Association between nighttime and daytime ambient temperature and insomnia using national emergency department database in the capital city of South Korea.

Insomnia is a growing health concern globally, with significant implications for public health. Most studies have primarily focused on the effects of nighttime temperatures on sleep problems. However, there is a lack of studies comparing nighttime temperatures with daytime temperatures, which are more closely related to daily life activities. This study aimed to explore a short-term association of nighttime and daytime ambient temperature with emergency department (ED) visits for insomnia in the capital city of South Korea. A time-stratified case-crossover design was employed using a conditional logistic regression model. A distributed lag non-linear model was utilized to explore potential non-linear and lag effects of ambient temperature on ED visits for insomnia. Odds ratio (OR) for temperature with maximum ED visits for insomnia (MaxIT) and that for temperature with minimum ED visits for insomnia (MinIT) were calculated and compared. We observed significant associations at high temperatures for both nighttime and daytime (nighttime: 25.0℃ (94.1%) [OR: 1.82, 95% CIs: 1.31-2.55], daytime: 30.6℃ (99.0%) [OR: 2.13, 95% CIs: 1.49-3.06]) compared to MinIT (-8.5℃ (2.7%) and - 8.4℃ (1.0%), respectively). Subgroup analyses found significant associations at high temperatures in females, individuals aged 35-49, and those without comorbidities, and during spring, fall, and winter, for both daytime and nighttime. Our findings provide insights for proactive public health strategies for managing insomnia during global temperature rise.