Circadian Rhythm Assessment and Melatonin Dynamics

Circadian rhythms are endogenous, near-24-hour cycles that orchestrate physiological and behavioural functions, synchronising sleep–wake patterns, hormone secretion and metabolic processes to the environmental light–dark cycle. Central to this system is the suprachiasmatic nucleus, which drives rhythmic release of melatonin by the pineal gland. Melatonin dynamics—its onset, amplitude and duration—serve as reliable biomarkers of circadian phase and amplitude. Traditional laboratory assessments of circadian phase rely on protocols such as the dim light melatonin onset (DLMO), requiring controlled lighting, frequent sampling and precise assay methods. Advances in wearable technologies, computational modelling and at-home collection protocols have expanded the toolkit for rhythm assessment, enabling scalable, non-invasive measurement in real-world settings. These approaches facilitate personalised chronotherapeutics, optimisation of shift-work schedules and early diagnosis of circadian rhythm sleep–wake disorders. Together, they underpin efforts to translate circadian biology into clinical practice and public health strategies aimed at improving sleep, cognitive performance and metabolic health worldwide.

Research from Nature Portfolio

Mathematical modelling has provided a quantitative framework for understanding how altered light‐dark exposure and social constraints precipitate circadian misalignment. One study developed a model integrating light input, circadian oscillators and sleep homeostasis, revealing that evening light consumption delays the internal clock and that enforcing fixed wake-times generates ‘social jet-lag’. The model predicted that reducing evening light is more effective than shifting social schedules, particularly in adolescents with slow intrinsic clocks. In parallel, application of a limit-cycle oscillator model to field data from rotating shift workers demonstrated that ambulatory light and activity measurements can predict melatonin phase with sub-one-hour accuracy in most individuals. Although inter-individual variability in phase shifts remains a challenge, these findings confirm that model-based estimations of circadian phase can be generalised to real-world shift-work settings and form the basis for adaptive scheduling interventions.

Circadian Rhythm Assessment and Melatonin Dynamics publication trend

The graph below shows the total number of articles in circadian rhythm assessment and melatonin dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

Circadian rhythm: Endogenous oscillation with a period of approximately 24 hours, governing physiological and behavioural cycles.

Dim Light Melatonin Onset (DLMO): The time at which melatonin concentration in saliva or plasma rises above a threshold under dim light conditions, marking circadian phase.

Actigraphy: A non-invasive method using wrist-worn sensors to record movement and infer rest–activity cycles over extended periods.

Acrophase: The time point of the peak of a rhythmic cycle, often applied to hormone secretion or activity levels.

Limit-cycle oscillator model: A mathematical representation of the circadian pacemaker as a self-sustained oscillator driven by light and behavioural inputs.

Chronotype: An individual’s propensity to sleep and wake at particular times, often categorised as ‘morning’ or ‘evening’ preference.

References

1. CARE as a wearable derived feature linking circadian amplitude to human cognitive functions. npj Digital Medicine (2023).
2. A Protocol to Determine Circadian Phase by At‐Home Salivary Dim Light Melatonin Onset Assessment. Journal of Pineal Research (2024).
3. The effects of self-selected light-dark cycles and social constraints on human sleep and circadian timing: a modeling approach. Scientific Reports (2017).
4. Application of a Limit-Cycle Oscillator Model for Prediction of Circadian Phase in Rotating Night Shift Workers. Scientific Reports (2019).
5. The dim light melatonin onset across ages, methodologies, and sex and its relationship with morningness/eveningness. Sleep (2023).