Can a watch tell body clock time? Phase relationships between dim light melatonin onset and sleep markers determined from actigraphy, sleep diaries and the Munich Chronotype Questionnaire

Measurement of circadian phase (body clock timing) is often required for diagnosis and treatment of circadian rhythm disorders. However measurement of Dim Light Melatonin Onset (DLMO), the gold standard measure of circadian phase, is expensive and often impractical. As preferred timing of sleep reflects body clock timing, measurement of sleep markers provides a simple way to derive circadian phase. DLMO has been estimated from markers determined subjectively by questionnaires or sleep diaries; however actigraphy now provides the potential for objective and more accurate measurement of sleep markers. The aim of this study is to compare the phase differences between DLMO and sleep markers determined objectively by actigraphy, and subjectively by sleep diaries and the Munich ChronoType Questionnaire (MCTQ).