著者
Akihito SHIMAZU Ko MATSUDAIRA Jan DE JONGE Naoya TOSAKA Kazuhiro WATANABE Masaya TAKAHASHI
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.54, no.3, pp.282-292, 2016-05-31 (Released:2016-06-10)
参考文献数
54
被引用文献数
32 35

This study examined whether a higher level of psychological detachment during non-work time is associated with better employee mental health (Hypothesis 1), and examined whether psychological detachment has a curvilinear relation (inverted U-shaped pattern) with work engagement (Hypothesis 2). A large cross-sectional Internet survey was conducted among registered monitors of an Internet survey company in Japan. The questionnaire included scales for psychological detachment, employee mental health, and work engagement as well as for job characteristics and demographic variables as potential confounders. The hypothesized model was tested with moderated structural equation modeling techniques among 2,234 respondents working in the tertiary industries with regular employment. Results showed that psychological detachment had curvilinear relations with mental health as well as with work engagement. Mental health improved when psychological detachment increased from a low to higher levels but did not benefit any further from extremely high levels of psychological detachment. Work engagement showed the highest level at an intermediate level of detachment (inverted U-shaped pattern). Although high psychological detachment may enhance employee mental health, moderate levels of psychological detachment are most beneficial for his or her work engagement.
著者
Kayoko URAKAWA Kazuhito YOKOYAMA
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.47, no.5, pp.503-508, 2009 (Released:2009-10-15)
参考文献数
29
被引用文献数
20 20

To examine if sense of coherence (SOC) can reduce the adverse effects of job stress on mental health status, self-administered questionnaires were distributed among 740 workers in a manufacturing industry. The questionnaire contained SOC, Job Content Questionnaire (JCQ), and General Health Questionnaire (GHQ-12). Complete answers were recovered from 466 workers (62.8%), consisting of 387 males and 79 females, with ages of 45.1±12.0 yr, and used for the analysis. The logistic regression analysis revealed the followings: Both for males and females, high GHQ was significantly associated with scores on SOC and JCQ job demand subscale, i.e. the mental health status was adversely related to job demand whereas it was positively associated with SOC. Similarly, the mental health status was affected adversely by managerial work in males, whereas was positively by co-workers support in females. Thus, high SOC enables workers to cope with their job demand, which is a potent job stressor, indicating that SOC is an important factor determining their coping ability to job stress for both genders. Male managerial employees may cope with their strong job stress because of high SOC, protecting their mental health status. Social support seems also significant for prevention of mental well-being of female workers from work-related stressors.
著者
Shuhei IZAWA Nanako NAKAMURA-TAIRA Chihiro MORIISHI Toru YOSHIKAWA Rie AKAMATSU Hiroki IKEDA Tomohide KUBO
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
pp.2023-0068, (Released:2023-09-15)

Mental health problems are prevalent among the working population and must be resolved. We conducted a web-based large-scale study of workers, including a baseline survey and two follow-up surveys, to investigate the associations between self-care behaviors in daily life (e.g., stress coping, sleep, diet, and exercise), work environment improvements, and mental health among Japanese employees from various industries. In this protocol, we demonstrate the study design and demographic data of the participants in the baseline survey. Invitations to participate in this study were sent to 421,825 internet monitor registrants in February 2022. Overall, 20,000 registrants who met the inclusion criteria participated in the survey. There were large variations in occupations and working styles (e.g., physical work, night work, and teleworking) among the participants, and we also found significant differences between male and female participants in the demographic data. An overview of the survey data suggests that the demographic characteristics of the participants in this study are comparable to those reported in previous studies on Japanese employees. We plan to use these survey data in the future to examine the associations of daily lifestyles and work environments with the mental health of Japanese employees.
著者
Shyam PINGLE
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.50, no.3, pp.167-171, 2012 (Released:2012-06-16)
参考文献数
9
被引用文献数
28 36

