Jul 2026· Journal of Biological Rhythms· pp. 7487304261469609 - 7487304261469609· 0 citations· 32 references
Medicine
TL;DR
Although evening melatonin profiles were consistently well-defined, permitting reliable calculations of DLMO across all participants, morning melatonin patterns were often irregular in young children, suggesting DLMOff could be a reliable marker of circadian phase.
Abstract
Circadian rhythms have been shown to regulate sleep-wake timing across the lifespan, yet many questions remain about early childhood circadian physiology. Understanding dim light melatonin onset (DLMO) and offset (DLMOff), established markers of circadian phase, is essential for characterizing circadian rhythms in early childhood. We examined the distribution of salivary DLMO and DLMOff and their relationship with actigraphic sleep timing across 20 healthy preschoolers (M = 4.31 ± 0.34 years, 45% female). After maintaining a consistent sleep schedule for seven days, children completed an in-home circadian assessment. Children were awoken 1.5 h before habitual wake time and saliva samples were collected in 20–30 min intervals throughout the morning to determine DLMOff, then in the evening until 50 min past habitual bedtime to assess DLMO. A 4 pg/ml threshold was used to calculate each phase marker. DLMO ranged from 17:22 to 20:40 (M = 18:55 ± 0:54) and was positively associated with bedtime, sleep onset, and midsleep. In contrast, morning melatonin levels were highly variable, allowing DLMOff calculation in only eight participants. Within this small subsample, later DLMOff was associated with later chronotype (r = 0.81), sleep offset (r = 0.84), and midsleep (r = 0.80). Across the full sample, interpolated melatonin levels at habitual wake remained ≥ 4 pg/ml for 45% of children, a pattern broadly consistent with findings in adults, in which a majority of participants exhibit DLMOff after habitual wake time. These findings indicate that although evening melatonin profiles were consistently well-defined, permitting reliable calculations of DLMO across all participants, morning melatonin patterns were often irregular in young children. When able to be calculated, DLMOff showed strong associations with sleep timing, suggesting it could be a reliable marker of circadian phase. However, high variability and fluctuating morning melatonin patterns make DLMOff difficult to determine in many preschool-aged children.
Studies suggest that pre-bedtime screen exposure disrupts the circadian rhythm by suppressing melatonin release in the pineal gland. This study investigates melatonin suppression in toddlers after screen exposure in the home environment. We hypothesized that viewing a video as opposed to viewing a picture book before bedtime would suppress melatonin release and disrupt subsequent sleep.
Thirty-two toddlers aged 15 to 24 months participated in a within-subject design. On 2 consecutive evenings, caregivers exposed their toddler for 15 minutes to either a video on a touchscreen with the blue light filter deactivated or to a picture book, starting 45 minutes pre-bedtime. To determine melatonin concentration, caregivers collected 1 saliva sample before exposure (baseline) and 2 saliva samples 5 minutes (post_1) and 20 minutes (post_2) after exposure. Toddlers’ sleep–wake patterns were monitored using actigraphy.
Multilevel models revealed that salivary melatonin increased from baseline to post_2 irrespective of touchscreen or picture book exposure. Changes in melatonin concentration from baseline to post-exposure measurement and sleep behavior did not differ as a function of exposure condition. Sleep behavior was unrelated to melatonin suppression scores.
Contrary to expectations, our results suggest that viewing a 15-minute video on a touchscreen within an hour of bedtime is insufficient to suppress evening melatonin release and disrupt sleep under these experimental conditions in German toddlers. More studies with toddlers under naturalistic conditions are needed to understand the relevance of screen light-induced melatonin suppression as a mechanism to explain relationships between screen exposure and sleep health.
Unknown authors· Pediatrics Open Science· 0 citations
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 (38 to 42 years) 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 to 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.
C. Schwartz, S. Granger, B. M. Aldrich et al.· medRxiv· 0 citations
Chronotype describes differences in the timing of daily rhythms, regulated by the circadian system. These patterns are classified as morning or evening chronotypes. Studies show increased impulsivity, poorer health behaviors, and greater cardiometabolic risk among evening chronotypes. However, few studies evaluate these effects relative to circadian biomarkers. Additionally, time of day may impact how chronotype affects behaviors. Participants completed an eating in the absence of hunger task during morning and evening sessions. Participants were served oatmeal, then given access to snack foods. Calories consumed from each snack type was the primary outcome. Participants fasted for ≥8 h before a 9 AM morning task. For the evening task, participants fasted for 2 h and completed an 8 PM task. Dim light melatonin onset (DLMO) was measured the day following the morning task. Covariate-adjusted models evaluated differences in caloric intake across food types and sessions, and tested associations between caloric intake and DLMO. 113 participants completed the protocol (57 female; age: M = 35.6, SD = 9.87). Significant time-of-day effects were observed, with lower intake of bland (B = -5.67, p < 0.001) and salty foods (B = -15.53, p = 0.015) in the evening. Order effects showed greater intake during the second administration for total calories and all categories (ps < 0.01). Later DLMO was linked to greater appetite ratings. These finding suggest that those with later circadian timing may have greater hedonic interest in food. Future research should explore interactions between chronotype, circadian timing, and environmental factors shaping eating behaviors.
