Objective:

To integrate clinical, measurement, mechanistic, and intervention evidence on circadian dimensions in insomnia disorder and propose a candidate circadian phenotyping framework for future validation.

Approach:

• Review Methodology: The article is a narrative review that develops a phenotype-stratified research framework, utilizing searches from PubMed, Web of Science, and Google Scholar.

Key Findings:

• Insomnia disorder is characterized by difficulty initiating or maintaining sleep and is prevalent among individuals with mental health disorders.
• Circadian factors such as misalignment between endogenous circadian phase and intended sleep window may contribute to insomnia symptoms.
• Some patients exhibit delayed sleep timing, reduced rest-activity amplitude, and abnormal light exposure patterns.
• Cognitive behavioral therapy for insomnia (CBT-I) remains the first-line treatment.
• The review proposes a framework combining various assessment methods to distinguish different insomnia phenotypes.

Interpretation:

The findings suggest that circadian factors may act as modifiers of insomnia symptoms and treatment responses, rather than being a unified cause.

Limitations:

• The review does not provide a systematic review or clinical guidelines.
• Conclusions are based on narrative synthesis without formal risk-of-bias assessment or quantitative synthesis.

Conclusion:

The review translates circadian evidence in insomnia into testable propositions and emphasizes the need for phenotype-stratified trials.