since studies to date have demonstrated that short sleep was associated with health outcomes such as heart disease [13].
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2.3. Statistical analysis
Table 2 Age-adjusted odds ratios of somatic conditions for insomnia
Associations of surveyed items with each type of insomnia were examined by age-adjusted logistic regression models. After age-adjusted analyses, only factors significantly associated with insomnia were entered in the stepwise logistic regression models to test the relative impact of each factor on insomnia. The limits for entry and removal of variables were 0.10 and 0.15 (default values), respectively. All analyses were carried out using the SPSS statistical package for Windows version 12.0.
Factors (reference)
Category or range
Hospitalization Cancer (no) Heart disease (no)
Yes Yes
3.86** 2.52*
Current illnesses Diabetes (no) Hyperuricemia (no) Hypertension (no) Hyperlipidemia (no) Others (no)
Yes Yes Yes Yes Yes
1.53** 1.51** 1.44** 1.23 1.39**
3. Results Overall, 54.6% of respondents reported insomnia. Among these, 85.5% reported only one symptom of insomnia, while 11.2% reported two symptoms, and other 3.6% reported all the three symptoms. Spearman correlation coefficients were 0.049 (p < 0.001) for DIS and DMS, 0.013 (not significant) for DIS and PQS, and 0.049 (p < 0.001) for DMS and PQS, respectively, demonstrating weak correlations among each type of insomnia. Prevalence by type of insomnia was 12.3%, 20.4%, and 32% for DIS, DMS, and PQS, respectively (Table 1). In crude logistic models, older age was significantly associated with DMS and younger age with PQS.
Table 1 Covariates in study population (n = 3392)
DIS
DMS
1.31*
PQS
Odds ratios were calculated adjusting for age in years using logistic regression models. p < 0.10. * p < 0.05. ** p < 0.01.
Table 3 Age-adjusted odds ratios of job stressors for insomnia Job stressors (reference)
Category or range
DIS
DMS
PQS
Demand (low) Control (high) Human relations (good) Job satisfaction (yes) Skill utilization (yes) Physical environment (good) Overtime working hours
High Low Poor
1.31* 1.56**
1.20 1.39*** 1.48**
1.44*** 1.31** 2.01***
1.37**
1.53***
1.71*** 1.36*** 1.42***
No No Poor
1.21***
0–7 h/day
Variables
N (%) or mean (SD, range)
Age in years 35–39 40–44 45–49 50–54 55–59 60+
48.1 (6.9, 35–66) 490 (14.4) 591 (17.4) 689 (20.3) 1027 (30.3) 485 (14.3) 110 (3.2)
Job status Managers (yes)
799 (23.6)
Table 4 Age-adjusted odds ratios of psychological factors for insomnia
1194 (35.4) 21.3 (27.0, 0–201) 11.3 ( 8.0, 0–28) 1948 (57.4)
Psychological factors (reference)
Category or range
DIS
DMS
PQS
Ikigai (purpose in life) (yes)
Not sure So–so A lot
2.76*** 1.34*
2.46*** 1.50***
3.37*** 1.51*** 0.64
Perceived stress (ordinary)
Very much Much Little
2.54*** 1.46**
2.65*** 1.48***
4.09*** 2.20*** 0.49**
Availability of confidants when distressed (yes)
No Seldom feel distressed
1.27* 0.73*
1.99***
1.52*** 0.61***
Life style-related factors Smoking (yes) Alcohol intake (ethanol (g)/week) Caffeine intake (cups of coffee/week) Regular exercise (60+mins and at least once/month) Hours of sleep/night
6.58 (0.85, 2.5–10.0)
Biomedical measures BMI SBP DBP
23.3 (2.8, 15.1–37.8) 127.8 (15.0, 84.0–191.0) 79.4 (11.2, 38.0–130.0)
Insomnia DIS DMS PQS
1853 (54.6) 416 (12.3) 693 (20.4) 1086 (32.0)
DIS, difficulty initiating sleep; DMS, difficulty maintaining sleep; PQS, poor quality of sleep; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure.
Odds ratios were calculated adjusting for age in years using logistic regression models. p < 0.10. * p < 0.05. ** p < 0.01. *** p < 0.001.
Odds ratios were calculated adjusting for age in years using logistic regression models. p < 0.10. * p < 0.05. ** p < 0.01. *** p < 0.001.
