Working overnight or putting in excessively long hours may take a toll on workers’ health, with research linking these work patterns to higher risks of cardiovascular disease, diabetes, sleep problems and workplace accidents.
For many workers, night shifts are unavoidable. Security personnel, healthcare workers, drivers and employees in other 24-hour services often work while most people are asleep.
However, repeatedly staying awake at night can disrupt the body’s natural sleep-wake cycle, while long working hours can leave workers with insufficient time to recover.
Long working hours linked to hundreds of thousands of deaths
The World Health Organization (WHO) and International Labour Organization (ILO) estimated that exposure to working 55 hours or more per week was associated with 745,000 deaths from stroke and ischemic heart disease globally in 2016.
Compared with people working 35 to 40 hours a week, those working at least 55 hours had an estimated 17% higher risk of ischemic heart disease and a 35% higher risk of stroke.
The WHO and ILO estimates also show that deaths associated with long working hours have increased over time, highlighting the health burden associated with excessive work schedules.
Night shifts disrupt the body clock
The human body follows a roughly 24-hour biological cycle known as the circadian rhythm, which helps regulate sleep, wakefulness and other bodily functions.
Night workers are required to remain alert during a period when the body is naturally prepared for sleep. Regular disruption of this cycle can make it harder to obtain sufficient, restorative sleep.
Sleeping during the day can also be challenging because of daylight, noise and other environmental disruptions, particularly for workers who have spent the night on duty.
Cancer risk also under investigation
Night shift work has also been identified as a potential cancer hazard.
The International Agency for Research on Cancer (IARC), the cancer research agency of WHO, classified night shift work as “probably carcinogenic to humans” (Group 2A). The classification was based on limited evidence in humans and stronger evidence from experimental studies.
IARC identified evidence concerning breast, prostate, colon and rectal cancers, but the classification does not mean that every person who works at night will develop cancer.
Fatigue can increase accident risks
The effects of night work and long hours can also appear in the short term.
Fatigue and inadequate sleep can reduce alertness, concentration and reaction time, increasing the likelihood of mistakes and accidents, particularly in jobs that require workers to remain highly attentive.
Drivers, healthcare workers, security personnel and people operating machinery may face particular challenges when required to work through the night or for extended periods.
Night work combined with long hours can also contribute to stress and make it harder for workers to maintain a healthy balance between work and recovery.
More work does not always mean better health
For workers who depend on overtime or night shifts to increase their income, reducing working hours may not always be an easy choice.
However, evidence on long working hours and night shifts highlights the importance of adequate rest and reasonable work schedules.
The research does not mean that every person who works at night will develop a serious illness. Rather, it shows that repeated exposure to night work and excessively long hours can increase health and safety risks, making adequate rest and recovery an important part of protecting workers’ wellbeing.
