Longitudinal Stability and Contextual Sensitivity of At-Home Salivary Dim Light Melatonin Onset (DLMO): A Four-Year N-of-1 Study

ABSTRACT At-home collected salivary Dim Light Melatonin (DLMO) assessments have demonstrated agreement with laboratory-determined DLMO estimates, but key translational gaps remain. We compiled 32 at-home salivary DLMO assessments obtained over four years from a healthy adult male (35– 40 years old) with stable sleep-wake patterns to characterize the magnitude of behavioral, environmental, and pharmacologic influences on DLMO and melatonin profile morphology at the individual level. The series included 10 assessments conducted under standardized dim light conditions to establish a baseline pattern, 21 assessments following controlled contextual manipulations (including exogenous melatonin, ambient and bright-light exposures, blue-blocking glasses, diazepam, behaviorally delayed bedtime scheduling, melatonin-rich foods, magnesium, caffeine, alcohol, late-evening anaerobic exercise), and one seasonal photoperiod comparison. Across a series of 10 baseline assessments, DLMO timing demonstrated high intra-individual stability (range: 7:13 PM–8:43 PM; SD = 28 min), and peak melatonin levels were highly consistent (M = 13.26 pg/mL, SE = 0.46 pg/mL). Within this individual, 5-day magnesium supplementation (3.6 mg/kg per day), caffeine (300 mg), alcohol (6oz of 80-proof), melatonin-rich foods, or intense anaerobic exercise during the DLMO assessment window produced negligible deviation in DLMO timing or changes in peak concentrations. In contrast, continuous bright light (∼1500 lux) during the established pre-onset interval suppressed melatonin production and obscured central circadian phase estimation, while bright light exposure after melatonin onset also produced steep declines in melatonin levels. Diazepam (0.12 mg/kg per day, over a 5-day period) delayed melatonin timing and attenuated melatonin levels. In contrast, Escitalopram (0.24 mg/kg per day, over a 60-day period) elevated baseline melatonin concentrations without obvious alteration of the underlying onset of melatonin secretion at the dosage evaluated. A behaviorally delayed sleep-wake time (i.e., 5 hours for 10 days) resulted in a corresponding delay in melatonin onset consistent with entrainment to the altered bedtime. Exogenous melatonin (0.06 mg/kg) produced supraphysiologic concentrations, which precluded interpretation of the endogenous circadian phase. These findings demonstrate that contextual influence on at-home DLMO assessment may differ substantially in effect magnitude at the individual level of analysis. Discussion focuses on the distinction between higher-impact, first-order threats and low-negligible-impact “second-order” threats to at-home DLMO measurement validity.