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ORIGINAL ARTICLES |
From the Department of Psychophysiology (K.K., M.U., X.L., K.S.), National Institute of Mental Health, National Center of Neurology and Psychiatry, Chiba, Japan; Department of Psychiatry (X.L.), Shandong University, Shandong, People’s Republic of China; Department of Public Health Administration (T.O.); National Institute of Public Health, Tokyo, Japan; Japan Health Promotion and Fitness Foundation (R.O.), Tokyo; and Department of Psychiatry (M.O.), Shiga University of Medical Science, Shiga, Japan.
Address reprint requests to: Makoto Uchiyama, MD, Department of Psychophysiology, National Institute of Mental Health, National Center of Neurology and Psychiatry, 1-7-3 Kohnodai, Ichikawa-city, Chiba 272-0827, Japan. Email: macoto{at}ncnp-k.go.jp
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ABSTRACT |
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METHODS: We randomly selected 4000 adult residents (
20 years old) from five areas of Japan using stratified sampling and conducted interviews using a structured questionnaire. The questionnaire solicited information about eight somatic symptoms, eight psychological symptoms, three sleep problems, and demographic and health-related information. A total of 3030 subjects completed questionnaires, giving a response rate of 75.8%.
RESULTS: Stiff neck/shoulder (45.3%), backache (35.1%), and fatigue (31.4%) were the most common complaints in this population. In general, SPCs were more prevalent in younger persons and in women. Logistic regression analyses, controlling for other factors, showed that insomnia was significantly associated with a number of SPCs: backache (odds ratio [OR] = 1.4, 95% confidence interval [CI] = 1.1–1.6), epigastric discomfort (OR = 1.7, 95% CI = 1.3–2.2), weight loss (OR = 2.0, 95% CI = 1.2–3.3), headache (OR = 1.7, 95% CI = 1.3–2.2), fatigue (OR = 1.7, 95% CI = 1.4–2.1), worrying (OR = 1.6, 95% CI = 1.1–2.3), irritability (OR = 1.4, 95% CI = 1.1–1.7), and loss of interest (OR = 1.8, 95% CI = 1.2–2.7).
CONCLUSIONS: SPCs were common and were largely associated with insomnia in the general adult population of Japan. Further study is needed to examine the causal links between SPCs and insomnia.
Key Words: somatic and psychological complaints • insomnia • cross-sectional study • general population.
Abbreviations: CI = confidence interval; OR = odds ratio; SPCs = somatic and psychological complaints.
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INTRODUCTION |
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SPCs are also common in the general population. Hammond (5) reported that the prevalence of somatic complaints ranged from 0.4% to 56.2% in a large sample of Americans. Escobar et al. (6) reported that somatization symptoms occurred in approximately 4% of the general population. In a sample of 13,538 individuals interviewed in the Epidemiologic Catchment Area Program, Kroenke et al. (7) found that physical symptoms had been a problem for more than 10% of people at some point in their life. The large variance in prevalence seems to be due to methodological differences, including case definition, case assessment, and target population.
Insomnia was associated with depressive disorders and other SPCs in young adults in the Zurich study (8). Motohashi et al. (9) reported that sleep habits were associated with psychosomatic complaints of bank workers in Japan. However, there may be considerable sampling bias in these studies because of limited survey populations. Mellinger et al. (2) reported that people with serious insomnia tend to report more anxiety, psychic distress, symptoms resembling major depression, and multiple health problems than people without insomnia. However, the authors did not consider individual symptoms, and they did not control for confounding factors such as sociodemographic factors. The association between SPCs and insomnia in the general population has not yet been systematically investigated.
The current epidemiological study was conducted to estimate the prevalence of SPCs and to examine the association of SPCs with insomnia in a large sample from the general population of Japan.
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METHODS |
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The sampling and procedures, which were described in detail in our previous reports (10, 11), are summarized here.
