Nationwide epidemiological study of insomnia in Japan.
This study was a nationwide epidemiological study of insomnia in Japan. It was conducted because very few studies on this topic have previously been performed for the general Japanese population.



An interview survey on symptoms of insomnia (difficulty initiating sleep, difficulty maintaining sleep with difficulty resuming sleep, and early morning awakening with difficulty resuming sleep) and daytime dysfunction was conducted on the general nationwide population in the winter (February) and summer (August) of 2008. Data from 2614 participants who provided valid responses (age range 20-95 years, valid response rate 54.2%) were analyzed.



The prevalence of difficulty initiating sleep, difficulty maintaining sleep with difficulty resuming sleep, and early morning awakening with difficulty resuming sleep was 8.3%, 5.8%, and 5.8%, respectively, in men, and 11.0%, 8.1%, and 7.4%, respectively, in women. The prevalence of insomnia was 12.2% in men and 14.6% in women, and the prevalence of insomnia with daytime dysfunction was 3.2% in men and 4.2% in women. The results of logistic regression analyses indicated that the factors aggravating insomnia for men were unemployment and having mental health issues, and for women they were being aged ≥70 years, completing fewer years of schooling, and having mental health issues. Seasonality and regionality in association with insomnia were also examined, but no significant associations were found.



In the present survey, insomnia was defined by using criteria that were closer to the clinical diagnostic criteria (eg, coexistence of both difficulty resuming sleep and daytime dysfunction was considered). Therefore, it is believed that the results of this study were representative of the clinical actuality of insomnia in Japan.
Department of Public Health and Epidemiology, Faculty of Medicine, Oita University, Oita, Japan.
Osamu
O
Itani
Department of Public Health and Epidemiology, Faculty of Medicine, Oita University, Oita, Japan. Electronic address: nusmpublichealth@gmail.com.
Yoshitaka
Y
Kaneita
Socio-Tech Institute Co., Ltd., Tokyo, Japan.
Takeshi
T
Munezawa
National Center of Neurology and Psychiatry, Tokyo, Japan.
Kazuo
K
Mishima
Division of Public Health, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan.
Maki
M
Jike
Division of Public Health, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan.
Sachi
S
Nakagome
Department of Public Health and Epidemiology, Faculty of Medicine, Oita University, Oita, Japan.
Mikiko
M
Tokiya
Division of Public Health, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan.
Takashi
T
Ohida
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002940:Circadian Rhythm; D016021:Epidemiologic Studies; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012621:Seasons; D007319:Sleep Initiation and Maintenance Disorders / Q000175:diagnosis / Q000453:epidemiology*; D011795:Surveys and Questionnaires
Associated factors; Prevalence; Region; Season; Summer; Winter