How does night shift work affect the body clock, sleep and workplace safety? Read the research findings and practical shift measures employers can put in place.
It is four in the morning. The factory lights are on and the machines are running, but the body of the operator at the head of the line has been telling them for hours that it should be asleep. Their eyes grow heavy, their reactions slow down, and they read the same line twice. This tiredness is not down to laziness or a lack of motivation; it is a natural consequence of human biology. Night shift work is indispensable for factories with continuous production, hospitals, logistics centres and security services, yet it conflicts directly with the human sleep-wake cycle. In this article I look at how working at night affects the body clock, sleep, mental health and workplace safety, and at what employers, HR managers and occupational health and safety (OHS) specialists can do to reduce these risks.
What Are the Body Clock and the Sleep-Wake Cycle?
The human body runs on an internal clock of roughly 24 hours. Besides sleep and wakefulness, this clock regulates body temperature, hormone release, digestion and alertness. Its strongest regulator is light: daylight tells the body to "stay awake", while darkness starts the preparation for sleep.
As a natural result of this system, attention and alertness fluctuate over the course of the day. After midnight, and especially in the early hours before dawn, alertness naturally falls to its lowest level. A milder dip also occurs in the afternoon. A person working at night has to carry out the tasks that demand the most attention at precisely the hours when the body is at its sleepiest.
Sleeping during the day is not the same as sleeping at night. Daylight, heat, traffic and household noise all interrupt sleep. Because the body is programmed to be awake during daytime hours, sleep can be both shorter and shallower. As a result, a significant proportion of night workers build up a chronic sleep debt. Returning to a daytime routine on days off, so as to take part in family and social life, also means the internal clock is constantly being shifted back and forth, which is similar to the exhaustion felt by a traveller who crosses time zones frequently. This is why the effect of night work is not confined to the hours of the night itself; it spreads across the whole week.
How Does Night Shift Work Affect Sleep and Health?
Sleep debt and chronic fatigue
Sleeping a few hours too little every day adds up over weeks. A person may come to accept this as "normal" over time, but attention, memory, decision-making and reaction time continue to suffer from the accumulated deficit. In the OSH Pulse 2022 survey carried out in Europe, general fatigue came first among the health problems caused or made worse by work, at 37% (EU-OSHA, 2022). For advice on individual sleep problems, you can read the article on how to overcome insomnia.
Mood and emotional regulation
Insufficient and irregular sleep can go hand in hand with irritability, impatience, anxiety and a low mood. A sleep-deprived mind reacts more strongly to negative events and finds it harder to cope with stress. This spills over into relationships at work and into family life. According to Gallup's 2026 report, 66% of employees in Turkey say they experienced stress during a large part of the previous day (Gallup, 2026; 2025 data); for employees whose sleep pattern is disrupted, carrying this burden is harder still.
Physical health
Irregular meal times, night-time snacking, inactivity, digestive complaints and increased caffeine consumption are common among night workers. In its 2019 evaluation, the International Agency for Research on Cancer (IARC) classified night shift work as "probably carcinogenic to humans" (Group 2A); this covers factory workers too. However, IARC also states clearly that the evidence in humans is limited (IARC, 2020). This information matters not to cause alarm, but as a reminder that night work needs to be taken seriously and managed well from a health point of view.
Social and family life
A person who works at night lives on a different clock from the rest of society. Time spent with family, social events and friendships can shrink over time. I discuss this dimension in detail in the article on family life for shift workers.
The tiredness of someone who works at night is not a problem of willpower but a biological fact; a good shift pattern does not ignore this fact, it takes it into account.
Night Shift Work and Workplace Safety
Alertness that drops in the early morning hours is a direct risk factor for workplace safety. According to Folkard and Tucker's 2003 review, productivity and safety can deteriorate during the night; safety worsens over consecutive nights, with longer working hours, and as the time between breaks lengthens. According to figures reported with reference to this review:
- In an 8-hour shift system, the risk of an accident or injury is about 18% higher on the afternoon shift than on the morning shift, and about 30% higher on night work.
- Compared with the first night, the risk rises by about 6% on the second night, 17% on the third night and 36% on the fourth night.
- By the 12th hour of a shift, the risk is more than double the average of the first 8 hours (Folkard and Tucker, 2003).
These findings show that what matters in night work is not only "how many people" work at night, but also "how many nights in a row" and "for how many hours". In other words, when the same number of night shifts is planned in different ways, very different levels of risk can emerge; in this respect, the shift schedule is a safety tool.
In 2025, Turkey recorded 766,039 workplace accidents and 1,931 deaths resulting from them; around 41% of the accidents occurred in the manufacturing sector (SGK, 2025). In Çorum, 3,821 workplace accidents and 12 deaths were recorded in the same year (SGK, 2025). Although these data contain no official breakdown of how many of these accidents happened at night, the role of fatigue in accidents has been shown consistently by international research. I discuss the wider safety dimension of shift patterns in detail in the article on shift work, fatigue and workplace safety.
Signs of Struggling on the Night Shift
The signs that someone working at night is struggling often appear gradually and may be dismissed, even by the person themselves, as "ordinary tiredness". Some signs that shift supervisors and OHS specialists can watch for are:
- Noticeably more errors, forgetfulness or slowing down in the last hours of the shift.
- Involuntary dozing during breaks or short pauses, with "eyelids dropping".
- Irritability, frequent arguments with teammates, impatience.
- Increased consumption of caffeine, energy drinks or cigarettes.
- Frequent headaches, stomach and digestive complaints, changes in appetite.
- Failing to recover even on days off, a constant feeling of exhaustion.
