Differences in insomnia-related factors between working-age and older adults: A comparison of nocturnal and daytime symptoms.

Objective: This study aimed to (1) clarify the characteristics of nocturnal and daytime symptoms among working-age and older adults and (2) classify insomnia types within each age group and examine the characteristics associated with each type. Methods: An online survey was conducted, and data from 1655 participants were analyzed. Participants were categorized into working-age adults (30-64 years) and older adults (≥65 years). Based on the presence or absence of nocturnal symptoms and daytime dysfunction according to the International Classification of Sleep Disorders, Third Edition criteria, participants were classified as normal sleepers, having subsyndromal insomnia, or having insomnia syndrome. Nocturnal and daytime symptoms were assessed using validated self-reported measures. Results: Compared with older adults, working-age adults showed significantly worse scores for all nocturnal and daytime symptoms. In working-age adults, subsyndromal insomnia was associated with sleep-wake characteristics, whereas insomnia syndrome was strongly associated with sleep debt, fatigue, and anxiety. Conversely, insomnia syndrome was primarily associated with sleep debt and fatigue among older adults. Notably, fatigue showed a greater discriminative ability than daytime sleepiness in distinguishing insomnia types across age groups. Conclusion: The nocturnal and daytime profiles associated with sleep problems differed between working-age and older adults. These findings suggest that age-specific assessment and treatment strategies are warranted and that fatigue may be a particularly important indicator when evaluating daytime dysfunction related to insomnia.