Night and shift work: health risks, legal duties and shift design

· ClueFrame

Night work is not an organisational exception. Hospitals, transport, logistics, continuous-process plants, security services and retail function because someone works while others sleep. For the employer and the occupational physician this brings specific legal duties and a risk assessment that cannot stop at noise or manual handling.

How widespread it is

IARC estimates that around 20% of workers in North America, Europe and elsewhere are employed outside the standard daytime shift, with higher shares in manufacturing, healthcare, retail, services and transport.

The OSHwiki entry "Working time", maintained within EU-OSHA, reports that one fifth of workers in the EU-27, 21%, said they performed night work in 2021, based on Eurofound data. The same source notes that night work is more widespread among men than women (25% against 17%) and more frequent among self-employed workers and those on temporary contracts. The most exposed occupations include the armed forces, protective and security services, and health and care professions.

The IARC evaluation

In 2019 a working group meeting in Lyon from 4 to 11 June, made up of 27 experts from 16 countries, re-evaluated night shift work for the International Agency for Research on Cancer (IARC/WHO). The outcome is set out in Monographs Volume 124 "Night Shift Work", published in 2020, which updates the earlier Volume 98 of 2010.

Night shift work is classified as "probably carcinogenic to humans" (Group 2A). The classification rests on:

  • limited evidence in humans, with positive associations observed for cancers of the breast, prostate, colon and rectum;
  • sufficient evidence in experimental animals;
  • strong mechanistic evidence, including immunosuppression, chronic inflammation and cell proliferation.

Two clarifications are essential if this information is not to be misused. First: an IARC classification identifies a hazard, not a level of risk; it does not say how many cases are attributable or to which exposures. Second: the Agency does not issue regulatory recommendations. Translating Group 2A into company measures is the job of the employer, the prevention service and the occupational physician.

The hypothesised mechanisms

The mechanisms cited in the IARC evaluation as the basis of the strong mechanistic evidence are immunosuppression, chronic inflammation and cell proliferation. These are biologically plausible pathways through which the exposure may act, and they are consistent with the misalignment between the body's rhythms and the imposed working schedule.

Alongside this, night work affects safety more immediately: reduced and fragmented sleep, lower alertness in the middle hours of the night, greater difficulty with sustained vigilance tasks.

Italian legal definitions

Legislative Decree 66/2003 sets the operational definitions on which the duties are built.

The night period is a period of at least seven consecutive hours including the interval between midnight and five in the morning.

A night worker is:

  • someone who, as a normal matter, performs at least three hours of their daily working time during the night period; or
  • in the absence of collective bargaining rules, someone who performs night work for a minimum of eighty working days per year, a threshold reproportioned in the case of part-time work.

The distinction matters: night worker status triggers protections that do not apply to someone who works at night only occasionally.

On duration limits, the working time of night workers may not exceed eight hours on average in each twenty-four hours.

Health surveillance

Legislative Decree 66/2003 also provides that night workers undergo preventive and periodic fitness assessments, arranged and paid for by the employer, at intervals of at least every two years.

This duty is additional to, and does not replace, the general framework of Legislative Decree 81/2008, which requires the employer to assess all risks and entrusts health surveillance to the occupational physician. In practice, night work must be treated as a risk factor to be assessed in the risk assessment document, with measures following from it, and not merely as a contractual item.

Some operational points:

  • identify precisely who falls within the definition of night worker, distinguishing them from those on evening shifts;
  • document the actual frequency of assessments;
  • manage findings of unfitness for night work, and the resulting redeployments, in a traceable way;
  • coordinate the assessment with that of work-related stress, covered in preventing work-related stress.

On the role and limits of health surveillance, see health surveillance and the occupational physician.

Designing less harmful shift systems

The OSHwiki entry "Working time" cites the review by Bambra and colleagues covering 26 interventions on shift organisation. According to that work, the three most effective factors are:

  • fast rather than slow rotation, that is, few consecutive night shifts instead of long blocks;
  • forward rotation (morning-afternoon-night) rather than backward rotation;
  • self-scheduling of shifts by workers, meaning genuine control over their own hours.

These findings concern organisation, not individual behaviour: no leaflet on sleep hygiene compensates for a badly built shift plan.

Some concrete choices follow: limit consecutive night shifts, guarantee adequate rest after the last night, avoid shift changes at minimal notice, publish the roster well in advance, and provide a routine procedure for swapping shifts between colleagues.

A methodological caveat: the healthy worker effect

The same OSHwiki entry raises a problem to bear in mind when reading company data: the healthy worker effect. The good health observed in groups of older shift workers may be a selection artefact, because those who tolerate night work poorly tend to leave it or move off that job.

The practical consequence: if the shift workers in your company with twenty years of service are in good health, that is not proof the shift system is sound. You also need to look at those who stopped, and why. The theme intersects with workforce ageing, covered in intergenerational team building and safety.

Information and training for shift workers

One final, often neglected point. Training for shift workers almost always fails for logistical rather than educational reasons: sessions scheduled at the end of a night shift, training rooms accessible only during the day, content delivered when attention is at its lowest.

Some measures:

  • schedule sessions at the start of the shift, not at the end;
  • replicate the same content across all shifts, instead of concentrating it on the most convenient one;
  • count training time as working time, always;
  • use short, repeated formats with spaced learning checks;
  • address sleep, eating during the night and return after the rest period explicitly, without shifting responsibility for the organisation onto the worker.

Night work cannot be eliminated in many sectors. It can, however, be designed, measured and monitored with the same rigour applied to any other risk factor.