India, a growing economy and world’s largest democracy, has population exceeding 1.2 billion. Out of this huge number, 63.6% form working age group. More than 90% work in the informal economy, mainly agriculture and services. Less than 10% work in the organized sector; mainly industry, mining and some services. New service industries like Information Technology (IT), Business Process Outsourcing (BPO) are increasing rapidly; so is the proportion of females in the workforce. The occupational safety and health (OSH) scenario in India is complex. Unprecedented growth and progress go hand in hand with challenges such as huge workforce in unorganized sector, availability of cheap labor, meager public spending on health, inadequate implementation of existing legislation, lack of reliable OSH data, shortage of OSH professionals, multiplicity of statutory controls, apathy of stakeholders and infrastructure problems. The national policy on OSH at workplace, adopted by the government in 2009, is yet to be implemented. Some of the major occupational risks are accidents, pneumoconiosis, musculoskeletal injuries, chronic obstructive lung diseases; pesticide poisoning and noise induced hearing loss. The three most important OSH needs are: 1. legislation to extend OSH coverage to all sectors of working life including the unorganized sector; 2. spreading the awareness about OSH among stakeholders; 3. development of OSH infrastructure and OSH professionals. Other issues include integration of occupational health with primary health care.
著者
Massimo BATTAGLIA Marco FREY Emilio PASSETTI
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.52, no.4, pp.354-366, 2014 (Released:2014-09-11)
参考文献数
36
被引用文献数
22 28

Accidents at work are still a heavy burden in social and economic terms, and action to improve health and safety standards at work offers great potential gains not only to employers, but also to individuals and society as a whole. However, companies often are not interested to measure the costs of accidents even if cost information may facilitate preventive occupational health and safety management initiatives. The field study, carried out in a large Italian company, illustrates technical and organisational aspects associated with the implementation of an accident costs analysis tool. The results indicate that the implementation (and the use) of the tool requires a considerable commitment by the company, that accident costs analysis should serve to reinforce the importance of health and safety prevention and that the economic dimension of accidents is substantial. The study also suggests practical ways to facilitate the implementation and the moral acceptance of the accounting technology.
著者
Noriyuki NAKANISHI Toshio TAKATORIGE Kenji SUZUKI
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.43, no.2, pp.295-301, 2005 (Released:2006-03-17)
参考文献数
35
被引用文献数
66 68

To examine the association between cigarette smoking and the risk of the metabolic syndrome (MS), 3,649 Japanese male office workers aged 35-59 yr who did not have a history of cardiovascular disease were enrolled in this study. 2,994 men without the MS at entry were followed up over a 7-yr period. A modified National Cholesterol Education Program definition with body mass index instead of waist circumference was used for the MS. With adjustment for age, family history of diabetes, alcohol intake, and regular physical activity, the odds ratios of the MS were 1.0 (referent), 1.30 (95% confidence interval (CI), 1.00-1.68), 1.07 (95% CI, 0.82-1.39), 1.17 (95% CI, 0.88-1.56), and 1.66 (95% CI, 1.24-2.20) for never smokers, ex-smokers, and those who smoked 1-20 cigarettes/d, 21-30 cigarettes/d, and ≥31 cigarettes/d, respectively (P for trend for current smokers only =0.006). As for the risk of developing the MS, the respective multivariate-adjusted hazard ratios of developing the MS were 1.0 (referent), 1.43 (95% CI, 1.14-1.79), 1.14 (95% CI, 0.91-1.44), 1.45 (95% CI, 1.14-1.84), and 1.59 (95% CI, 1.24-2.05) (P for trend for current smokers only =0.001). Among men without the MS at entry, body weight gain over 7 yr, compared with never smokers, was significantly higher in smokers who quit smoking. It is important for the prevention of the MS not only to quit smoking but also to prevent weight gain after smoking cessation.
著者
Koji MORI Toru TAKEBAYASHI
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.40, no.2, pp.167-174, 2002 (Released:2007-03-29)
参考文献数
7
被引用文献数
11 14

