Lauren Hartstein

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• Choubai, S., Harsh, J. R., Hartstein, L. E., Abbas, L., Wong, S. D., & LeBourgeois, M. K. (2025). Social jetlag is associated with body mass (BMI) in children aged 2-8 years: A cross-sectional analysis. Sleep Health, 11(Issue). doi:10.1016/j.sleh.2025.04.003
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  Objective: Social jetlag is associated with higher body mass index (BMI) in adults, adolescents, and older children. However, no research to date has addressed social jetlag and body mass index in early childhood. This study investigated the association between social jetlag and BMIz in children aged 2-8 years. Methods: Cross-sectional data were leveraged from 1122 children (M = 5.6 ± 1.7 years, 48.8% females) from the NIH Environmental influences on Child Health Outcomes (ECHO) study between 2016 and 2021. Sleep timing was parent-reported. Social jetlag was calculated as the absolute difference in weekend-weekday sleep midpoint. Objective measurements of children's height and weight were used to compute age- and sex-adjusted BMIz. Regression models tested the association between social jetlag and BMIz, adjusting for sociodemographic and sleep covariates. Results: After controlling for age, sex, race and ethnicity, primary caregiver education, and average nighttime sleep duration, social jetlag was positively associated with BMIz (β = 0.126, 95% CI: 0.004-0.249, p = .043). Children with ≥1-h social jetlag had higher average BMIz and had 66% higher odds of being overweight or obese (OR = 1.66, 95% CI: 1.13-2.46, p = .01), compared with children with no social jetlag. Conclusions: Social jetlag may contribute to higher BMIz in young children, similar to findings in older children, adolescents, and adults. At least 1 hour of social jetlag may increase children's odds of being overweight or obese. Future research is needed to test causality and whether reducing social jetlag can lead to healthy weight-related outcomes.
• Hartstein, L. E., Wright, K. P., Diniz Behn, C., Stowe, S. R., & LeBourgeois, M. K. (2025). The Circadian Response to Evening Light Spectra in Early Childhood: Preliminary Insights. Journal of Biological Rhythms, 40(Issue). doi:10.1177/07487304241311652
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  Although the sensitivity of the circadian system to the characteristics of light (e.g., biological timing, intensity, duration, spectrum) has been well studied in adults, data in early childhood remain limited. Utilizing a crossover, within-subjects design, we examined differences in the circadian response to evening light exposure at two different correlated color temperatures (CCT) in preschool-aged children. Healthy, good sleeping children (n = 10, 3.0-5.9 years) completed two 10-day protocols. In each protocol, after maintaining a stable sleep schedule for 7 days, a 3-day in-home dim-light circadian assessment was performed. On the first and third evenings of the in-home protocol, dim-light melatonin onset (DLMO) was assessed. On the second evening, children received a 1-h light exposure of 20 lux from either 2700 K (low CCT) or 5000 K (high CCT) (~9 and ~16 melanopic equivalent daylight illuminance (mEDI lux), respectively) centered around their habitual bedtime. Children received the remaining light condition during their second protocol, with the order counterbalanced across participants. Salivary melatonin was collected to compute melatonin suppression and circadian phase shift resulting from each experimental light condition. Melatonin suppression across the 1-h light stimulus was significantly greater during exposure to the high CCT light (M = 56.3%, SD = 19.25%) than during the low CCT light (M = 23.90%, SD = 41.06%). Both light conditions resulted in marked delays of circadian timing, but only a small difference (d = −0.25) was observed in the delay between the 5000 K (M = 35.3 min, SD = 34.3 min) and 2700 K (M = 26.7 min, SD = 15.9 min) conditions. Together, these findings add to a growing literature demonstrating high responsivity of the circadian clock to evening light exposure in early childhood and provide preliminary evidence of melatonin suppression sensitivity to differences in light spectrum in preschool-aged children.