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Tables 2, 3 and 4 show age-adjusted odds ratios of each variable for insomnia. History of hospitalization in the past 5 years due to cancer or heart disease was associated with DMS. As for current illnesses under treatment, hypertension was associated with DIS. Diabetes, hyperuricemia, hypertension, hyperlipidemia, and others were associated with DMS (Table 2). For job stressors, high demand (high quantitative workload and cognitive demand) was associated with DMS and PQS. Low job control, poor workplace human relations, and low job satisfaction were associated with all types of insomnia. Underutilization of
skills, poor physical environment in the workplace, and hours worked overtime were associated with PQS only (Table 3). As for psychological factors, not considering their life meaningful or worth living (ikigai), higher perceived stress, and not having someone to talk to when distressed were associated with all types of insomnia. Those who responded that they seldom felt distressed had lower odds for DIS and PQS (Table 4). Table 5 shows the results of stepwise multivariate logistic models by each type of insomnia. Hospitalization in the past 5 years due to cancer or heart disease
Table 5 Odds ratios of factors independently associated with insomnia in logistic models with stepwise method
DIS
Factors (reference)
Category or range
Odds ratio
Ikigai (purpose in life) (yes)
So–so Not sure Very much Much Seldom feel distressed 35–66 Yes Yes Yes So–so Not sure Very much Much No Yes 35–66 A lot So–so Not sure Very much Much Little Seldom feel distressed Yes 0–7 h/day
1.31 2.08*** 2.08*** 1.37* 0.68* 1.04*** 3.31* 2.76* 1.44 1.51** 1.78** 2.30*** 1.42** 1.55*** 1.24* 0.98* 0.59 1.57*** 2.78*** 2.91*** 1.90*** 0.58* 0.74** 1.41** 1.11*
Perceived stress (ordinary)
DMS
Availability of confidants when distressed (no) Age in years Hospitalization due to cancer (no) Hospitalization due to heart disease (no) Hyperuricemia (no) Ikigai (purpose in life) (yes) Perceived stress (ordinary)
PQS
Availability of confidants when distressed (yes) Job dissatisfaction (no) Age in years Ikigai (purpose in life) (yes)
Perceived stress (ordinary)
Availability of confidants when distressed (yes) Poor workplace human relations (no) Mean overtime working hours
Controlled variables were age, BMI, blood pressure, smoking, drinking, caffeine intake, and exercise habit. p < 0.10. * p < 0.05. ** p < 0.01. *** p < 0.001.
Table 6 Proportion of those who reported job stressors and mean overtime working hours by age group (%) Job stressors
High demand Low control Poor workplace human relations Job dissatisfaction Skill underutilization Poor physical environment Overtime working Mean overtime working hours per day
Age group 35–39
40–44
45–49
50–54
55–59
60+
p for trend
29.5 42.7 15.8 28.2 32.2 36.4 58.8
30.0 45.9 14.3 28.5 29.4 39.7 60.1
26.1 36.2 14.0 27.4 28.3 35.4 47.0
26.2 34.8 14.0 25.0 32.9 26.4 36.9
19.1 25.6 9.2 17.0 26.7 18.8 24.5
4.8 39.6 4.8 22.4 41.7 13.9 3.6
<0.001 <0.001 <0.01 <0.001 n.s. <0.001 <0.001
2.08
1.90
1.70
1.53
1.27
1.50
<0.001
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was associated with DMS only. Those with diagnosed hyperuricemia had higher odds for DMS. In psychological factors, higher perceived stress and not considering their life meaningful or worth living (ikigai) were associated with all types of insomnia. Not having confidants was associated with DMS, and seldom feeling distressed was associated with lower odds for DIS and PQS. In job stressors, job dissatisfaction was associated with DMS. Poor human relations in the workplace and longer hours worked overtime were associated with PQS. In addition, workers in younger age groups reported more job stressors and worked extra hours compared to their older counterparts (Table 6). 4. Discussion Psychological factors, such as higher perceived stress or not considering their life meaningful or worth living (ikigai), were associated with all types of insomnia even after controlling for possible confounders such as blood pressure, BMI, medical treatment, and lifestyle-related factors. Recent studies conducted in the Japanese workplace demonstrated a strong association between psychological job stress and insomnia [7,14]. Another study in Finland reported the effects of stress in daily life, such as family problems, on insomnia in a community population [15]. Although the cross-sectional nature of our study makes definite conclusions on causation difficult, the association of psychological factors with insomnia seems to be strong. One explanation might be stress. A study in Sweden indicated that although working under high demands was a risk factor for insomnia, not high demands per se but the effect on unwinding after work causes sleep problems. The authors suggested that the inability to free oneself of thoughts of work during leisure time might explain such an association [11]. Although we did not limit the stress to being workrelated when asking the question, observed association of job stressors with insomnia seemed to be mediated by perceived stress since the association of job stressors with insomnia was attenuated substantially when perceived stress was entered into the model (data not shown). To confirm the association, we conducted additional multiple regression analyses with perceived stress as a dependent variable. All the job stressors except for underutilization of skills were significantly associated with higher perceived stress. High demand, poor human relations in the workplace, low job control, low job satisfaction, and poor physical environment in the workplace predicted 10.9%, 2.3%, 1.8%, 0.5%, and 0.1% of variances in perceived stress, respectively. To interpret the association between perceived stress and insomnia, we may need to consider personal traits as well, since not every person responds to a stress in