An important challenge to occupational health services in Japan is the necessary shift from regulation-based occupational health program to health risk-based program. The Occupational Safety and Health Management System (OSHMS) is an effective tool for introducing risk-based activities. To date, the Five Management system has been used to manage occupational health activities. This classification, however, does not show the interactions among the listed activities. Nor is it clear how this system contributes to the PDCA (Plan/Do/Check/Act) cycle for continual improvement. The category in the Five Management system called “Roles of the Occupational Physician” covers most of the occupational health services required in Japan. The items listed in the Five Management system were compared to the guidelines of OSHMS from the International Labour Office and issues that should be solved for occupational health activities with OSHMS were clarified. Seven issues are discussed in this paper; (1) occupational safety and health policy and audit that can drive the PDCA cycle effectively, (2) reclassification of occupational health activities with several different objectives, (3) set up of targets, (4) risk assessment methods that can prioritize health risks compared to safety risks, (5) exposure assessment methods for risk assessment, (6) flexibility of laws and regulations, and (7) development of talented professionals for risk-based occupational health activities.
著者
Davood AFSHARI Seyed Mahmood LATIFI Samira KORD Maryam NOUROLLAHI-DARABAD
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.56, no.4, pp.327-335, 2018 (Released:2018-07-27)
参考文献数
38
被引用文献数
4 6

In 2011, load limits for manual lifting were adopted in Iran to protect workers from low back injury without prior testing of accuracy with Iranian workers. This investigation examined how accurate the adopted ACGIH TLVs at the allowable limits predict risk for LBP disorders for a group of Iranian workers using biomechanical criteria. Testing took place in the laboratory with participants completing a series of 2-handed lifting tasks as defined in the Iranian Guideline for Manual Lifting. To test accuracy, both compression and shear forces were estimated for fifteen male Iranian workers who completed 25 lift combinations that varied in height and reach with the maximal allowable load. The findings, when compared to a risk threshold of 3400 N compression and 700 N shear, showed above-threshold forces for compression and little-to-no safety margins with repetitive lifting for most lifts at torso height and below. Since Government, employers and workers use these guidelines to decide on work/workplace design; these guidelines require further review and revision based on the anthropometrics of Iranian people.
著者
Jun OJIMA
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.58, no.5, pp.479-486, 2020 (Released:2020-10-08)
参考文献数
1
被引用文献数
2 1

The Japanese Industrial Safety and Health Act was first enacted in 1972. The purpose of this Act is to secure the safety and health of workers in the workplace, as well as to facilitate the establishment of a comfortable work environment. To fulfill these purposes, the Industrial Safety and Health Act aims to clarify the responsibility system in the workplace and to promote proactive efforts by both employers and employees to maintain safety and health in the workplace. Specifically, it is expected that occupational accidents will be prevented by obligating employers to appoint safety and health personnel in accordance with the Act. In this paper, I introduce the features and key points of the Industrial Safety and Health Act, especially in relation to Chapter 3 (Articles 10–19), which provides for the organization of the safety and health management system. In addition, I describe recent amendments to the Act.
著者
Bruno LEMKE Tord KJELLSTROM
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.50, no.4, pp.267-278, 2012 (Released:2012-08-10)
参考文献数
46
被引用文献数
174 229

The WBGT heat stress index has been well tested under a variety of climatic conditions and quantitative links have been established between WBGT and the work-rest cycles needed to prevent heat stress effects at the workplace. While there are more specific methods based on individual physiological measurements to determine heat strain in an individual worker, the WBGT index is used in international and national standards to specify workplace heat stress risks. In order to assess time trends of occupational heat exposure at population level, weather station records or climate modelling are the most widely available data sources. The prescribed method to measure WBGT requires special equipment which is not used at weather stations. We compared published methods to calculate outdoor and indoor WBGT from standard climate data, such as air temperature, dew point temperature, wind speed and solar radiation. Specific criteria for recommending a method were developed and original measurements were used to evaluate the different methods. We recommend the method of Liljegren et al. (2008) for calculating outdoor WBGT and the method by Bernard et al. (1999) for indoor WBGT when estimating climate change impacts on occupational heat stress at a population level.
著者
Jun OJIMA
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.49, no.3, pp.393-395, 2011 (Released:2011-06-14)
参考文献数
10
被引用文献数
5 7

