Night Work: Effects on Health and Prevention of Atypical Schedules

Night work disrupts the circadian rhythm and impacts health: sleep disorders, fatigue, cardiovascular risks. This article presents the effects, obligations, and preventive measures.

Night work disrupts the circadian rhythm and impacts health: sleep disorders, chronic fatigue, cardiovascular and metabolic risks. According to the International Agency for Research on Cancer (IARC), shift work involving night work is classified as a probable carcinogen (Group 2A) (IARC Monograph Volume 100, 2007, re-evaluated in 2010). Prevention relies on schedule design, medical surveillance, and worker support.

Definition

In Morocco, the Labor Code (Article 183) defines night work as work performed between 9:00 PM and 6:00 AM under the conditions stipulated by the law. This period may be adjusted by decree for certain sectors (continuous industries, transport, health, media, security).

Effects on Health

Night work disrupts circadian synchronization (the biological clock set to the day) and induces:

Sleep disorders: insomnia, daytime sleepiness, sleep fragmentation.
Chronic fatigue: decreased alertness, cognitive impairment, increased risk of error and accident.
Cardiovascular risks: hypertension, coronary heart disease.
Metabolic disorders: type 2 diabetes, obesity (dysregulation of blood glucose and leptin).
Cancer risks: IARC Group 2A classification (breast, prostate, colon — according to available epidemiological studies).
Psychosocial effects: isolation, depression, family difficulties.

Affected Populations

Night work primarily affects:

continuous industries (chemicals, steel, energy, food processing);
health (hospitals, emergencies);
transport (road, rail, air, maritime);
security, surveillance;
media, telecommunications, IT (24/7 support).

Prevention

Preventive measures include:

Schedule design: rapid rotations (2-3 days), rotation direction (morning → afternoon → night), limitation of consecutive night shifts.
Strategic breaks: short breaks every 2-3 hours, short nap in the middle of the night.
Lighting: high light intensity (≥ 500 lux) during the night to promote alertness (EN 12464-1 standard for workplace lighting).
Work environment: ergonomics, access to balanced meals, water, coffee.
Social and psychological support: access to an occupational physician, listening, information.
Duration limitation: no prolonged night work over several years for vulnerable workers (pregnant women, older workers, those with pathologies).

Regulation in Morocco

The Moroccan Labor Code (Law No. 65-99) imposes, via Article 183, a 50% increase in the hourly wage for night work. The night work of women and young workers is regulated. Enhanced medical surveillance (Title IV, Articles 304 to 343 — occupational medicine) is mandatory for night workers.

International Framework

At the international level, ILO Convention No. 171 (1990) on night work defines applicable principles: a maximum average of 8 hours per night, rest periods, medical surveillance, and possible transfer to a day post for health reasons. This convention is not universally ratified by all countries.

At the European level, Directive 2003/88/EC of 4 November 2003 (concerning the organisation of working time) imposes a minimum daily rest period of 11 consecutive hours and limits night work to an average of 8 hours per 24 hours.

Sources et références

Code du travail marocain (Loi n° 65-99), article 183 (travail de nuit) + Titre IV articles 304-343 (médecine du travail) ILO NATLEX : https://natlex.ilo.org/dyn/natlex2/r/natlex/fe/details?p3_isn=67319
INRS — Travail en horaires atypiques : Ce qu'il faut retenir (URL vérifiée 24/10/2026) https://www.inrs.fr/risques/travail-horaires-atypiques/ce-qu-il-faut-retenir.html
INRS — Travail en horaires atypiques : Démarche de prévention (URL vérifiée 24/10/2026) https://www.inrs.fr/risques/travail-horaires-atypiques/demarche-de-prevention.html