Dim light melatonin onset (DLMO): clinical and methodological aspects

The circadian rhythm of melatonin in plasma or saliva is a defining feature of the endogenous oscillatory pacemaker function, the suprachiasmatic nucleus, A substantial number of studies have shown that, within this rhythmic profile, the onset of melatonin secretion under dim light conditions (the dim light melatonin onset or DLMO) is the single most accurate marker for assessing the circadian pacemaker. Additionally, melatonin onset has been used clinically to evaluate problems related to the onset or offset of sleep. This chapter discusses the relationship between endogenous melatonin and sleep, the clinical significance of DLMO for diagnosing circadian rhythm sleep disorders, and the available techniques to assay melatonin. The chapter is based on parts of earlier publications on DLMO added with a PubMed literature search using DLMO and human as the keywords.