Morning sleep inertia and its associated factors: Findings from a nationwide study

Sleep inertia, a transitional state of grogginess and impaired alertness upon awakening, varies in duration and influencing factors. This study examined its characteristics and associations with sociodemographic factors, sleep patterns, and comorbidities in a Korean adult population.

Data from 2,355 participants (49.2% male, aged 19-92) in the Korean Sleep Headache Study (2018) was analyzed. Morning sleep inertia was assessed via self-reported duration in minutes using the question, "How long does it typically take for you to clear your grogginess in the morning after waking from overnight sleep?" While this single-item question was appropriate for a population-based study, it may not fully capture the multidimensional nature of sleep inertia. Multiple linear regression analyses were conducted using log-transformed sleep inertia as the dependent variable.

The mean (SD) sleep inertia was 15.8 (12.9) minutes. Females reported 1.1 minutes longer sleep inertia than males, although no significant differences were observed across age groups. Participants with anxiety reported 14.3 minutes longer inertia than those without anxiety, showing the largest effect size (Cohen's d = 1.12). Sleep inertia was negatively associated with sleep duration (beta [95% CI]: -0.05 [-0.07, -0.02]), morning chronotype (-0.16 [-0.24, -0.08]), and habitual snoring (-0.10 [-0.17, -0.02]), but positively associated with evening chronotype (0.12 [0.04, 0.19]), insomnia (0.22 [0.13, 0.30]), excessive daytime sleepiness (0.10 [0.02, 0.19]), and anxiety (0.39 [0.14, 0.63]) (p < 0.02 for all).

Sleep inertia was associated with sleep duration, chronotype, sleep-related symptoms, and anxiety. These findings underscore the need for targeted interventions to alleviate the adverse impact of sleep inertia on daily functioning.