Estimating dim light melatonin onset time in children using delta changes in melatonin.

We aimed to establish a method for estimating dim light melatonin onset (DLMO) using mathematical slopes calculated from melatonin concentrations at three sampling points before and after sleep in children. The saliva of 30 children (mean age ± SD: 10.2 ± 1.3 years old) was collected under dim-light conditions up to six times every hour starting at 17:30 (t17), namely, 18:30 (t18), 19:30 (t19), 20:30 (t20), 21:30 (t21), 22:30 (t22), and 23:30 (t23), in the evening, and at 6:00 (t30) the following morning. We calculated SLOPEon (mathematical slope between melatonin concentrations at t18 and t20, t21 or t22), SLOPEoff (the slope between t20, t21 or t22, and t30), and ΔSLOPE, which is generated by subtracting SLOPEon from SLOPEoff. DLMO was estimated by multiple regression analysis with the leave-one-out cross-validation (LOOCV) method using SLOPEon and SLOPEoff, and ΔSLOPE. The intraclass correlation coefficient (ICC) between the estimated and measured DLMOs was used as the index of estimation accuracy. DLMOs estimated using multiple regression equations with SLOPEon and SLOPEoff yielded significant ICCs for the measured DLMOs, with the largest ICC at t20 (ICC = 0.634). Additionally, the ICC between the estimated and measured DLMOs using the equation with ΔSLOPE was significant, with a larger ICC at t20 (ICC = 0.726) than that of the equation with SLOPEon and SLOPEoff. Our results showed that DLMO could be estimated with a certain level of accuracy from salivary melatonin levels at three time points before and after sleep in children. Supplementary Information: The online version contains supplementary material available at 10.1007/s41105-023-00493-x.

The Japanese version of the reduced morningness-eveningness questionnaire.

Circadian typology, or "morningness" and "eveningness," is generally assessed using the Morningness-Eveningness Questionnaire (MEQ), a 19-item scale that could be burdensome in large-scale surveys. To overcome this, a 5-item version known as the reduced morningness-eveningness questionnaire (rMEQ), which is sensitive to the assessment of circadian typology, was developed; however, a validated Japanese version of the rMEQ is yet to be established. This study aimed to develop and validate the Japanese version of the rMEQ. Five essential items for the rMEQ were selected from existing Japanese MEQ data (N = 2,213), and the rMEQ was compiled. We conducted a confirmatory factor analysis for the psychometric properties of the rMEQ and confirmed its robust one-factor structure for evaluating morningness-eveningness (GFI = 0.984, AGFI = 0.951, CFI = 0.935, and RMSEA = 0.091). Reliability was evaluated via internal consistency of rMEQ items using Cronbach's α and McDonald's ω, and the values were 0.618 and 0.654, respectively. The rMEQ scores strongly correlated with MEQ (ρ = 0.883, p < 0.001), and classification agreement (Morning, Neither, and Evening types) between rMEQ and MEQ was 77.6% (Cramer's V = 0.643, Weighted Cohen's κ = 0.72), confirming the validity. The Japanese rMEQ may be a valuable tool for the efficient assessment of circadian typologies.

Sleep patterns in Metropolitan and Regional areas in Japan: Before and during COVID-19 social restrictions.

Sleep timing is an important output of the circadian system. The COVID-19-mandated social restrictions significantly altered commuting time and sleep duration regionally in Japan. This study aimed to elucidate sleep patterns, especially chronotype and social jetlag (SJL), due to changes in social time pressure through the social restrictions between the Metropolitan and Regional areas in Japan. As part of the Global Chrono Corona Survey 2020 (GCCS), the data were collected during social restrictions (SR), but pre-COVID-19 behaviours were also queried retrospectively. We analyzed a cohort of 729 respondents representing both the Metropolitan and the Regional areas separately for workdays and work-free days. While the areas showed no difference in SJL before SR, the differential decrease was larger in the Metropolitan area during SR, resulting in a significant difference in SJL between the areas. The outdoor light exposure before SR was 30 min longer in the Metropolitan areas than in the Regional; during SR both areas showed similarly low (below 1 h) outdoor light exposures. The variables associated with decreased SJL were the Metropolitan areas, work-from-home, a no-usage alarm clock on workdays, and chronotypes (mid-sleep time on free days corrected for sleep deficit accumulated over the workweek, MSFsc) during SR. The results suggest that relaxed social schedules, as reflected in the increased frequency of work-from-home and reduced alarm clock use, and moving towards earlier MSFsc during SR were linked to decreased SJL and were more prominent in the Metropolitan areas. This study provides insights into sleep patterns and the social time pressure markers, by comparison between residential groups in Japan.