Charcoal, often used as cooking fuel at some restaurants, generates a significant amount of carbon monoxide (CO) during its combustion. Every year in Japan, a number of cooks and waiters/waitresses are poisoned by CO emanating from burning charcoal. Although certain ventilation is necessary to prevent the accumulation of CO, it is difficult to estimate the proper ventilation requirement for CO because the generation rate of CO from burning charcoal has not been established. In this study, several charcoals were evaluated in terms of CO generation rate. Sample charcoals were burned in a cooking stove to generate exhaust gas. For each sample, four independent variables — the mass of the sample, the flow rate of the exhaust gas, CO concentration in the exhaust gas and the combustion time of the sample — were measured, and the CO generation rate was calculated. The generation rate of CO from the charcoal was shown to be 137-185 ml/min/kW. Theoretical ventilation requirements for charcoals to prevent CO poisoning are estimated to be 41.2-55.6 m3/h/kW.
著者
Yusaku MORITA Koji KANDABASHI Shigeyuki KAJIKI Hiroyuki SAITO Go MUTO Takahiro TABUCHI
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.60, no.4, pp.360-370, 2022-05-11 (Released:2022-08-01)
被引用文献数
2

This study evaluated the relationship between occupational injury risk and gig work, which included the exchange of labor for money between individuals or companies via digital platforms. As Japan has experienced a severe economic decline during the coronavirus disease 2019 (COVID-19) pandemic, an increasing number of individuals have engaged in gig work. While few studies have evaluated occupational risks in gig work, several traffic accidents associated with food delivery gig work have been reported in the mass media. In this study, 18,317 individuals completed an internet survey that collected information pertaining to their involvement in gig work and experience of related occupational injuries; data regarding several confounding factors were also recorded. Multiple logistic regression analysis showed that workers involved in gig work had a greater risk of any minor occupational injuries (odds ratio, 3.68; 95% confidence interval, 3.02–4.49) and activity-limiting injuries (odds ratio, 9.11; 95% confidence interval, 7.03–11.8) than those not involved in gig work, after adjusting for age, sex, household income, lifestyle factors, and work-related factors. The results of this study indicate that gig workers are exposed to greater occupational hazards during the COVID-19 pandemic. Additional studies are warranted to clarify the causal mechanism for this relationship.
著者
Christopher B. JONES Jillian DORRIAN Shanthakumar M.W. RAJARATNAM
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.43, no.1, pp.63-70, 2005 (Released:2006-03-17)
参考文献数
44
被引用文献数
14 31

Fatigue is an increasingly recognised risk factor for transportation accidents. In light of this, there is the question of whether driving whilst fatigued should be a criminal offence. This paper discusses the current legal position, including the problems of voluntary conduct and self awareness. Three models for reform are proposed. The manner in which scientific research can inform legal consideration and future directions for research are discussed.
著者
Naoki SHIOTA Tomohiro ISHIMARU Makoto OKAWARA Yoshihisa FUJINO Takahiro TABUCHI
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.60, no.3, pp.216-223, 2021-10-15 (Released:2022-06-01)
被引用文献数
4

This study aimed to evaluate the association between work-related changes caused by COVID-19 and psychological distress among Japanese workers. The cross-sectional study was conducted from August 25 to September 30, 2020. The participants were 15,454 employees who were registered as panelists with an online survey company. The Kessler psychological distress scale with a 13-point cutoff was used to measure psychological distress. Multiple logistic regression was performed. Of the respondents, 8.9% were evaluated as having severe psychological distress. Among five examined work-related changes, being laid off and changing jobs (adjusted odds ratio [aOR] = 5.43; 95% confidence interval [CI]: 4.18–7.05), experiencing temporary workplace closure (aOR = 1.94; 95% CI: 1.67–2.25), being forced to visit the workplace for paperwork (aOR = 1.84; 95% CI: 1.58–2.15), and starting telework from home (aOR = 1.18; 95% CI: 1.01–1.37) were associated with increased psychological distress; no significant association was found for participation in work-related online meetings. The impact on psychological distress was greater among men, especially for being laid off and changing jobs because of COVID-19. It is important to assess and reduce negative mental health effects among workers experiencing work-related changes caused by the COVID-19 pandemic, taking gender differences into account.
著者
Giovanna CASTELLINI Dario CONSONNI Giovanni COSTA
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
pp.2021-0283, (Released:2022-03-15)
被引用文献数
1