• Reichenberger, D. A., Mathew, G. M., Brombach, R. K., Hartstein, L. E., Rodriguez, I. R., Bowles, N. P., Dzierzewski, J. M., & Hale, L. (2025). Designing sleep disruption: The digital persuasion underlying screen use and sleep. Sleep Medicine Reviews, 79(Issue). doi:10.1016/j.smrv.2024.102026
• Hartstein, L. E., Garrison, M. M., Lewin, D., Boergers, J., & Lebourgeois, M. K. (2024). Characteristics of Melatonin Use among US Children and Adolescents. JAMA Pediatrics, 178(Issue 1). doi:10.1001/jamapediatrics.2023.4749
• Hartstein, L. E., Garrison, M. M., Lewin, D., Boergers, J., Hiraki, B. K., Harsh, J. R., & LeBourgeois, M. K. (2024). Factors contributing to U.S. parents’ decisions to administer melatonin to children. Sleep Medicine, 114(Issue). doi:10.1016/j.sleep.2023.12.018
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  Objective: Pediatric melatonin use is increasingly prevalent in the U.S. despite limited research on its efficacy and long-term safety. The current study investigated factors contributing to parents’ decisions whether to give children melatonin. Methods: Parents of children 1.0–13.9 years completed an online questionnaire on children's health, sleep, and melatonin use. Parents who reported giving melatonin to their child were asked open-ended follow-up questions on why their child takes melatonin and why they stopped (if applicable). Responses were assigned to categories through thematic coding. Results: Data were analyzed on 212 children who either consumed melatonin in the past 30 days (n = 131) or took melatonin previously (n = 81). Among children who recently took melatonin, 51.1 % exhibited bedtime resistance and 46.2 % had trouble falling asleep. Parents most commonly gave children melatonin to: help them fall asleep (49.3 %), wind down before bedtime (22.7 %), facilitate changes in their sleep routine (17.5 %), and/or change their circadian rhythm (11.4 %). Parents stopped giving melatonin because their child did not need it anymore (32.0 %), experienced negative side effects (9.3 %), and/or concerns about health and safety (13.3 %). Finally, parents initiated melatonin use on their own (50.0 %), were encouraged by a friend or family member (27.4 %), and/or followed the recommendation of a health provider (48.1 %). Conclusions: Parents administered melatonin to children for a number of reasons and discontinued melatonin based on their own observations of a variety of effects. Parents frequently initiated use without the recommendation of a medical professional. Further research on indications and efficacy of melatonin and wider dissemination of guidelines are needed to help parents make informed decisions regarding children's sleep health.
• Hartstein, L. E., LeBourgeois, M. K., Durniak, M. T., & Najjar, R. P. (2024). Differences in the pupillary responses to evening light between children and adolescents. Journal of Physiological Anthropology, 43(Issue 1). doi:10.1186/s40101-024-00363-6
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  Background: In the mammalian retina, intrinsically-photosensitive retinal ganglion cells (ipRGC) detect light and integrate signals from rods and cones to drive multiple non-visual functions including circadian entrainment and the pupillary light response (PLR). Non-visual photoreception and consequently non-visual sensitivity to light may change across child development. The PLR represents a quick and reliable method for examining non-visual responses to light in children. The purpose of this study was to assess differences in the PLRs to blue and red stimuli, measured one hour prior to bedtime, between children and adolescents. Methods: Forty healthy participants (8–9 years, n = 21; 15–16 years, n = 19) completed a PLR assessment 1 h before their habitual bedtime. After a 1 h dim-light adaptation period (< 1 lx), baseline pupil diameter was measured in darkness for 30 s, followed by a 10 s exposure to 3.0 × 1013 photons/cm2/s of either red (627 nm) or blue (459 nm) light, and a 40 s recovery in darkness to assess pupillary re-dilation. Subsequently, participants underwent 7 min of dim-light re-adaptation followed by an exposure to the other light condition. Lights were counterbalanced across participants. Results: Across both age groups, maximum pupil constriction was significantly greater (p < 0.001, ηp2 = 0.48) and more sustained (p < 0.001, ηp2 = 0.41) during exposure to blue compared to red light. For adolescents, the post-illumination pupillary response (PIPR), a hallmark of melanopsin function, was larger after blue compared with red light (p = 0.02, d = 0.60). This difference was not observed in children. Across light exposures, children had larger phasic (p < 0.01, ηp2 = 0.20) and maximal (p < 0.01, ηp2 = 0.22) pupil constrictions compared to adolescents. Conclusions: Blue light elicited a greater and more sustained pupillary response than red light in children and adolescents. However, the overall amplitude of the rod/cone-driven phasic response was greater in children than in adolescents. Our findings using the PLR highlight a higher sensitivity to evening light in children compared to adolescents, and continued maturation of the human non-visual photoreception/system throughout development.
