Lifestyles and sleep disorders among the Japanese adult population
Keiko Kim MDDepartment of Psychophysiology, National Institute of Mental Health, National Center of Neurology and Psychiatry, 1-7-3 Kohnodai, Ichikawa-City, Chiba 272, Japan.
To clarify the effects of daily stress, habitual exercise, drinking and smoking on the prevalence of sleep disorders, we selected 4000 residents (≥ 20 years) in Japan by stratified random sampling and carried out structured interviews (response rate 75.8%). Frequencies of sleep disorders (difficulty initiating sleep: DIS; difficulty maintaining sleep: DMS; early morning awakening and hypnotic medication use) were treated as dependent variables. Significant effects of stress were prevalent in all sleep disorders. Habitual exercise had significant negative association with DIS and DMS. Drinking and smoking did not affect sleep disorders.
Sleep disorders are among the commonest of health problems. In the USA, sleep complaints are prevalent in approximately one-third of the population.2 Several studies have reported that habitual lifestyle is related to the prevalence of sleep disorders.1,2,5 However, no studies have assessed the prevalence of sleep disorders among the general population in Japan. We investigated the effects of habitual lifestyle on the prevalence of sleep disorders among the adult Japanese population.
Questions about sleep states were included in a community health survey conducted during February and March of 1997 by the Japan Health Promotion and Fitness Foundation. The survey population consisted of individuals aged 20 years or over resident in Japan. Randomly sampling from sociodemographically stratified cohorts of residents (20 regional block groups selected according to geographical location and city size (Table 1)), we obtained 4000 individuals. Proportionate samples of households were taken within block groups, as defined by the Japan Census (1997). First, we sent letters that asked for the residents’ consent to participate. Carefully trained interviewers conducted their interviews at the residences selected for the survey. Finally, we completed the survey based on data for 3030 individuals (response rate 75.8%).
Table 1. .
Demographic characteristics of survey sample and the Japanese population
The questionnaire contained 59 individual items. In the present study we used sex and age as demographic variables. We used the following four items as independent variables: presence or absence of daily stress; participation or non-participation in habitual exercise; drinking or non-drinking; and smoking or non-smoking. We excluded subjects who had recently stopped drinking or smoking. Four questions about sleep disorders were included in the study as dependent variables: (1) ‘Do you have difficulty falling asleep at night?’: Difficulty initiating sleep (DIS). (2) ‘Do you wake up during the night after you have gone to sleep?’: Difficulty maintaining sleep (DMS). (3) ‘Do you wake up too early in the morning and have difficulty getting back to sleep?’: Early morning awakening (EMA). (4) ‘Do you take any kinds of medication or use alcoholic beverages to help you sleep?’: Hypnotic medication use (HMU).
Each question had five possible replies: ‘never’, ‘seldom’, ‘sometimes’, ‘often’, and ‘always’. ‘Often’, or ‘always’ was taken as an affirmative answer.
Statistical analysis was performed using chi-squared test. Differences at P < 0.05 were considered statistically significant.
The subjects with stress showed more frequent DIS (chi-squared = 56.73, P = 0.001), DMS (Chi-squared = 29.06, P = 0.001), EMA (Chi-squared 2 = 12.27, P = 0.001), and HMU (Chi-squared = 59.99, P = 0.001). Habitual exercise affected DIS (chi-squared = 10.95, P = 0.001) and DMS (Chi-squared = 8.37, P = 0.005), but had no effect on EMA and HMU. With respect to drinking and smoking, there were no significant effects on the prevalence of sleep disorders.
In this study, individuals with stress were subject to DIS, DMS, EMA, and HMU. No previous studies have investigated the effect of stress on sleep disorders in the general population, although a high prevalence of sleep disorders among subjects suffering severe stress, such as post-traumatic stress disorder, was well documented. This paper provides the first documented evidence that stress is associated with various kinds of sleep disorder among the general adult population. We found less frequent DIS and DMS among subjects taking habitual exercise. There have been no general population studies on the relationship between habitual exercise and sleep disorders. Several experimental studies have indicated that exercise in the daytime promotes better sleep.4 These results suggest that taking habitual exercise might prevent sleep disorders to some extent. In the present study, smoking and drinking habits did not appear to affect sleep disorders. Few studies have linked smoking with sleep disorders, but other studies were unable to find any relationship between the two.2,3