Shift and night work

What are shift work and night work?

Sectors such as healthcare, continuous process manufacturing, transportation, security, hospitality, and emergency services need to cover operations beyond the daytime hours. Shift work (rotating, fixed, morning, afternoon, and night shifts, in cycles of varying duration) and night work are the organizational solution, but they come at a cost to people’s health and lives: the human body is programmed for daytime activity and nighttime rest, and working against this rhythm can disrupt sleep and contribute to fatigue, errors and work-life difficulties; research also describes associations with digestive, cardiovascular and mental-health problems. The Epworth Sleepiness Scale can be used to screen for daytime sleepiness in health surveillance , but it does not, on its own, determine fitness for the job.

The Workers’ Statute establishes basic rules: the working day of night workers cannot exceed an average of eight hours per day over a reference period of fifteen days; these workers cannot work overtime; night work has specific remuneration unless it is compensated with rest periods or the salary has been established taking into account its nighttime nature; in companies with production processes continuing throughout the twenty-four hours, no worker should remain on the night shift for more than two consecutive weeks unless voluntarily assigned; and night workers must enjoy a level of safety and health protection adapted to the nature of their work, with free health assessments before assignment to night work and at regular intervals.

From a preventative standpoint, shift work and night work are psychosocial and organizational risk factors that must be assessed (Law 31/1995, Articles 4.7 and 16) and managed using ergonomic and chronobiological criteria, such as those described in INSST Technical Note 455. Directive 2003/88/EC on the organization of working time constitutes the European framework.

Effects on health and safety

• Circadian rhythm disruption. Mismatch between the biological clock and work schedule, with shorter and poorer quality daytime sleep, nighttime sleepiness, and accumulated fatigue.
• Physical health. Digestive disorders due to irregular meal times, increased cardiovascular and metabolic risk, and association with certain long-term health problems.
• Mental and social health. Irritability, anxiety, work-life balance difficulties, social isolation, and family conflicts.
• Safety. Reduced performance and attention during off-peak hours (early morning), with an increase in errors and accidents, including traffic accidents at the end of the night shift.
• Vulnerable groups. Particular sensitivity is assessed against personal characteristics and job risks. Age alone does not establish an exemption; adaptations and maternity or breastfeeding protection follow the assessment and applicable law.

Preventive organization criteria

• Rotation design. Short forward rotation (morning, afternoon, night) is a preventive option to assess with workers and against job demands; it is not a universal solution. Limiting consecutive nights and ensuring recovery requires a context-specific schedule that respects statutory minima.
• Schedules. Avoid very early starts to the morning shift, maintain regular and predictable schedules, and allow some participation in the selection.
• Breaks and rest periods. Sufficient breaks for meals at reasonable times, the possibility of resting at night when the activity allows, and grouped days off.
• Workload. Reduce the most demanding or risky tasks during off-peak hours and adjust night shifts.
• Environment. Adequate lighting at night, temperature and food services available.
• Health monitoring and training. Specific check-ups, information on sleep hygiene, nutrition and driving after the shift, and attention to signs of intolerance.

Organizational application: how to manage shifts and night work

1. Include shift and night work in the assessment of psychosocial and organizational risks, with data on absenteeism, accidents by time slot and staff perception.
2. Design the shift system by assessing rotation options, consecutive nights and available recovery, consulting representatives and checking the results.
3. Adjust the workload and critical tasks on the night shift and ensure adequate staffing and supervision.
4. Apply the limits of the Workers’ Statute: night shift, overtime, maximum stay and compensation.
5. Organize specific health monitoring before and periodically after assignment, and manage adaptations for people with intolerances, older age, pregnancy or breastfeeding.
6. Training in sleep hygiene, nutrition, driving after shift work, and fatigue detection.
7. Measure and review: indicators of accidents and incidents per shift, absenteeism, turnover and satisfaction with the system.

Preventive management software allows you to link shifts with accident rates and absenteeism, plan specific health monitoring, and record adaptations and consultations with representatives.

Limits and common mistakes

1. Designing shifts based solely on production criteria, without considering physiological tolerance or consulting the staff.
2. Exceeding the maximum night shift or assigning overtime to night workers.
3. Maintaining a rotation system without checking its effects on recovery and workers’ needs.
4. Not offering prior and periodic health assessments or managing detected intolerances.
5. Concentrating critical or maintenance tasks in the early morning without reinforcement or supervision.
6. Forget the risks of driving home after the night shift.