• Reichenberger, D. A., Hartstein, L. E., Mathew, G. M., Rodriguez, I. R., Dzierzewski, J. M., & Hale, L. (2024). Content contains multitudes – It's more than arousal before sleep. Sleep Medicine Reviews, 76(Issue). doi:10.1016/j.smrv.2024.101954
• Hartstein, L. E., Diniz Behn, C., Wright, K. P., Akacem, L. D., Stowe, S. R., & LeBourgeois, M. K. (2023). Evening Light Intensity and Phase Delay of the Circadian Clock in Early Childhood. Journal of Biological Rhythms, 38(Issue 1). doi:10.1177/07487304221134330
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  Late sleep timing is prevalent in early childhood and a risk factor for poor behavioral and health outcomes. Sleep timing is influenced by the phase of the circadian clock, with later circadian timing linked to delayed sleep onset in young children. Light is the strongest zeitgeber of circadian timing and, in adults, evening light produces circadian phase delay in an intensity-dependent manner. The intensity-dependent circadian phase-shifting response to evening light in children, however, is currently unknown. In the present study, 33 healthy, good-sleeping children aged 3.0 to 4.9 years (M = 4.14 years, 39% male) completed a 10-day between-subjects protocol. Following 7 days of a stable sleep schedule, an in-home dim-light circadian assessment was performed. Children remained in dim-light across 3 days (55 h), with salivary melatonin collected in regular intervals throughout each evening. Phase-shifting effects of light exposure were determined via changes in the timing of the dim-light melatonin onset (DLMO) prior to (Day 8) and following (Day 10) a light exposure stimulus. On Day 9, children were exposed to a 1 h light stimulus in the hour before their habitual bedtime. Each child was randomly assigned to one intensity between 5 and 5000 lux (4.5-3276 melanopic EDI). Across light intensities, children showed significant circadian phase delays, with an average phase delay of 56.1 min (SD = 33.6 min), and large inter-individual variability. No relationship between light intensity and magnitude of the phase shift was observed. However, a greater percentage of melatonin suppression during the light exposure was associated with a greater phase delay (r = −0.73, p < 0.01). These findings demonstrate that some young children may be highly sensitive to light exposure in the hour before bedtime and suggest that the home lighting environment and its impact on circadian timing should be considered a possible contributor to behavioral sleep difficulties.
• Hartstein, L. E., Wong, S. D., Abbas, L., Choubai, S., Wilson, J. N., Jablin, T., & LeBourgeois, M. K. (2023). Creating the Cave: Conducting Circadian Science in Early Childhood. Clocks and Sleep, 5(Issue 1). doi:10.3390/clockssleep5010009
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  In humans, physiological outputs of the body’s internal clock (i.e., saliva, serum, and temperature) can be collected to quantify the timing of the circadian system. In-lab assessment of salivary melatonin in a dimly lit environment is a common approach for adolescents and adults; however, the reliable measurement of melatonin onset in toddlers and preschoolers requires a modification of laboratory methods. For > 15 years, we have successfully collected data from ~250 in-home dim light melatonin onset (DLMO) assessments of children aged 2–5 years. Although in-home studies of circadian physiology may introduce a host of challenges and may increase the risk of incomplete data (e.g., accidental light exposure), in-home studies afford more comfort (e.g., less arousal in children) and flexibility for families. Here, we provide effective tools and strategies to assess children’s DLMO, a reliable marker of circadian timing, through a rigorous in-home protocol. We first describe our basic approach, including the study protocol, collection of actigraphy data, and strategies for training child participants to complete procedures. Next, we detail how to convert the home into a “cave”, or dim-light environment, and present guidelines for timing the salivary data collection. Lastly, we provide helpful tips to increase participants’ compliance based upon behavioral and developmental science tenets.