Interpersonal conflicts at workplace are increasing in relation to high competitiveness and pressures at work, mainly connected with labor market globalization. Their manifestation is multifaceted in relation to different working conditions and they not only hinder health, performance, and job satisfaction, but can also harm people's rights and dignity. The study analyses issues related to work conflicts and adverse health consequences in 1,493 workers who approached a hospital service for work-related stress and harassment over a 3-year period. The subjects were examined according to a broad protocol covering working conditions, sources of conflict and negative actions suffered, and resulting impact on health status. Many critical conditions were reported in all occupational sectors with some differentiation in relation to gender (women more at risk) and employment status. Higher qualified levels were more exposed to experiencing severe personal adversities aimed at their progressive expulsion or resignation, with consequent higher risk of chronic adjustment disorders, while lower levels reported more stressful conditions in terms of interpersonal disputes and greater interference in the home-work interface. The study can provide useful indications for a better understanding of workplace conflicts in order to set up the most appropriate actions to manage and prevent them.
著者
Toshiki FUKUZAKI Noboru IWATA
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.60, no.2, pp.154-163, 2021-10-15 (Released:2022-04-01)
被引用文献数
7

The purposes of this meta-analysis were (1) to examine the associations between work engagement (WE) and the personality dimensions of five-factor model and (2) to determine how much variance in WE is explained by these five factors. We performed a database search for studies related to personality traits and WE, and 36 papers that reported correlation coefficients were selected for the meta-analysis. After correcting for publication bias using the trim-and-fill method, conscientiousness had the strongest association with WE (ρ=0.41), followed by extraversion and openness to experience (0.38), neuroticism (−0.36), and agreeableness (0.27). Moreover, 30% of the WE variance could be explained by the five-factor model (R2=0.33, 95%CI=0.26–0.49) according to a path analysis using the weighted average correlation for unreliability. This proportion was higher than that from a previous meta-analysis of job satisfaction and job performance and was lower than that of personality and WE. Thus, to enhance WE, it is necessary to evaluate both the personality and the psychosocial work environment in detail.
著者
Puriene Alina Aleksejuniene Jolanta Petrauskiene Jadvyga BALCIUNIENE Irena JANULYTE Vilija
出版者
独立行政法人 労働者健康安全機構 労働安全衛生総合研究所
雑誌
Industrial health (ISSN:00198366)
巻号頁・発行日
vol.46, no.4, pp.369-374, 2008
被引用文献数
51

This article describes the second phase of a large study of Lithuanian dentists' health, and focuses on self-reported physical health complaints, general health state and associations between the two. In 2006, a postal questionnaire survey of all (N=2,449) licensed dentists registered with the Lithuanian Dental Association was conducted, obtaining a response rate of 68.2%. Fatigue (94.7%) and back pain (91.0%) were the most prevalent physical complaints reported, and they were also the most likely to become chronic among all physical disorders. Hypertension, joint diseases and allergy were the most prevalent diagnosed and treated diseases during the previous 12 months. Only half of the surveyed Lithuanian dentists (50.4%) rated their health as satisfactory. Logistic regression revealed that fatigue (Odds Ratio: 0.52; 95%CI: 0.29-0.94), headache (OR: 0.62; 95%CI: 0.42-0.90), hand problems (OR: 0.62; 95%CI: 0.44-0.87), chest pain (OR: 0.51; 95%CI: 0.40-0.64) and musculoskeletal complaints (OR: 0.41; 95%CI: 0.28-0.60) had a significant negative impact on dentists' self-reported general health. Overall, this study suggests that Lithuanian dentists do experience a certain amount of occupationally-related health problems. It is therefore important to increase health knowledge on occupational hazards and also to emphasize the importance of early diagnosis and treatment for these disorders in Lithuania, as elsewhere.<br>
著者
Sang-il LEE Takeshi NISHI Masaya TAKAHASHI Shigekazu HIGUCHI
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.59, no.6, pp.393-402, 2021-09-27 (Released:2021-11-29)
被引用文献数
2