Exceptions must meet the applicable legal conditions, including Articles 32 and 33 of Royal Decree 1561/1995. A collective agreement does not freely override working-time and rest limits; this article is informational.

Regulatory framework in Spain

• Royal Legislative Decree 2/2015, Workers’ Statute, Article 36. Night work, shift work and work rhythm: definitions, limits and health protection.
• Law 31/1995, articles 4.7, 15, 16, 22, 25 and 26. Working conditions, adaptation of work to the person, evaluation, health surveillance and protected groups.
• NTP 455 of the INSST . Shift and night work: organizational aspects.
• Directive 2003/88/EC of the European Parliament and of the Council of 4 November 2003. Organization of working time: night work, shift work and work pace.

ILO Convention 171 on night work establishes measures for the protection of health and maternity. In Colombia, the Substantive Labor Code regulates night shift differentials, and the Occupational Health and Safety Management System (SG-SST) requires the evaluation of risks arising from the organization of working time.

Recovery, circadian rhythms and mental health

Assessment should reconstruct the hours actually worked: nights, extensions, unexpected changes, breaks between shifts, travel and opportunities for recovery. Two schedules with identical monthly hours may create different demands. Accumulated fatigue may present as reduced attention, irritability or errors, but these signs do not independently identify a mental disorder or establish its occupational origin. Organisational data should be considered alongside workers’ experience and clinical assessment where appropriate.

Chronoprevention can describe incorporating biological rhythms into work design; it is not a diagnostic method or a standardised legal scale. Before changing a rotation, define the problem, alternatives, necessary staffing and how results will be assessed. Comparing incidents per hours worked, urgent schedule changes and real opportunities for rest is more informative than attributing every difference to night work. Breaks or training do not compensate for insufficient staffing or remove the obligation to respect working-time and rest requirements.

Age, working history and urban maintenance at night

Chronological age does not independently determine capacity for night work. Individual tolerance, accumulated exposure, task demands and preventive conclusions from occupational health surveillance matter. Where a problem arises, review the job and compatible alternatives; do not automatically exclude everyone in an age band or require disclosure of diagnoses to a manager. In Spain, the employer receives the necessary conclusions about fitness and measures within the confidentiality limits of Article 22 of the Occupational Risk Prevention Act.

Urban maintenance at night combines scheduling, traffic, visibility, noise, physical tasks and changing locations. A proposed arrangement should cover handovers, communication, incident response and a safe way to finish work if sleepiness appears. Rescheduling an intervention or increasing staffing may be necessary depending on assessment. Experience does not eliminate fatigue, and assigning supposedly light tasks alone does not demonstrate that exposure is controlled.

Digital work at night and protected rest

Digital continuity can extend a working day after someone has left the site. Distinguish a planned night shift, a regulated on-call arrangement and messages intruding on rest. Spain’s disconnection policy under Article 88 of Organic Law 3/2018 includes management positions and is prepared after hearing workers’ representatives. A scheduling application should show assignments and provide a defined route for communicating changes, without requiring constant monitoring of a phone.

Prevention can include handovers within organised working time, channels for actual incidents, absence cover and scheduled delivery of non-urgent communications. Screen light and cognitive stimulation are part of the context of sleep; they should not be used to blame individuals who receive instructions outside working hours. Persistent sleep difficulties require professional assessment and review of work, rather than an automatic productivity score.

What the evidence on oxidative stress can establish

IARC Monograph 124 examines biological mechanisms associated with night work, including oxidative stress. Mechanistic research does not amount to a validated individual test that establishes how much harm a particular schedule has caused. A diagnosis, fitness decision or need for supplements should not be inferred from an isolated biomarker. IARC classification identifies a carcinogenic hazard; it does not calculate individual risk or establish that everyone exposed will develop cancer.

In practice, organisations need to reduce avoidable exposures, respect rest periods, provide relevant occupational health surveillance and review conditions that impede sleep and recovery. Monitoring symptoms and events must protect confidentiality. An improvement reported in a questionnaire does not replace checking actual changes in working hours, workload, staffing and recovery.