Daylight Saving Time: What Does It Mean for Workers' Health?

This article was originally published in Spanish in El País.

[It was co-authored by Manolis Kogevinas, emeritus professor of environmental epidemiology at the Barcelona Institute for Global Health (ISGlobal), Victòria Olivé, Occupational Health coordinator at Hospital Clínic de Barcelona, and José María Ramada Rodilla, head of the Occupational Health Service at Hospital del Mar de Barcelona and professor at Pompeu Fabra University.]

Every spring and autumn, millions of Europeans set their clocks forward or back by one hour. It is often claimed that these changes harm sleep, health, and workplace safety. But should we evaluate only their immediate effects, or also the consequences of how we organize our activities in relation to natural light?

The balance of daylight saving time's effects on health is not entirely clear. In fact, maintaining seasonal changes could be beneficial in the long term. Our biological clock regulates sleep, alertness, and numerous physiological functions, and natural light is its main synchronizing signal. Seasonal time shifts allow us to take advantage of more evening daylight in summer without excessively delaying sunrise in winter.

The balance of daylight saving time's effects on health is not entirely clear. In fact, maintaining seasonal changes could be beneficial in the long term.

But what happens if we focus on occupational health? It is true that clock changes can temporarily disrupt sleep and attention, especially in spring when we lose an hour. A review published in 2026 in the European Journal of Epidemiology, which analyzed 157 studies, found some immediate adverse effects, particularly regarding traffic accidents and certain cardiovascular events. However, the results are heterogeneous and do not indicate widespread harmful effects. The review also identified potential beneficial effects.

For workers, it is useful to distinguish three issues: accidents in the days following the change, what happens during the night shift when the clock is modified, and the risks of regularly working at night.

Do workplace accidents increase?

A common explanation is that getting less sleep after the spring clock change reduces attention and increases accidents. Some studies support this: one conducted in Italy observed approximately 2% more workplace accidents during the following three days, whereas after the autumn change it recorded a reduction of over 10%. However, other studies have not confirmed this increase, and overall, the evidence remains inconsistent.

The recent European review found some indications of a reduction in workplace accidents after the autumn change, but no consistent increase in spring. Therefore, although the mechanism is plausible, we cannot assert that clock changes systematically increase occupational accidents. When differences are observed, they appear to be transient.

What happens to those working that night?

Consider a nurse or an industrial worker on a 10:00 PM to 6:00 AM shift. In autumn, when the clocks are turned back, that shift can last nine actual hours; in spring, seven. Companies can adjust schedules to maintain the usual eight hours, but they do not always do so.

The extra hour in autumn can increase fatigue and reduce focus near the end of the shift, although we lack sufficient studies to quantify the added risk. Furthermore, the consequences depend on the task: a loss of focus does not mean the same in a routine task as it does when driving, operating machinery, or attending to a medical emergency. Additionally, compensation for the extra hour must be agreed upon—taking into account the annual calculation of working hours—as well as the corresponding rest period.

The underlying issue: regularly working night shifts

The clock change reminds us of a much more significant occupational health problem. Hospitals, transportation, and numerous services require night personnel. However, working repeatedly during the biological night can disrupt circadian rhythms, impair rest, and contribute to chronic diseases. A review of studies estimated a 36% higher risk of workplace injuries during night shifts compared to morning shifts.

The International Agency for Research on Cancer of the World Health Organization classified night shift work as probably carcinogenic to humans, research to which our teams contributed. In the MCC-Spain study, involving thousands of participants across different Spanish regions, we observed associations between night work and an increased risk of breast and prostate cancer, particularly in specific groups with long-term exposure. In complementary research, we examined the biological mechanisms in day- and night-shift workers. We detected significant changes in the timing of melatonin production—the so-called sleep hormone—and sex hormones, demonstrating how night work can alter physiological processes potentially linked to chronic diseases. These findings are not yet sufficiently reflected in preventive practices.

We should not confuse these repeated exposures over years with the minor shift that occurs twice a year. Their intensity, duration, and potential consequences are vastly different.

What can we do?

Measures should be proportionate and adapted to each sector. It does not seem necessary to impose uniform solutions for the clock change. Companies and workers can agree on adjustments to avoid the extra hour in autumn or, when that is not possible, ensure adequate compensation and sufficient rest. For tasks that are particularly sensitive to fatigue, additional breaks and a better distribution of the most demanding tasks can be helpful.

The main occupational health issue is not changing the clock twice a year, but working against our biological clock night after night.

The priority, however, is to better organize regular night work: limit consecutive night shifts, ensure sufficient rest between workdays, and properly manage light exposure. Prevention must be built into work organization, rather than relying solely on individual adaptation. Health surveillance should detect sleep disorders, persistent fatigue, and shift adaptation difficulties early on. Income loss should also be avoided when changing job roles or shifts is necessary for health reasons, and early retirement should be evaluated in justified cases.

The debate over keeping or abolishing seasonal time changes is legitimate and requires considering both immediate effects and the distribution of natural light throughout the year, along with its potential long-term benefits. But we should not exaggerate the risks of moving the clock by one hour while overlooking a far greater challenge. The main occupational health issue is not changing the clock twice a year, but working against our biological clock night after night.