Sleep and wakefulness are physiological processes in our lives that are regulated by circadian rhythms. The level of melatonin, the "sleep hormone", increases with the onset of darkness, and its production slows down in the morning. Exposure to artificial light at night disrupts our circadian rhythm and the processes it controls. Shift work is when an individual works from 9 am to 5 pm. But the night shift refers to the time when a group of workers who work at night in factories and enterprises work in the evening or at night, especially from 4 p.m. to 8 a.m. according to a regular schedule. One in five people in industrialized countries work night shifts, and studies in America and Europe show that between 15 and 30% of adult workers have some form of shift work. Between 10% and 30% of shift workers meet the diagnosis of shift work disorder (SWD). 5-10% of shift workers experience severe shift insomnia and sleepiness. At least ¾ of shift workers suffer from insomnia. Excessive sleepiness usually occurs during shifts (mainly at night) and is associated with impaired cognitive ability due to the need for sleep and reduced alertness, and decreased alertness reduces performance. Job performance is influenced by many workplace environmental factors, including workload, coworker relationships, stress levels, and extended hours. A nurse specialist provides nursing care by monitoring and evaluating 24 hours a day, and by working night shifts, the circadian system of sleep is disturbed, causing sleep problems and insomnia. When examining how night shift work affects nurses' ability to concentrate, the decline in concentration (33.3%) was twice as high as that of day shift nurses (16.7%). found that shift nurses who worked the night shift had higher rates of insomnia and chronic fatigue compared to nurses who stopped working the night shift. Lack of sleep manifests as a decline in cognitive functions such as attention, decision making, and reaction time. These cognitive and functional declines can negatively affect quality of life and lead to impaired job performance. An Australian study by Winwood et al found that fatigue associated with night shifts increases the risk of human error and injury, and negatively affects the quality of patient care. Lack of sleep significantly affects nurses' alertness, concentration, and job performance. This review article discusses the relation between shift work-related sleep and job performance based on international research findings.

Introduction: 5-10% of shift workers experience severe shift insomnia and sleepiness. A nurse specialist stays by the client's side 24 hours a day, assesses and monitors their physical condition, and provides nursing care. In a comparative study on the work activity among shift nurses, night shift nurses were less active (40%) and more fatigued (53.3%) than day shift nurses.
An aspects of chronotype and sleep quality in shift nurses does not established in Mongolia and the data is very rare, and we aimed to conduct this study. Goal: To study shift schedule, sleep quality and individual chronotype of shift nurses. Materials and Methods: This study is a cross-sectional study. The survey was completed between July 1, 2023 and December 31, 2023, and included a total of 117 nurses who met the inclusion and exclusion criteria of the BZDGH, SKDGH, and KUDGH research. In collecting research data, the questionnaires "Insomnia Severity Index", which is a commonly used international standard questionnaire for assessing insomnia, The Munich Chrono Type Questionnaire for assessing individual chronotype, and "Karolinska Sleepiness Scale" were used. The ethical approval: The ethical approval for the study was obtained by a decision of the Ach Medical University-Ethical Committee on Research on June 30, 2023 (2023/02/05). Statistical analysis : Results were calculated using SPSS - 21.0 v program by a descriptive statistic, and the Pearson correlation analysis. Results : The average score of the Insomnia Severity Index (ISI) was 12.60±6.38, which is the sub threshold for clinical insomnia. But the average Karolinska Sleepiness Scale (KSS) score for sleepiness is 4.41±2.50, or moderate alertness during the shift. Workday sleep-wake pattern and non-workday sleep-wake pattern are correlated (r=0.44, p=0.001). Also, individual chronotype is correlated with chronotype of non-working days (r=0.23, p=0.02). Conclusions Nurses' sleep quality levels were pre-clinical insomnia and moderate alertness during shifts for sleepiness. Working and non-working day sleep-wake patterns are different, chronotype is medium early type. The sleep-wake pattern of weekdays and the sleep-wake pattern of non-workdays are related to each other. The chronotype of the individual is related to the chronotype of non-working days.