• Hartstein, L. E., Wright, K. P., Akacem, L. D., Diniz Behn, C., & LeBourgeois, M. K. (2023). Evidence of circalunar rhythmicity in young children's evening melatonin levels. Journal of Sleep Research, 32(Issue 2). doi:10.1111/jsr.13635
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  In adults, recent evidence demonstrates that sleep and circadian physiology change across lunar phases, including findings that endogenous melatonin levels are lower near the full moon compared to the new moon. Here, we extend these results to early childhood by examining circalunar fluctuations in children's evening melatonin levels. We analysed extant data on young children's circadian rhythms (n = 46, aged 3.0–5.9 years, 59% female). After following a strict sleep schedule for 5–7 days, children completed an in-home, dim-light circadian assessment (
• Reynolds, A. M., Spaeth, A. M., Hale, L., Williamson, A. A., LeBourgeois, M. K., Wong, S. D., Hartstein, L. E., Levenson, J. C., Kwon, M., Hart, C. N., Greer, A., Richardson, C. E., Gradisar, M., Clementi, M. A., Simon, S. L., Reuter-Yuill, L. M., Picchietti, D. L., Wild, S., Tarokh, L., , Sexton-Radek, K., et al. (2023). Pediatric sleep: current knowledge, gaps, and opportunities for the future. Sleep, 46(Issue 7). doi:10.1093/sleep/zsad060
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  This White Paper addresses the current gaps in knowledge, as well as opportunities for future studies in pediatric sleep. The Sleep Research Society’s Pipeline Development Committee assembled a panel of experts tasked to provide information to those interested in learning more about the field of pediatric sleep, including trainees. We cover the scope of pediatric sleep, including epidemiological studies and the development of sleep and circadian rhythms in early childhood and adolescence. Additionally, we discuss current knowledge of insufficient sleep and circadian disruption, addressing the neuropsychological impact (affective functioning) and cardiometabolic consequences. A significant portion of this White Paper explores pediatric sleep disorders (including circadian rhythm disorders, insomnia, restless leg and periodic limb movement disorder, narcolepsy, and sleep apnea), as well as sleep and neurodevelopment disorders (e.g. autism and attention deficit hyperactivity disorder). Finally, we end with a discussion on sleep and public health policy. Although we have made strides in our knowledge of pediatric sleep, it is imperative that we address the gaps to the best of our knowledge and the pitfalls of our methodologies. For example, more work needs to be done to assess pediatric sleep using objective methodologies (i.e. actigraphy and polysomnography), to explore sleep disparities, to improve accessibility to evidence-based treatments, and to identify potential risks and protective markers of disorders in children. Expanding trainee exposure to pediatric sleep and elucidating future directions for study will significantly improve the future of the field.
• Hartstein, L. E., Behn, C. D., Akacem, L. D., Stack, N., Wright, K. P., & LeBourgeois, M. K. (2022). High sensitivity of melatonin suppression response to evening light in preschool-aged children. Journal of Pineal Research, 72(Issue 2). doi:10.1111/jpi.12780
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  Light at night in adults suppresses melatonin in a nonlinear intensity-dependent manner. In children, bright light of a single intensity before bedtime has a robust melatonin suppressing effect. To our knowledge, whether evening light of different intensities is related to melatonin suppression in young children is unknown. Healthy, good-sleeping children (n = 36; 3.0–4.9 years; 39% male) maintained a stable sleep schedule for 7 days followed by a 29.5-h in-home dim-light circadian assessment (~1.5 lux). On the final night of the protocol, children received a 1-h light exposure (randomized to one of 15 light levels, ranging 5–5000 lux, with ≥2 participants assigned to each light level) in the hour before habitual bedtime. Salivary melatonin was measured to calculate the magnitude of melatonin suppression during light exposure compared with baseline levels from the previous evening, as well as the degree of melatonin recovery 50 min after the end of light exposure. Melatonin levels were suppressed between 69.4% and 98.7% (M = 85.4 ± 7.2%) during light exposure across the full range of intensities examined. Overall, we did not observe a light intensity-dependent melatonin suppression response; however, children exposed to the lowest quartile of light intensities (5–40 lux) had an average melatonin suppression (77.5 ± 7.0%) which was significantly lower than that observed at each of the three higher quartiles of light intensities (86.4 ± 5.6%, 89.2 ± 6.3%, and 87.1 ± 5.0%, respectively). We further found that melatonin levels remained below 50% baseline for at least 50 min after the end of light exposure for the majority (62%) of participants, and recovery was not influenced by light intensity. These findings indicate that preschool-aged children are highly sensitive to light exposure in the hour before bedtime and suggest the lighting environment may play a crucial role in the development and the maintenance of behavioral sleep problems through impacts on the circadian timing system.
