The Dim Light Melatonin Onset (DLMO) across ages, methodologies and sex and its relationship with Morningness/Eveningness.

The onset of melatonin secretion, the Dim Light Melatonin Onset or DLMO is a tool for determining the phase of the circadian timing system. While small studies have investigated the impacts of age and methods of calculating DLMO, there is no DLMO reference range. In the current study, the saliva DLMO from 121 published studies (3579 subjects) and plasma DLMO in 31 studies (818 subjects) in healthy control subjects (3 - 73 years) were analysed. In a subset of 53 papers (1749 subjects) individual saliva DLMO and MEQ scores were obtained from authors or mined from publications and a reference range was constructed. Saliva DLMO was earliest in children to 10 years of age and latest around 20 years of age and thereafter advanced with age by 30 minutes in the oldest subjects. Melatonin assay methods and DLMO calculation methods had little effect on the determination of the DLMO. Saliva DLMO was correlated (P < 0.001) with the MEQ score; lower MEQ scores were associated with later DLMO. MEQ scores increased with age, reflecting a tendency towards Morningness. An evaluation of 14 saliva DLMO studies of clinically diagnosed DSWPD patients (mean ages 20 to 31 years) revealed mean saliva DLMO within the reference range albeit at the late extreme. Peak plasma melatonin levels from 179 studies of healthy subjects revealed a high degree of variability within studies and age groups, but only a small decline between the 20 and 50 years and lowest levels after 70 years.