Circadian Phase and Phase Angle Disorders in Primary Insomnia

Patients with insomnia had an average dim light melatonin onset time of 20:56 ± 1:55 hours, significantly later than the 22:02 ± 2:02 hours observed in healthy controls.

• Insomnia patients and controls attempted to sleep at similar clock times (24:17 ± 1:17 hours vs. 24:13 ± 1:30 hours, p = .84).
• Patients with insomnia slept at an earlier circadian phase than controls, with a phase angle of 2:13 hours (± 1:43) compared to 3:10 hours (± 1:08, p = .008).
• 10% of insomnia patients tried to sleep at or before their dim light melatonin onset, whereas no controls did.
• 22% of insomnia patients attempted to sleep before or within 1 hour after their dim light melatonin onset, compared to 6% of controls.
• These findings suggest that a significant proportion of insomnia patients may have a circadian phase misalignment contributing to their condition.

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