Sleep disturbance is associated with not only shorter sleep duration, but also longer time in bed: a Japanese general population survey

Abstract

Individuals with chronic insomnia tend to increase their amount of time in bed (TIB) to secure more opportunity for sleep, which in turn, may aggravate and perpetuate the condition. It remains unclear whether this behavioral feature of clinical insomniacs, which are targets of cognitive–behavioral therapy for insomnia, can be generalized to individuals with sleep disturbance in the general population. To investigate the relation between TIB and sleep disturbance in the general adult population, we conducted a cross-sectional survey with face-to-face interviews in August and September 2009. Data from 2559 randomly-sampled adults living in Japan were analyzed. Participants were asked about difficulty initiating sleep (DIS), difficulty maintaining sleep (DMS), early morning awakening (EMA), sleep duration, and TIB. Any sleep difficulties (ASDs) were defined as having DIS, DMS, and/or EMA. The associations between sleep difficulties (DIS, DMS, EMA, and ASDs) and hourly-stratified sleep duration and TIB were examined using logistic regression analyses. DIS, DMS, EMA, and ASDs were found to be associated with a sleep duration < 6 h. Furthermore, DIS, DMS, and ASDs were associated with a TIB ≥ 9 h. Sufferers of DIS, DMS, EMA, or ASDs had shorter sleep duration and longer wakefulness in bed compared with non-sufferers. To our best knowledge, this is the first epidemiological study reporting an association between prolonged TIB and sleep disturbance in the general population. Our findings suggest that optimizing TIB may be an important tactic to improve sleep disturbance in the general population.