First, the country was divided into five geographical regions: north, east, middle, west, and south. Next, a big city (population >1,000,000), a middle-sized city (population >150,000), a small city (population <150,000), and a town or village (population <50,000) were drawn randomly from each target region.150,000 but A total of 4000 subjects aged 20 years or older were selected randomly from the house register in the targeted cities, towns, and villages in proportion to the general adult population.
We sent the subjects a letter containing information about the purpose of the survey and a request to participate. After the subjects had given their informed consent, they were interviewed in their homes by well-trained interviewers who had already participated in several national health surveys. Finally, 3030 subjects were interviewed, giving a response rate of 75.8%.
Measures
A structured questionnaire was developed. The questionnaire contained questions about sociodemographic characteristics plus 52 questions about SPCs, including 8 about somatic complaints, 8 about psychological complaints, and 3 about sleep problems.
Experience of an SPC during the previous month was indicated by an answer of yes or no. Somatic complaints included backache, stiff neck/shoulder, epigastric discomfort (including appetite loss), tachycardia/dyspnea, weight loss, headache, dizziness, and fatigue. Psychological complaints included difficulty concentrating, weariness, worrying, irritability, overcrowded mind, loneliness, loss of interest, and concern about health.
The following three questions about insomnia experienced during the previous month were embedded in the questionnaire: 1) "Do you have difficulty falling asleep at night?" (difficulty initiating sleep); 2) "Do you wake up during the night after you have gone to sleep?" (difficulty maintaining sleep); and 3) "Do you wake up too early in the morning and have difficulty getting back to sleep?" (early morning awakening). Each question had five possible replies: never, seldom, sometimes, often, and always. Often and always were taken as an affirmative answer to the question. The presence of difficulty initiating sleep, difficulty maintaining sleep, and early morning awakening was defined when affirmative answers were given in response to questions 1, 2 and 3, respectively. The presence of insomnia was defined as an affirmative answer for any of the three questions.
The sociodemographic variables were sex, age (younger adult, 20–39 years; middle-aged adult, 40–59 years; older adult, 60 years and older), marital status (married or single), education (college, junior college, or above; high school, middle, or elementary school), and occupation (employed or unemployed).
Statistical Analysis
2 tests were used for categorical data such as prevalence of individual SPCs by gender and age.
A series of logistic regression analyses was performed to explore the association of SPCs with insomnia. All variables were initially examined in univariate models. We then performed multivariate logistic regression analyses to adjust for the confounding effects of sociodemographic factors such as age, sex, education, marital status, and occupation. The final multivariate logistic regression analyses were performed to control for all sociodemographic and other factors.
All analyses were performed using SPSS 8.0 for Windows 98.
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RESULTS |
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2 = 6.40, p < .01). Table 2 shows the prevalence of individual SPCs by age and sex. Three somatic complaints, stiff neck/shoulder (45.3%), backache (35.1%), and fatigue (31.4%), were highly prevalent. Stiff neck/shoulder, headache, dizziness, fatigue, worrying, and irritability were more common in women than in men (p < .01).
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In women, stiff neck/shoulder, headache, fatigue, and difficulty concentrating were more prevalent in the younger- and middle-aged groups than in the older-aged group (p < .01). Epigastric discomfort and dizziness were more frequent in the younger-aged group (p < .05 and p < .01, respectively).
Tachycardia/dyspnea was most frequent in the older-aged group for both men and women (p < .01).
Psychological complaints were prevalent in the younger-aged group, but concern about health was prevalent in the elderly.
Association of SPCs With Insomnia
The overall prevalence of insomnia was 21.4%. The prevalence of insomnia in those with and without SPCs was 24.1% and 10.9%, respectively, a significant difference (2 = 53.1, p < .01).
The prevalence of insomnia increased significantly with the number of SPCs, as indicated in Table 3. Logistic regression analysis revealed a significant "dose effect" of the number of SPCs on insomnia after adjusting for sociodemographic factors.
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DISCUSSION |
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Wool and Barsky (15) suggested five possible mechanisms of gender differences in somatization symptoms. These include gender differences in willingness to admit to discomfort, readiness to seek medical attention, and the prevalence of psychiatric disorders with prominent somatic features; innate differences between men and women in their threshold, tolerance, and sensitivity to minor bodily sensation; and differences in relational patterns.
