Epidemiological Study on Insomnia and Depression Using Home Sleep Monitors in a Japanese Rural City Population

Depression is a major global public health problem and is projected to carry an even greater burden of disease worldwide in the coming decades. Both insomnia and excessive daytime sleepiness (EDS) are sleep disturbance that commonly occur as a principal component of depression. However, studies analyzing objective measurements of EDS or insomnia were very limited. Multiple sleep latency test (MSLT, four nap studies under polytrophic recordings in sleep labs) in psychiatric diseases demonstrated highly heterogeneous results. This may come from most studies had small sample size, which is frequently associated with both depressive symptoms and sleepiness.

Full polysomnography (full-PSG) provides comprehensive information about sleep duration and architecture, but it is too expensive and too cumbersome for large-scale or repeated-measures evaluations (¥96,380/case by Diagnosis Procedure Combination/Per-Diem Payment System in Japan). Using in-laboratory full-PSG as the gold standard has limitations in validity, partly because participants tend to sleep more poorly in the laboratory than at home. Thus, full-PSG may be unsuitable for screening large populations or for repeated evaluations. Actigraphy is a simple method for monitoring locomotor activity and can be used to estimate sleep/wake time but cannot access sleep architecture and sleep staging. Recent advances in electronic technologies and sensor interfaces have enabled small sleep portable monitors. The investigators compared a newly developed single-channel EEG monitoring system (SleepWell Co. Ltd., Osaka, Japan) with simultaneously recorded polysomnography. Single-channel EEG showed reasonable agreement with full-PSG (percent agreement and kappa coefficient of sleep stages were 86.9% ± 4.42 and 0.75 ± 0.081, respectively). This single channel EEG may be suitable to monitor daily sleep more easily in epidemiological settings.

Objective sleep monitoring is important. In measuring excessive daytime sleepiness, for example, subjective evaluation (Epworth sleepiness scale) failed to show much correlation with objective measurements with polygraph recordings. Individuals at high risk for depression have been found to have negative biases in processing information. They may answer subjective insomnia measurements more severely. Previous studies on depression and insomnia came mainly from subjective measures, which may be influenced by such negative evaluation bias. Objective sleep EEG measurements may be useful in overcoming such biases.

Sleep epidemiological study is limited in Japan. For example, sound estimates of prevalence of sleep apnea syndrome in Japan were lacking: previous Japanese studies have been limited by use of nonprobability samples, low response rates, small samples, and other methodologic problems. The investigators have performed sleep epidemiological study in a male working population in Japan. In the study, sleep apnea syndrome (apnea-hypopnea index (AHI) or respiratory event index (REI) ≥15) in males was estimated as 22.3%, which was similar to those in other studies including Sleep Heart Health Study. However, its target population included only Japanese "males". Studies in Japanese females are still missing.

In Japan, employers have to perform annual medical check-ups to their employees including detailed blood biochemical examination. Adding sleep survey to such annual examination, the investigators can analyze detailed physical effects of sleep with minimal costs. Even after the survey, with these annual examinations, the investigators can analyze incidences of lifestyle-related diseases (hypertension, diabetes, dyslipidemia, etc.) in the future.