A nighttime nap is expected to mitigate melatonin suppression during night work by blocking light input to the retina, but it is unclear. In the present study, we investigated the effects of a nap break on melatonin level, subjective sleepiness, and vigilance performance during simulated night work. Eleven healthy young males (mean ± SD age: 22.2 ± 4.1 years) participated in counterbalanced crossover design experiments with two conditions (nap vs. no nap). The subjects performed 12-hour simulated night work from 21:00 to 09:00 h (illuminance: ~500 lx). Subjects with a nap condition took a nap for 2 hours in a dark room from 03:00, while subjects with a no nap condition continued the simulated night work. The results showed that immediately after the 2-h nap break, the melatonin level at 05:00 h temporarily recovered from light-induced melatonin suppression during the simulated night work but significantly suppressed again at 07:00 and 09:00 h. Subjective alertness and vigilance performance were impaired immediately after the nap break but subsequently enhanced. The results suggest that a single nap break for 2 hours could be a strategy to enhance alertness during the last part of night shift but inadequate for mitigating melatonin suppression.
著者
Antonio VALENTI Grazia FORTUNA Caterina BARILLARI Erika CANNONE Valeria BOCCUNI Sergio IAVICOLI
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
vol.59, no.5, pp.334-339, 2021-08-18 (Released:2021-10-05)
被引用文献数
16

The global spread of COVID-19 pandemic forced the scientific community to identify new ways of exchanging and transferring the scientific knowledge, also considering that the measures taken to combat the pandemic, such as travel restrictions, closed borders and gathering bans, led to cancellations of many conferences, meetings and workshops. The enhancement of the existing digital platforms and the development of new systems to share scientific knowledge has allowed the scientific community to “meet” again in new virtual environments (e.g., Zoom, Cisco WebEx, Live Stream, Demio, GoToWebinar Seminar, Google Hangouts, Skype, Microsoft Teams, etc.), providing an unprecedented opportunity to reform methods of organizing academic conferences in all disciplines.Starting from the review of the existing literature, this study aimed at investigating the impact of the spreading of virtual conferences on the field of research. The SWOT analysis was used to identify strengths and weaknesses of the scientific conferences organized in the new format, as well as opportunities and threats created by the socio-economic and political context in the era of the COVID-19 pandemic.
著者
Sang-il LEE Takeshi NISHI Masaya TAKAHASHI Shigekazu HIGUCHI
出版者
National Institute of Occupational Safety and Health
雑誌
Industrial Health (ISSN:00198366)
巻号頁・発行日
pp.2020-0245, (Released:2021-09-28)
被引用文献数
2

A nighttime nap is expected to mitigate melatonin suppression during night work by blocking light input to the retina, but it is unclear. In the present study, we investigated the effects of a nap break on melatonin level, subjective sleepiness, and vigilance performance during simulated night work. Eleven healthy young males (mean ± SD age: 22.2 ± 4.1 years) participated in counterbalanced crossover design experiments with two conditions (nap vs. no nap). The subjects performed 12-hour simulated night work from 21:00 to 9:00 h (illuminance: ~500 lx). Subjects with a nap condition took a nap for 2 hours in a dark room from 3:00, while subjects with a no nap condition continued the simulated night work. The results showed that immediately after the 2-h nap break, the melatonin level at 5:00 h temporarily recovered from light-induced melatonin suppression during the simulated night work but significantly suppressed again at 7:00 and 9:00 h. Subjective alertness and vigilance performance were impaired immediately after the nap break but subsequently enhanced. The results suggest that a single nap break for 2 hours could be a strategy to enhance alertness during the last part of night shift but inadequate for mitigating melatonin suppression.