Yuki Nishimura

Prior light exposure can influence the magnitude of melatonin suppression in response to evening light, even within the same individual. We examined whether light-induced melatonin suppression in school-aged children differed before and during a camp with approximately two weeks of exposure to a natural light-dark cycle. We also explored interindividual variation in melatonin suppression and its associations with circadian phase, habitual sleep timing, and daytime light exposure. Twenty-one healthy children aged 9—14 years underwent evening light experiments at the start of camp (Pre-camp session) and approximately two weeks later (Camp session). Melatonin suppression was calculated by comparing the area under the melatonin concentration curve between the evening light condition (200 ± 30 lx, 5000 K) and the dim light condition (< 30 lx, incandescent lamps), with integration starting at dim light melatonin onset (DLMO). We assessed sleep habits from 14-day sleep diaries before camping and measured wrist-level illuminance during camping. We examined associations using Spearman correlations and compared Pre-camp and Camp melatonin suppression using a paired t-test. Melatonin suppression did not differ significantly between Pre-camp and Camp sessions (p = 0.21). Greater suppression in the Pre-camp session was associated with later DLMO (rho = 0.49, p = 0.028), but not with habitual sleep variables. In the Camp session, higher same-day geometric mean illuminance was associated with lower suppression (n = 15; rho = −0.58, p = 0.024), whereas 7-day light-exposure metrics were not. Mean melatonin suppression did not significantly change across the camping period. Meanwhile, children showed large interindividual variation in melatonin suppression, and circadian phase and recent daytime light exposure are candidate correlates of this variation in the responsiveness to the evening light.

Objectives: This study examined the association between work start time (within-person and between-person effects) and work start time irregularity with objective sleep and health-related outcomes. Methods: A 10-day field study was conducted with 143 employees. Daily work start times, blood pressure (BP), subjective state, brief psychomotor vigilance test, and actigraphic sleep variables were assessed. Work start time was decomposed into within- and between-person components using person-mean centering. Work start time irregularities were quantified using the interquartile range of work start times during the observation period. Linear mixed models were used. Results: Earlier-than-usual work start times (within-person level) were significantly associated with shorter actigraphic total sleep time (TST; β = 6.50), earlier lights-off time (β = 0.10), bed-out times (β = 0.24), higher systolic (β = −0.80) and diastolic (β = −0.74) BP after waking. In contrast, earlier average work start times (between-person level) were significantly associated with earlier lights-off time (β = 0.63) and bed-out times (β = 0.76), but not TST and BP. Greater work start-time irregularity was significantly associated with higher systolic and diastolic BP before bedtime (β = 2.38 and β = 1.92) and after waking (β = 2.77 and β = 2.04). Conclusions: Earlier work start times were associated with sleep and health-related outcomes, although the patterns differed between within- and between-person levels. Work start time irregularity was associated with elevated pre-bedtime and post-waking BP; however, associations with sleep and other outcomes were limited. These findings underscore the importance of distinguishing within- and between-person effects.

Objectives This study examined the association between daily long working hours (LWHs) and diverse health-related outcomes, using objective and subjective measures. It further evaluated the specific durations of daily LWHs that may be considered inappropriate in cases with adverse health effects. Methods 98 employees participated in a 10-day observational study. Participants self-reported their daily working hours, subjective states and performed the measurement of blood pressure (BP) and psychomotor vigilance test (PVT) immediately on waking and before bedtime. Objective sleep was recorded nightly using actigraphy. Linear mixed model (LMM) analysis was performed. Results LWHs were significantly associated with higher systolic BP (β=0.65), greater fatigue (β=1.79) before bedtime, shorter total sleep time (TST; β=−0.09) and higher systolic BP (β=0.76) on waking (all p13 hours significantly reduced TST compared to working ≤9 hours. Sleeping Conclusions Daily LWHs and consequent reductions in sleep duration were associated with adverse outcomes. These findings underscore the importance of daily management of work hours and adequate sleep duration to prevent excessive workload and promote recovery from occupational demands.

Here, we examine the effectiveness of a participatory artificial intelligence (AI)‐driven shift‐scheduling mobile application (which reflects the local improvement needs in shift scheduling) in improving the sleep quality of shift‐working geriatric caregivers. Thirty‐five shift‐working geriatric caregivers participated in this 4‐month cross‐over interventional study. Half of the participants in the first 2 months followed the intervention schedule created by the AI‐driven shift‐scheduling mobile application, while the remaining participants followed the manually created control schedule. The improvement needs in shift scheduling, derived from occupational‐fatigue counselling, were as follows: avoiding backward rotating shifts, reducing consecutive shifts, extending shift intervals and ensuring a day‐off after a night shift. Sleep phases were evaluated using a ring‐type sleep tracker. The effectiveness of the intervention was examined using three‐way multilevel analyses (condition × shift × time). Deep sleep (N3) and rapid eye movement sleep were significantly more pronounced in the intervention condition compared with the control condition ( p = 0.016, p = 0.046, respectively). However, no significant differences were detected for other outcomes. Moreover, we examined how shift combinations affected sleep outcomes. As a result, two consecutive late shifts and backward rotating shifts significantly deteriorated sleep quality and length (all p < 0.05). Our findings suggest that the shift‐scheduling app reduced the backward shift rotations, resulting in significantly better sleep outcomes than from manual schedule creation. However, the magnitude of reduction in backward rotating shifts was not so remarkable. Therefore, the positive outcomes can also be attributed to enhanced employees' working time control by reflecting the local improvement needs. Trial Registration: UMIN Clinical Trials Registry: UMIN000048495