Young people reported more SPCs than did the elderly except for tachycardia/dyspnea, weight loss, and concern about health. These results, obtained with individual 2 tests, might have included chance findings; however, they were rather surprising because it might have been expected that medical condition and physiological factors would have been strongly associated with age and therefore that somatic complaints would increase with age. However, this finding is consistent with Koenig and Blazer’s (16) observation, in a comparison of younger and older Epidemiologic Catchment Area subjects by symptom frequency, that both somatic and psychological symptoms decrease in old age. Potential age-related factors such as lifestyle, daytime activity, or cognitive capacity might be taken into consideration in future investigations.
The overall prevalence of insomnia was 21.4%, which is comparable to rates reported in Western countries (1, 3, 9, 17–21). The prevalence of insomnia showed a significant positive correlation with an increasing number of SPCs. Among individual SPCs, backache, epigastric discomfort, weight loss, headache, fatigue, worrying, irritability, and loss of interest were independently associated with a risk of insomnia after adjusting for confounding effects of other independent variables. This finding is in contrast to that of the Zurich study, which found that insomnia was not associated with syndromes causing physical pain (eg, backache or headache) (8). Because frequency of symptoms was assumed to be higher than that of syndromes, it is possible that the Zurich study did not detect pains themselves.
Although the results of many previous studies have suggested that general health and mental health problems are related to insomnia, the populations included in such studies were specific and generally small (3, 5, 8, 9, 17, 20–22). The current epidemiological study was conducted to examine the association of SPCs with insomnia in a large sample from the general population of Japan. In our cross-sectional study, it was difficult to determine the causal links between SPCs and insomnia (ie, whether insomnia causes daytime dysfunction and SPCs or whether a somatic or psychological disorder disturbs sleep).
There are several possible explanations for the association of insomnia with SPCs. First, insomnia may be caused by SPCs stemming from psychological stress. There is evidence that a number of physical and psychological symptoms are associated with an increased risk of insomnia (1, 3, 5, 9, 17, 20–22). In addition, individuals who have psychophysiological insomnia are widely believed to react to stress with somatized tension and agitation (23).
Second, insomnia may be a cause of SPCs. Insomnia is likely to cause chronic sleep disruption or sleep deprivation (24, 25). Previous studies have demonstrated that sleep deprivation has wide adverse effects on psychological and physical functions and on daytime activity and alertness (26, 27). A recent study found that experimental subchronic sleep curtailment reduced glucose tolerance and serum thyrotropin concentrations, raised evening cortisol concentrations, and increased the activity of the sympathetic nervous system, suggesting that loss of sleep can cause an imbalance in hormone production or autonomic function. This, in turn, might lead to psychological and somatic complaints even if such complaints were not severe enough to establish a clinical entity or syndrome (28).
Third, the significant association may be due to high comorbidity between insomnia and SPCs. Both insomnia and SPCs may be caused by a number of the same psychosocial factors, such as acute or chronic life stress, physical diseases, and adverse environmental conditions. On the other hand, both insomnia and SPCs could be different manifestations or symptoms of some diseases, such as depression, anxiety disorders, diabetes, or cardiovascular diseases.
Because the present study was cross-sectional, no causal relationship between insomnia and SPCs can be established. Additionally, SPCs and insomnia were based on self-reporting, and that could have biased the findings. However, complaints of insomnia are not always concordant with objective measures. Insomniacs’ estimates about their sleep are often disparate from polysomnographic data (29). The crucial question of whether insomnia causes SPCs or vice versa should be addressed in future studies.
In summary, a large sample of the Japanese general population was investigated with a structured questionnaire. Approximately 79% of the sample reported at least one SPC during the previous month. Somatic and psychological symptoms were more prevalent in younger subjects and in women. SPCs seem to have a strong association with insomnia in the Japanese general population.
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ACKNOWLEDGMENTS |
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Received for publication March 15, 2000.
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