Association between sleep state misperception and bedtime behavior in patients with chronic insomnia.

Previous studies on sleep state misperception have objectively evaluated sleep status in special environments using polysomnography. There is a paucity of data from studies that evaluated habitual sleep status in home environments. The present study aimed to investigate sleep state misperception in the home environment of patients with chronic insomnia using a lumbar-worn actigraphy to identify sleep habits associated with sleep state misperception severity. Thirty-one patients and 42 healthy volunteers were included in the insomnia and non-insomnia group, respectively. Participants recorded subjective assessments in sleep diaries, objective assessments with an actigraphy worn for 14 days, and self-assessments using questionnaires. Both groups had similar objective sleep ratings; however, insomnia group had significantly worse subjective ratings (total sleep time, wake after sleep onset, and sleep onset latency). A significant correlation was found between subjective and objective total sleep time scores in non-insomnia group but not in insomnia group. Insomnia group had earlier bedtimes, significantly longer bedtimes, and impaired daytime functioning (Sheehan Disability Scale score); additionally, they underestimated their total sleep time, particularly with earlier bedtimes and longer laying durations. Monitoring the sleep status and habits of individuals in home environments could be instrumental in identifying key points for targeted interventions on sleep hygiene and cognitive behavioral therapy for insomnia.

Development and validation of the Japanese version of the Bedtime Procrastination Scale (BPS-J).

BACKGROUND: The average sleep duration of Japanese people is shorter than that of people from other countries, and bedtime procrastination is suspected to be one of the factors contributing to this issue. This study aimed to develop and validate the Japanese version of the Bedtime Procrastination Scale (BPS-J). METHODS: The BPS-J was developed through procedures including the translation and back-translation of the scale, cognitive interviews with 100 participants who reported having experiences of being diagnosed with insufficient sleep syndrome (ISS) or receiving treatment for ISS using open-ended online questionnaires, and expert checking. To investigate the scale's validity and reliability, an online survey was conducted with daytime workers aged 20 - 65 years without a history of sleep disorders other than ISS. Half the participants were retested using the same survey after 14 days. Participants' responses to the Brief Self-Control Scale (BSCS), General Procrastination Scale (GPS), and Munich ChronoType Questionnaire (MCTQ), and data on sleep-related variables such as sleep duration on workdays and the days per week of fatigue or sleep loss, sex, and age, were collected. RESULTS: We analyzed data from 574 participants to assess scale validity. We then analyzed data from 280 participants to determine test-retest reliability. Confirmatory factor analyses revealed that the two-factor model without Item 2 was most suitable for the BPS-J, unlike other language versions. Regardless of the full-item model or the model with Item 2 eliminated, sufficient reliability and significant correlations with the BSCS, GPS, MCTQ, and sleep-related variables such as sleep duration per night on work days, days per week of feeling fatigued, and days per week of sleep loss were observed. Logistic and linear regressions showed that the relationships between the BPS-J, sleep-related variables, and MCTQ were maintained after adjusting for sex and age. CONCLUSION: The BPS-J had sufficient validity and reliability. Further, eliminating Item 2 from the original version of the BPS strengthened the ability to survey Japanese daytime workers.

Association between sleep duration and antibody acquisition after mRNA vaccination against SARS-CoV-2.

Introduction: Sleep enhances the antibody response to vaccination, but the relationship between sleep and mRNA vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is not fully understood. Methods: In this prospective observational study, we investigated the influence of sleep habits on immune acquisition induced by mRNA vaccines against SARS-CoV-2 in 48 healthy adults (BNT-162b2, n=34; mRNA-1273, n=14; female, n=30, 62.5%; male, n=18, 37.5%; median age, 39.5 years; interquartile range, 33.0-44.0 years) from June 2021 to January 2022. The study measured sleep duration using actigraphy and sleep diaries, which covered the periods of the initial and booster vaccinations. Results: Multivariable linear regression analysis showed that actigraphy-measured objective sleep duration 3 and 7 days after the booster vaccination was independently and significantly correlated with higher antibody titers (B=0.003; 95% confidence interval, 0.000-0.005; Beta=0.337; p=0.02), even after controlling for covariates, including age, sex, the type of vaccine, and reactogenicity to the vaccination. Associations between acquired antibody titer and average objective sleep duration before vaccination, and any period of subjective sleep duration measured by sleep diary were negligible. Discussion: Longer objective, but not subjective, sleep duration after booster vaccination enhances antibody response. Hence, encouraging citizens to sleep longer after mRNA vaccination, especially after a booster dose, may increase protection against SARS-CoV-2. Study registration: This study is registered at the University Hospital Medical Information Network Center (UMIN: https://www.umin.ac.jp) on July 30, 2021, #UMIN000045009.