The Reduced Morningness-Eveningness Questionnaire (rMEQ), a five-item version of the 19-item MEQ, is a practical tool for assessing circadian typology or "morningness" and "eveningness" preference. Although we previously validated the Japanese version of rMEQ with MEQ, external validation against an established standard was lacking. This study aimed to additionally validate the Japanese rMEQ in young adults by assessing the dim light melatonin onset (DLMO), a marker of circadian phase, and subjective/objective sleep-wake habits. Twenty healthy young adults (mean age: 23.0 ± 1.9 years) participated in this study and were assessed the circadian typology by rMEQ and MEQ. The sleep-wake habits were measured by sleep diary, actigraphy and the Pittsburgh Sleep Quality Index (PSQI). Salivary melatonin samples were collected to determine DLMO. Results showed significant correlations between rMEQ scores and DLMO, as well as sleep variables based on sleep diary, actigraphy and PSQI. Correlations between rMEQ scores and these variables were consistently stronger than those for MEQ. These findings highlight the validity of the Japanese rMEQ and that the rMEQ more accurately reflects circadian typology and internal circadian phases compared to MEQ, at least in Japanese young adults. The Japanese rMEQ could be a valuable tool for efficiently assessing circadian typologies in Japanese young adults.

In modern society, many workers struggle with sleep deprivation due to their work schedules and excessive workloads. Accurate self-awareness and self-monitoring abilities are crucial for workers to adopt risk-coping strategies and protective behaviors when fatigued. The current study examined the relationship between chronotypes and self-monitoring performance during 24 h of sleep deprivation. The study involved 26 male adults in a two-night experiment, and participants' diurnal preferences were evaluated using the Morningness-Eveningness Questionnaire (MEQ). Self-monitoring performance was calculated by comparing actual task performance with self-rated predicted or post-estimated performance in the psychomotor vigilance task (PVT) and Digit Symbol Substitution Task (DSST). The study found that task and self-monitoring performances in the PVT and DSST were maintained until around 4:00 h, after which they began to deteriorate. Individuals with a higher MEQ score, indicating a stronger tendency towards a morning type, showed inaccurate self-monitoring, particularly in the final quarter of the sleep deprivation experiment, due to overly optimistic predictions. However, only prediction accuracy and not post-estimation showed this correlation. This study highlights the importance of considering an individual's chronotype in workplace management, particularly in workplaces with irregular work timings, rotating shifts, and long working hours, to ensure better occupational safety.

Traditional paper-and-pencil methods have limitations for data collection in occupational health research. Here, we introduce a new web-based version (Fatigue checker web-ver.) of an application designed to better facilitate survey management and communication with participants. The application operates on mobile web browsers and integrates with LINE, Japan's most popular messaging app, and contains customizable forms, psychological tasks such as the Psychomotor Vigilance Task (PVT), Flanker Task, and n-back Task. Daily schedule acquisition is achieved via a dedicated user interface. Cross-correlation analysis showed fair synchronization between the app and gold-standard PVT equipment, indicating the app's reliability in measuring reaction times. Specifically, the analysis revealed significant cross-correlation for mean reaction time, median reaction time, mean reciprocal reaction time, and number of lapses, which indicates that the app can reliably measure fatigue and alertness levels. Since its release, the app has been successfully employed collecting high-quality data in six projects involving 571 participants. Despite minor issues, the app significantly improves the efficiency and accuracy of remote surveys, offering valuable insights into workers' health and safety. It also enables occupational health and safety specialists to monitor workers and workplaces from a broader perspective than traditional methods. The public version of the app also enables every worker to monitor their own occupational health and safety status. Insights from repeated self-checking of fatigue will promote better working conditions and environments.

We examined cardiovascular responses during driving and investigated the effects of different break patterns on these responses. Forty-seven males in their 40s and 50s participated, and the protocol included three driving sets with four break patterns. One driving set consisted of 1 hour of city driving and 1 hour of highway driving. The four break patterns were a 30-min lunch break (short/one: SO, n=12), a 60-minute lunch break (long/one: LO, n=12), a 10-min break and a 50-min lunch break (long/two: LT, n=12), and a 10-min break and a 20-min lunch break (short/two: ST, n=11). The results showed that the lunch break was significantly effective in moderating diastolic blood pressure, mean arterial pressure and heart rate for all conditions, but the long-break conditions (LO and LT) were also effective in moderating cardiac output and stroke volume. Additionally, for the same total break length, one longer break was more effective in moderating cardiovascular and subjective burden than two shorter breaks. The results of this study suggest that it is important for drivers to take a lunch break, especially a long break around an hour, to reduce cardiovascular and subjective burden during their shift.

Background: Given that nighttime sleep has more recuperative power than daytime sleep, ensuring the former is important to recovery from work, especially for shift-working nurses. In this 1-month sleep log study, we preliminarily examined how the number of monthly nighttime-sleep opportunities relates to fatigue-related outcomes among shift-working nurses. Methods: 526 nurses were required to record their daily sleep duration immediately after waking from sleep for 1 month. We analysed the associations among the four sleep groups (ie, ≤ 12, 13–19, 20–24 and≥24 nighttime-sleep opportunities per month) and fatigue-related outcomes. A one-way analysis of covariance or generalised linear mixed model (factor: sleep group) was conducted using R (version 4.2.2.) to test the association. Results: Significant differences among the four sleep groups were obtained using the excessive fatigue symptom inventory (EFSI), Pittsburgh sleep quality index (PSQI) and the numbers of near-miss incidents. Moreover, significant linear trends were observed in the EFSI and PSQI scores. Conclusions: Shift-working nurses who experienced 12 or fewer monthly nighttime-sleep opportunities showed worse fatigue-related outcomes than those who had sufficient monthly nighttime-sleep opportunities. Therefore, more attention should be paid to ensuring monthly nighttime-sleep opportunities when creating a shift schedule.