Carson Hernandez, Steven E. Carlson, Bradley Appelhans et al.· Eating Behaviors· 0 citations
It is demonstrated that endurance exercise performance is enhanced in the evening compared with the morning and suggested that behavioural markers of circadian phenotype are associated with the magnitude of diurnal variation in performance.
A. Singh, Sanjida Ahmed, S. Hesketh· European Journal of Applied...· 0 citations
Introduction: Binge eating disorder (BED) exhibits features consistent with circadian system dysregulation. This two-phase study mechanistically examined BED chronobiology. We hypothesized that dim light melatonin onset (DLMO; circadian phase) is delayed in BED and associated with illness characteristics, and be modifiable via a chronobiotic intervention. Methods: Phase 1 (P1) was a 2-week observational study comparing adults with obesity with BED (n = 43) and without BED (controls, n = 41). Phase 2 (P2) was a 4-week double-blind, randomized, controlled pilot trial in BED (NCT04724668). Participants received morning bright light (BLT; 10,000 lx) plus individually timed exogenous melatonin (3 mg) administration (BLT+ITEMA, n = 13) or sham red light (50 lx) plus placebo (n = 10). Primary outcomes were baseline DLMO differences (P1) and DLMO change (P2). Secondary/exploratory measures included wrist actigraphy and clinical features. ANCOVA, correlation, and Bayesian methods were used for statistical analysis. Results: In P1, DLMO did not differ between groups, but later DLMO correlated with greater BED severity. BED participants showed lower 24-hour locomotor amplitude and MESOR (both, posterior probability [pp] = 1), poorer diet quality, higher night eating and leptin levels (all p < 0.05). In P2, DLMO change did not differ between groups. Compared to sham+placebo, BLT+ITEMA participants had smaller reductions in peak activity (pp = 0.97) and amplitude (pp = 0.87), plus increased dietary restraint and LcN-3 fatty acids (both p < 0.05). Later baseline DLMO correlated with greater phase advance and binge eating reduction (both p < 0.05). The intervention was well tolerated. Conclusions: A later circadian phase correlated with greater BED severity, and dampened actigraphy rhythms, both support circadian disruption in BED. The mechanistic intervention is feasible and warrants refinement.
Francisco Romo-Nava, Helen J. Burgess, Thomas Blom et al.· Research Square· 0 citations
Artificial dim light at night (dLAN) depresses nocturnal melatonin peak, along with disruption in sleep and metabolism. This study asked whether exogenous melatonin administration could reverse the effects of dim light at night on sleep and metabolism in a diurnal songbird. To answer this, three groups of zebra finches (Taeniopygia guttata) of both sexes (n=6/group/sex) hatched and raised in our indoor aviary were used. While a group remained on the dark night (LD control; 12L:12D, L=150 lux: D=0 lux), as before, to the other two groups the 12-h dark night was replaced with 5-lux (equivalent to 0.048 W/m²) dim light (12L:12dLAN; dLAN). Half an hour before dark onset, consecutively for the next 11 days, the birds of a dLAN group received subcutaneous injections of melatonin (10 µg/ 100 µl vehicle), while those of the other dLAN and LD groups (controls) received 100 µl vehicle alone. Exogenous melatonin mitigated dLAN-induced disruptive effects on both nocturnal sleep and metabolism. As compared to LD and vehicle-treated controls, melatonin-treated birds showed a significantly reduced nocturnal sleep frequency (fewer awakenings) and longer sleep bout as well as reduced night-time feeding and body fattening, and restoration of normal hepatic expression of genes associated with glucose and lipid metabolism. In particular, the elevated melatonin levels prevented the midnight increase in g6pc, irs1, fasn, star and egr1, and augmented the sirt1 mRNA levels under the dLAN environment. These results suggest that nocturnal melatonin levels are a crucial component of the regulatory pathways underlying nocturnal sleep and metabolism, independent of sex, in a diurnal songbird species.
Amaan Buniyaadi, Ashwani Kumar, S. K. Bhardwaj et al.· Journal of Experimental Biol...· 0 citations
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