• Blackwell, C. K., Hartstein, L. E., Elliott, A. J., Forrest, C. B., Ganiban, J., Hunt, K. J., Camargo, C. A., & LeBourgeois, M. K. (2020). Better sleep, better life? How sleep quality influences children’s life satisfaction. Quality of Life Research, 29(Issue 9). doi:10.1007/s11136-020-02491-9
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  Purpose: To assess the association between children’s sleep quality and life satisfaction; and to evaluate the underlying mechanisms of this relationship. Methods: Three pediatric cohorts in the National Institutes of Health (NIH) Environmental influences on Child Health (ECHO) Research Program administered Patient-Reported Outcome Measurement Information System (PROMIS®) parent-proxy measures to caregivers (n = 1111) who reported on their 5- to 9-year-old children’s (n = 1251) sleep quality, psychological stress, general health, and life satisfaction; extant sociodemographic data were harmonized across cohorts. Bootstrapped path modeling of individual patient data meta-analysis was used to determine whether and to what extent stress and general health mediate the relationship between children’s sleep quality and life satisfaction. Results: Nonparametric bootstrapped path analyses with 1000 replications suggested children’s sleep quality was associated with lower levels of stress and better general health, which, in turn, predicted higher levels of life satisfaction. Family environmental factors (i.e., income and maternal mental health) moderated these relationships. Conclusion: Children who sleep well have happier lives than those with more disturbed sleep. Given the modifiable nature of children’s sleep quality, this study offers evidence to inform future interventional studies on specific mechanisms to improve children’s well-being.
• Hartstein, L. E., Tuzikas, A., & Karlicek, R. F. (2020). The Impact of Dynamic Changes in Light Spectral Power Distribution on Cognitive Performance and Wellbeing. LEUKOS - Journal of Illuminating Engineering Society of North America, 16(Issue 4). doi:10.1080/15502724.2019.1693896
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  The spectral power distribution (SPD) of the indoor lighting environment can improve cognitive performance, as well as positively impact occupant wellbeing. Advances in solid-state lighting now allow the SPD of indoor light sources to change temporally to better match the dynamic quality of the natural environment. The present study sought to explore how rapid, dynamic changes in light SPD can impact cognitive performance and comfort compared to traditional, static indoor light fixtures. In this study, undergraduate students completed tasks measuring attention and processing speed, as well as questionnaires of sleepiness, emotion, and headache and eyestrain under traditional static lighting or a dynamic lighting condition consisting of fluctuations in light correlated color temperature (CCT) and constant illuminance. In Experiment 1, consistent, cyclical changes in CCT (4700–5300 K in a triangular wave pattern at a frequency of 0.03 Hz) were found to negatively impact participants’ processing speed and reported ability to focus. However, these impairments were accompanied by a decrease in negative affect. In contrast, stochastic changes in CCT used in Experiment 2 (4700–5300K in semi-random changes at a frequency of 0.03, 0.07, or 0.10 Hz) produced no measured effects on participant task performance, alertness, mood, or comfort, suggesting that a degree of unpredictability in the frequency of changes in light CCT may be less disruptive to occupant performance and focus than regular, cyclical changes. The preliminary findings from this small-scale study highlight the need for further research into how changes in the lighting environment might be beneficial or detrimental to occupant performance and comfort.