- A rise in absenteeism and sick leave, and more requests to swap shifts.
Suppose someone working as a forklift operator in a warehouse and distribution centre has been working four nights in a row for months. Because they have young children at home during the day, they can sleep no more than four or five hours. In recent weeks they have brushed against the racking lightly twice and once turned into the wrong aisle, but they have told no one, because they are afraid of appearing "careless". Although this picture looks like an individual attention problem, it is in fact a risk sign that has to be addressed by looking at the shift pattern, home sleeping conditions and the culture of reporting together.
Legal and Standards Framework
Article 4 of Occupational Health and Safety Law No. 6331 places an obligation on the employer to ensure the work-related health and safety of employees, and requires that an employee's fitness for the job in terms of health and safety be taken into account when assigning duties. Article 5 of the Law provides for a prevention policy that covers the effects of factors related to work organisation and working conditions. Article 10 requires that risk assessments take into account the situation of young, older and disabled workers, pregnant or breastfeeding workers, and women workers, while Article 15 requires health surveillance to be provided according to the risks employees are exposed to.
Article 8 of the Occupational Health and Safety Risk Assessment Regulation provides for the identification of sources of psychosocial hazards. In the 2024 Psychosocial Factors Information Guide of the Ministry of Labour and Social Security, "work schedules" appear as a separate psychosocial hazard category (ÇSGB, 2024). For specific legal provisions and time limits on night work, it is advisable to obtain up-to-date information from your employment law adviser.
What Can Employers and OHS Specialists Do?
- Limit the number of consecutive nights. Given that risk rises with consecutive nights, plan shorter runs rather than long night series. Leave enough recovery time after a run of nights.
- Consider the direction and speed of shift rotation. Rotating shifts forward, in the order morning, evening, night, generally makes it easier for the body to adapt. Review the rotation pattern together with the workplace physician and the OHS specialist.
- Keep shift length under control. In night work, avoid long shifts and overtime added to the end of a shift as far as possible. If a long shift is unavoidable, move the riskiest tasks to the first hours.
- Plan and protect breaks. Regular short breaks at night help refresh attention. Make sure breaks are actually taken, not just recorded on paper. A short walk, fresh air or a well-lit rest area can help restore attention in the early morning hours.
- Know the riskiest hours. In the early morning hours, reduce risky tasks that demand high attention and are carried out by one person; where possible, apply working in pairs, additional checks or task rotation.
- Improve the working environment. Provide adequate and suitable lighting in areas worked at night, a comfortable rest area, and the option of a hot, nourishing meal.
- Provide safe transport. A tired employee driving home in their own vehicle after a night shift increases the risk of a traffic accident. Plan the shuttle service with this risk in mind.
- Use health surveillance effectively. Together with the workplace physician, regularly assess sleep problems, fatigue, digestive complaints and mood changes among night workers. Discuss alternative arrangements for employees who clearly struggle to adapt to night work.
- Provide sleep and fatigue training. Give employees practical information on protecting daytime sleep, setting up the sleep environment, and the timing of caffeine and meals. If possible, run these sessions in a way that includes their families too.
- Make it safe to report fatigue. An employee being able to say "I'm very tired today, it would be risky for me to do this job" without being penalised is part of a strong safety culture.
How to Get Started in Your Organisation
- Needs analysis: Examine accident and near-miss records by time of day, shift type and number of consecutive nights. In an anonymous survey of night workers, ask about sleep duration and quality, fatigue, mood, family life and health complaints. Review the current shift schedule in terms of the number of consecutive nights, shift length and rest intervals.
- Programme: Based on the findings, prepare a plan consisting of improvements to the shift pattern, fatigue awareness training for shift supervisors, sleep health information for employees and their families, and individual psychological support where needed. Cognitive behavioural approaches can be helpful for sleep problems; whether medication is needed can only be decided by a physician.
- Measurement: After six months, compare night-time accident and near-miss indicators, absenteeism and staff turnover with the previous period, and repeat the survey.
You can find out how this process can be planned with the support of a psychologist on the corporate services page.
Frequently Asked Questions
Do people get used to working nights over time?
Partly. Some people adapt to night work more easily than others. However, because of the influence of daylight and social life, the body continues to tend towards being awake during the day; returning to a daytime routine on days off in particular makes full adaptation difficult. For this reason, rather than assuming people will "get used to it", it is safer to build a shift pattern that reduces the risks.
Is fixed night work or rotating shifts better?
There is no single right answer; it depends on the needs of the workplace and the situation of the employees. What matters is that the number of consecutive nights is kept reasonable, that enough rest time is left between shifts, and that the pattern is known in advance. The decision should be made together with the workplace physician and the OHS specialist.
How can someone who works at night improve their daytime sleep?
Keeping the bedroom as dark, cool and quiet as possible, avoiding bright light on the way home, not having caffeine in the last hours of the shift and not eating a heavy meal before sleep can all help. If sleep problems continue for a long time, support from a specialist is needed. The effect of the measures taken is greater when the family also knows about these sleep hours and helps to protect them.
Are there employees who are not suited to night work?
Certain health conditions, special circumstances such as pregnancy and breastfeeding, or marked sleep problems can make night work riskier. This assessment must be made by the workplace physician, within the framework of the legislation and according to the person's situation.
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Eda Erkan Alapala
Klinik Psikolog. İstanbul Kent Üniversitesi Klinik Psikoloji Tezli Yüksek Lisans mezunu; bilişsel davranışçı terapi, çocuk merkezli oyun terapisi ve çocuk-ergen psikoterapisi alanlarında eğitimlerini tamamlamıştır.
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