The endogenous melatonin profile as a marker for circadian phase position

Area of Science:

• Chronobiology
• Neuroendocrinology
• Sleep Medicine

Background:

• Circadian rhythms are crucial for assessing the endogenous circadian pacemaker (ECP).
• Discrepancies arise when multiple marker rhythms are used, raising questions about oscillator reliability and masking.
• Dim-light melatonin onset (DLMO) is a convenient marker, but low melatonin production can complicate its assessment.

Purpose of the Study:

• To evaluate various plasma melatonin profile markers for circadian phase assessment.
• To investigate the influence of melatonin production amplitude on phase markers, particularly in low melatonin producers.
• To compare the reliability of dim-light melatonin offset (DLMOff) and melatonin synthesis offset (SynOff) as phase markers.

Main Methods:

• Analysis of plasma melatonin profiles in 14 individuals, including several low melatonin producers.
• Evaluation of different operational thresholds for dim-light melatonin onset (DLMO).
• Comparison of DLMOff and SynOff, considering the impact of melatonin amplitude.

Main Results:

• Melatonin production amplitude significantly influences many points on the melatonin profile.
• A lower DLMO threshold (below 10 pg/ml) is recommended for low melatonin producers.
• DLMOff appears confounded by amplitude, suggesting SynOff is a more reliable marker, unaffected by amplitude and theoretically closer to the offset mechanism.

Conclusions:

• Adjusting DLMO thresholds is necessary for accurate circadian phase assessment in low melatonin producers.
• Melatonin synthesis offset (SynOff) is a more robust marker than DLMOff due to its independence from melatonin amplitude.
• Findings contribute to optimizing the use of melatonin profiles for determining human circadian phase position.