• Hartstein, L. E., & Berthier, N. E. (2018). Transition to success on the model room task: the importance of improvements in working memory. Developmental Science, 21(Issue 2). doi:10.1111/desc.12538
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  Previous work has shown that children under age 3 often perform very poorly on the model room task, in which they are asked to find a hidden toy based on its location in a scale model. One prominent theory for their failure is that they lack the ability to understand the model as both a physical object and as a symbolic representation of the larger room. A hypothesized additional component is that they need to overcome weak, competing representations of where the object was on a previous trial, and where it is in the present trial, in order to succeed in their search. Children aged 33–39 months were tested on the model room task, as well as on measures of cognitive inhibitory control, cognitive flexibility, and working memory. Results showed that performance on the model room task was not predicted by measures of inhibitory control or cognitive flexibility, but was predicted by performance on the Delayed Recognition Span Test (DRST), a measure of working memory. These findings lend support to the theory of competing representations and demonstrate the necessity of updating and maintaining strong representations in working memory to succeed in the search task.
• Hartstein, L. E., Durniak, M. T., Karlicek, R. F., & Berthier, N. E. (2018). A comparison of the effects of correlated colour temperature and gender on cognitive task performance. Lighting Research and Technology, 50(Issue 7). doi:10.1177/1477153517721728
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  Higher correlated colour temperature ambient lighting, which contains more blue light, has been reported to improve performance on a variety of cognitive tasks. The current investigation compared performance of adults on what/where task switching, go/no-go, and mental rotation tasks when the experimental room was lit by 3500 K standard florescent and 5000 K LED lighting. Results showed that, under higher correlated colour temperature illumination, females (but not males) decreased reaction time by approximately 10% on the task switching task, that males (but not females) showed a reaction time decrease on the go/no-go tasks, and that no effect was observed on the mental rotation task. Our results suggest that higher correlated colour temperature illumination improves reaction time performance on certain attention/executive function tasks, but that that improvement is gender specific.
• Hartstein, L. E., LeBourgeois, M. K., & Berthier, N. E. (2018). Light correlated color temperature and task switching performance in preschool-age children: Preliminary insights. PLoS ONE, 13(Issue 8). doi:10.1371/journal.pone.0202973
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  Data from a growing number of experimental studies show that exposure to higher correlated color temperature (CCT) ambient light, containing more blue light, can positively impact alertness and cognitive performance in older children and adults. To date, few if any studies have examined whether light exposure influences cognitive task performance in preschool-age children, who are in the midst of rapid developmental changes in attention and executive function skills. In this study, healthy children aged 4.5–5.5 years (n = 20; 11 females) completed measures of sustained attention and task switching twice while being exposed to LED light set to either 3500K (a lower CCT) or 5000K (a higher CCT). A control group (n = 18; 10 females) completed the tasks twice under only the 3500K lighting condition. Although the lighting condition did not impact performance on the sustained attention task, exposure to the higher CCT light lead to greater improvement in preschool-age children’s task switching performance (F(1,36) = 4.41, p = 0.04). Children in the control group showed a 6.5% increase in task switching accuracy between time points, whereas those in the experimental group improved by 15.2%. Our primary finding–that exposure to light at a higher correlated color temperature leads to greater improvement in task switching performance–indicates that the relationship between the spectral power distribution of light and executive function abilities is present early in cognitive development. These data have implications for designing learning environments and suggest that light may be an important contextual factor in the lives of young children in both the home and the classroom.

Presentations

• Hartstein, L. (2025).

  Circadian responses to light in early childhood.

  . Research Roundtable & Symposium, Diversity in the Circadian, Neuroendocrine and Neurobehavioral Effects of Light in Humans..
• Hartstein, L. (2025).

  Natural and behavioral strategies to support children’s sleep.

  . Sleep 101 Symposium.