How does Dim Light Melatonin Onset (DLMO) relate to sleep onset time?

Relationship Between Dim Light Melatonin Onset (DLMO) and Sleep Onset Time

In individuals with normal circadian phase, DLMO typically occurs approximately 2-3 hours before habitual sleep onset time. 1

Understanding DLMO

DLMO is considered the gold standard marker for assessing human circadian phase and is defined as the time when melatonin levels begin to rise in the evening under dim light conditions. 1

• DLMO represents an approximation of the onset of melatonin synthesis and secretion 1
• It is the most commonly reported phase marker of the melatonin rhythm, though there is no standard definition of this measure 1
• Melatonin levels are typically very low during the day but begin to rise 1-3 hours before habitual sleep onset time 1

Methods of Determining DLMO

Three frequently used methods to determine DLMO from a partial melatonin profile include:

• An absolute threshold in the range of 2-10 pg/mL (typically 3 pg/mL for saliva or 10 pg/mL for plasma) 1
• A threshold calculated at 2 standard deviations above the average baseline (using 3 or more pre-rise samples) 1
• A visual estimate of the point of change from baseline to rising levels 1

Relationship with Sleep Parameters

Research has established specific relationships between DLMO and sleep timing:

• Wake time and midpoint of sleep show stronger correlations with DLMO (r = 0.77 and r = 0.68 respectively) than bedtime (r = 0.36) in young healthy individuals 2
• In individuals with free (ad libitum) sleep schedules, DLMO correlates more strongly with sleep times (r = 0.70 for wake time) than in those with fixed sleep schedules (r = 0.44) 3
• Moderate correlations exist between DLMO and sleep onset measured with polysomnography (r = 0.514) or sleep diary (r = 0.653) 4

Clinical Implications

The relationship between DLMO and sleep onset has important clinical applications:

• DLMO can be used to determine whether an individual is properly entrained to the 24-hour light/dark cycle 5
• It serves as a valuable tool for assessing phase delays or advances in circadian rhythms 5
• DLMO helps identify optimal timing for chronotherapeutic interventions such as bright light therapy or exogenous melatonin administration 5

Factors Affecting DLMO-Sleep Onset Relationship

Several factors can influence the relationship between DLMO and sleep onset:

• Chronotype (morning vs. evening preference) affects how DLMO responds to light exposure and relates to sleep timing 6
• Light exposure, particularly during sensitive evening and morning windows, can shift DLMO timing relative to sleep onset 6
• Age influences DLMO timing, with DLMO occurring later with increasing age 4

Common Pitfalls and Caveats

When interpreting DLMO in relation to sleep onset:

• The absence of detectable melatonin at the expected rise time may indicate either low melatonin synthesis or abnormal circadian phase (e.g., melatonin production occurring at another time) 1
• Medications (NSAIDs, beta-blockers, alcohol) can suppress melatonin levels and affect DLMO measurement 1
• Postural changes and exercise can increase melatonin levels, potentially confounding measurements 1
• Light exposure, even at levels lower than typical room illumination, can suppress melatonin and affect DLMO determination 1