This article was originally published in German on Medscape.
Shift work is associated with poor working memory and slower mental processing speed. This is the outcome of a meta-analysis of pooled data published online March 8 in Occupational & Environmental Medicine.
Because of its cognitive effects, shift work can increase the risk of injuries and mistakes in the workplace. Therefore, protective measures such as regular breaks and vigilance checks should be encouraged, suggest author Thomas Vlasak, PhD, a researcher at the Sigmund Freud University in Linz, Austria, and colleagues.
A total of 18 studies published from 2005-2020 were included in the analysis. The studies included 18,800 subjects (average age, 35 years) and examined the following six outcomes, all measured through formal tests:
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Impulse control and situational reaction (cognitive control)
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Working speed
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Working memory
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Awareness (psychomotor vigilance)
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The ability to filter out unimportant visual information (visual awareness)
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The ability to unconsciously switch between different tasks (task switching).
Significantly Worse Performance
The results of the different studies showed that shift workers performed significantly worse, compared with other workers, in five of the six outcomes investigated.
A major, statistically significant effect was found for impulse control and situational reaction, whereas the effects for working speed, working memory, awareness, and the ability to filter out unimportant visual information were statistically significant, but smaller. Task switching was the only outcome that saw no negative effect.
The results showed a significantly poorer performance by shift workers, compared to nonshift workers, in the following cognitive functions, with a decrease in memory span:
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Working speed by 0.16 (95% CI, 0.02 – 0.30)
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Working memory by 0.28 (95% CI, 0.51 – 0.50)
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Psychomotor vigilance by 0.21 (95% CI, 0.05 – 0.37)
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Cognitive control by 0.86 (95% CI, 0.45 – 1.27)
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Visual awareness by 0.19 (95% CI, 0.11 – 0.26).
First Large Meta-Analysis
Working outside of the normal day-night cycle disrupts the circadian rhythm and the expression of hormones that control it (such as cortisol and melatonin), which in turn interrupts the sleep-wake cycle. This interruption leads to sleep disorders, cardiovascular diseases, obesity, diabetes, mood disorders, and drug abuse.
However, the possible effects on higher brain functions, such as mental processing speed and working memory, were previously unclear. Therefore, the researchers searched through six psychological and general medical databases for studies that investigated the effects of shift work on the cognitive performance of working adults.
According to the authors, this is the first pooled data analysis to examine the effects of shift work on various aspects of brain function in working adults.
In five of the studies, workers were in fixed shifts, and in 11 studies they were in rotating shifts. In each case, shift workers were compared with workers who worked normal office hours. Two studies did not contain any information on the type of shift.
Half of the studies included healthcare workers and half involved other occupational groups such as police officers and IT technicians.
Study Limitations
The researchers acknowledged certain limitations to their results. Since the workplaces differ with respect to requirements and workload, the results may overestimate or underestimate the effects of shift work in certain occupational groups.
Moreover, because the data are cross-sectional, it is not possible to draw the conclusion that shift work negatively impacts higher brain function, they add.
In addition, there is a large variety of tests used to assess cognitive performance, and the included studies used different definitions of “shift work.”
“As soon as a consistent corpus of high-quality literature is available, we urgently recommend that these analyses be replicated to develop practical interventions for overcoming neurological behavior disorders,” said co-author Alfred Barth, PhD, also from Sigmund Freud University.
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