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the same way. In fact, those who answered that they seldom felt distressed had lower odds for PQS compared to those who felt distressed but had a confidant. This may indicate that in occupational settings merely eliminating job stressors may not be sufficient, but psychological interventions such as teaching human relation skills or stress management techniques may also be required. A review reported that a psychotherapeutic approach improved sleep quality of patients in various studies [6]. In the current study, a higher rate of PQS was observed among younger workers. The explanation might be longer working hours compared to their older counterparts. As shown in Table 6, those in the 35- to 44-year-old age group worked longer hours per day and reported more job stressors compared to other age groups. Additional analyses indicated that those who worked overtime slept significantly (p < 0.001) fewer hours (mean: 6.37 h) than those who did not do so (mean: 6.74 h). There is a report indicating that overtime work is a risk factor for acute myocardial infarction [16] as well as for depression [17]. We need to further investigate the association between long work hours and health problems more seriously. Poor human relations in the workplace were also associated with PQS. A study conducted in the Japanese workplace suggested that in Asian cultures where harmony in human relations is valued, human relations in the workplace may have a strong impact on job-related stress [7]. Another study in Sweden reported that those with more social support had lower risk of insomnia, indicating that social support had an effect on the reduction of sleep problems [11]. Somatic conditions such as past hospitalization or treated hyperuricemia were associated with DMS among our population. In a study in Finland, those hospitalized during the previous 5 years reported more insomnia [15]. Some medication stimulates patients and often causes early morning awakening or arousal during the night [6]. In age-adjusted models, receiving treatment for hypertension was associated with DIS and DMS. Current diabetes, hyperuricemia, and hyperlipidemia were associated with DMS (Table 2). It is possible that medication constitutes a cause of insomnia, especially among those reporting DIS and DMS. Sleep apnea is often pointed to as a cause of insomnia [18]. In this study, we did not ask if respondents had excessive daytime sleepiness or fatigue, symptoms of sleep apnea that are well-known risk factors for insomnia, nor did we ask if respondents snore during the night. However, the effect of sleep apnea may be relatively small in our population since the degree of obesity as measured by BMI, a major risk factor of sleep apnea, was not associated with insomnia in the preliminary analyses. Lastly, we should touch upon some limitations in our study. Depression was not assessed among our
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population. Although considering life meaningful and worth living (ikigai) was associated with insomnia, we could not rule out the possibility that those who reported insomnia already suffered from depression. A study reported a depression rate of as much as 38.6% among the working population in Japan [19]. Since studies have reported a higher incidence of depression among insomniacs [6,17], we need to consider mental health problems more seriously in dealing with insomnia. For that, sleep complaints may serve as a useful indicator to identify those under stress and at risk of developing mental problems such as depression. Another limitation is that insomnia was assessed based on self-report only. Although a study concluded that self-reported insomnia was independent of poor sleep as measured by electroencephalography and that sleep complaints were not always concordant with such objective measures [20], the association of sleep complaints with objective sleep quality needs to be investigated in detail in future studies. In addition, depression and anxiety need to be measured for effective interventions. Finally, insomnia was assessed based on three questions with binary responses (yes or no). This may have contributed to the higher prevalence of insomnia among our study population. To identify cases of insomnia, we need to use validated instruments such as the Japanese version of the Pittsburgh Sleep Quality Index (PSQI-J) [21] or the diagnostic criteria of the ICD-10 [4] with information about the time and duration of symptoms. 5. Conclusions Due to the above-mentioned limitations, reaching a definite conclusion about the relationship between psychological factors and insomnia might be difficult. Nonetheless, this study indicated that psychological factors, such as not considering life meaningful or worth living (ikigai), not having someone to talk to when distressed, and higher perceived stress, were related to all types of insomnia, even after adjusting for possible confounders. In addition, poor human relations in the workplace and longer work hours were related to PQS in which younger age groups were disproportionately at risk in our population. Our results suggest the importance of considering psychological factors in addition to somatic conditions in dealing with insomnia among working populations. Acknowledgements This study was supported in part by grants from the Ministry of Education, Culture, Sports, Science and Technology and the Japan Atherosclerosis Prevention Fund (JAPF).
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