Summary: Pooled evidence indicates that shift workers perform worse than non-shift workers on tasks that measure attention, working memory, and information processing.
Source: BMJ
New pooled analyses show shift work is associated with reduced working memory and slower mental processing speed, according to a meta-analysis published in Occupational & Environmental Medicine.
Researchers found that shift work also corresponds with diminished alertness and visual attention, and with poorer impulse control and situational responses — factors that could increase the risk of workplace accidents and errors.
Shift work disrupts the body’s circadian rhythm by forcing activity and rest patterns that conflict with the natural light–dark cycle. That misalignment has been linked to sleep disorders, cardiovascular disease, obesity, diabetes, mood disorders, and substance misuse. Less clear until now was how shift work affects higher cognitive functions such as processing speed, working memory, and vigilance.
To clarify these effects, the research team systematically searched scientific databases for studies comparing cognitive performance in shift workers and non-shift workers among employed adults.
The analysis included 18 observational studies published between 2005 and 2020, totaling 18,802 participants with an average age of about 35. The studies assessed six cognitive domains using standardized tests: processing speed, working memory, psychomotor vigilance (alertness), cognitive control (impulse control and situational response), visual attention (ability to filter out irrelevant visual information), and task switching (automatic shifting between tasks).
Of the included studies, five compared fixed-shift workers with standard daytime workers, 11 compared rotating-shift workers with daytime workers, and two did not specify shift type. Roughly half of the studies focused on healthcare workers; the remainder examined other professions such as police officers and IT staff.
When results were pooled, shift workers performed significantly worse than non-shift workers on five of the six cognitive outcomes. The largest effect was observed for cognitive control (impulse control and situational response). Smaller but statistically significant effects were observed for processing speed, working memory, psychomotor vigilance, and visual attention. No consistent effect was found for task switching.
Biologically, working outside the normal day–night cycle disrupts the circadian system and alters hormone patterns such as cortisol and melatonin, which in turn disturb the sleep–wake cycle and can impair attention, memory, and reaction times.
The authors note important limitations. The studies used a wide range of cognitive tests and applied different definitions of shift work, which increases variability in the pooled estimates. Job demands and workloads vary across occupations, so the overall effect may overestimate or underestimate the impact in specific professions. Finally, most included studies were cross-sectional, limiting the ability to infer causality — it is not possible from these data alone to prove that shift work causes cognitive decline.
Despite these caveats, the pooled evidence suggests that reduced neurobehavioral performance among shift workers could contribute to higher rates of work-related injuries and errors, with clear implications for occupational health and safety.
The researchers recommend practical protective measures to reduce neurobehavioral decline in shift workers. Suggested countermeasures include scheduled naps, structured recovery plans, and regular monitoring of cognitive performance. They emphasize that as a more robust body of high-quality research becomes available, further meta-analyses should be conducted to design and validate targeted interventions that mitigate cognitive impairment associated with shift work.
About this neuroscience and memory research news
Author: Press Office
Source: BMJ
Contact: Press Office – BMJ
Image: The image is in the public domain
Original Research: Closed access.
“Neurocognitive impairment in night and shift workers: a meta-analysis of observational studies” by Thomas Vlasak et al., Occupational and Environmental Medicine
Abstract
Neurocognitive impairment in night and shift workers: a meta-analysis of observational studies
Objective
Shift work remains essential to modern economies, but its effects on neurobehavioral performance are debated. This meta-analysis aimed to summarize available evidence on how shift work relates to different cognitive functions in employed adults.
Methods
The authors searched multiple literature databases for studies up to April 2021 that compared shift workers with non-shift workers using neurobehavioral performance tests. A random-effects meta-analysis was conducted using Hedges’ g to estimate standardized mean differences, with sensitivity analyses (including funnel plots and meta-regressions) to assess heterogeneity and potential bias.
Results
Eighteen studies met inclusion criteria, providing data from 18,802 participants and 37 effect sizes across six cognitive domains. Compared with non-shift workers, shift workers showed worse performance in processing speed (g ≈ 0.16), working memory (g ≈ 0.28), psychomotor vigilance (g ≈ 0.21), cognitive control (g ≈ 0.86), and visual attention (g ≈ 0.19). Task switching did not show a consistent difference.
Conclusions
This meta-analysis provides evidence that shift work is associated with decreased cognitive performance in several domains, including processing speed, working memory, vigilance, cognitive control, and visual attention. Occupational health policies should consider protective strategies to reduce neurobehavioral impairment in shift workers, and further high-quality longitudinal research is needed to guide effective interventions.