Relationship between dim light melatonin onset and the timing of sleep in sleep onset insomniacs

Abstract

Dim light melatonin onset (DLMO), a phase marker of the circadian system can be estimated from sleep diaries of good sleepers. Previous studies have shown a strong relationship between DLMO and midpoint of sleep and wake-up time. The present study investigated these same relationships in a group of sleep onset insomniacs. The correlations between DLMO and sleep onset time, sleep midpoint and wake-up time were significant but only moderate at r = 0.43, 0.48 and 0.42, respectively. Further, when the group was divided into insomniacs with late and early DLMO the correlations for the early group were no longer significant. Caution should be exercised when predicting DLMO from the sleep times of insomniacs.