Summary: Pooled data reveals shift workers perform worse on tasks associated with attention, working memory, and information processing than non-shift workers.
Shift work is linked to poorer working memory and slower mental processing speed, finds a pooled data analysis of the available evidence, published online in Occupational & Environmental Medicine.
It is also associated with lower levels of alertness and visual focus, and the ability to control impulses and situational response, potentially heightening the risk of workplace injuries and errors, suggest the researchers.
Shift work has been linked to serious health issues as a result of the internal body clock (circadian rhythm) being out of step with the normal light-dark cycle. These include sleep disorders, cardiovascular disease, obesity, diabetes, mood disorders, and substance abuse.
But its potential impact on higher brain function, such as mental processing speed and working memory, isn’t clear.
In a bid to resolve these uncertainties, the researchers scoured research databases for studies looking at the impact of shift work on cognitive performance in working adults.
In all, 18 studies, published between 2005 and 2020, involving 18,802 participants (average age 35) and covering six different outcomes measured by formal tests, were included.
The outcomes were: processing speed; working memory; alertness (psychomotor vigilance); impulse control and situational response (cognitive control); ability to filter out unimportant visual cues (visual attention); and ability to unconsciously shift between tasks (task switching).
Five of the studies compared workers in fixed shifts with those working normal office hours while 11 compared workers in rotating shifts with those working normal office hours. Two studies didn’t specify shift type.
Half the studies included healthcare professionals while the other half focused on different professions, such as police officers, IT staff, etc.
The results of the studies were pooled, indicating significantly worse performance in shift workers than other types of workers for five of the six outcomes assessed.
A large significant effect was seen for impulse control and situational response, while the effect for processing speed, working memory, alertness and ability to filter out unimportant visual clues was significant but small. No effect was seen for task switching.
Working outside the normal day-night cycle interferes with the circadian rhythm and the expression of the hormones that govern it–cortisol and melatonin—which in turn disrupts the sleep-wake cycle, explain the researchers.
Although this is the first pooled data analysis to look at the impact of shift work on different aspects of brain function among working adults, the researchers acknowledge certain limitations to their findings.
These include the wide variety of tests used to assess cognitive performance and differing definitions of shift work in the included studies.
And because jobs differ in terms of demands and workloads, the results might over- or underestimate the impact of shift work in specific types of profession, they caution. And since the included studies were of cross-sectional design, it’s not possible to conclude that shift work does impair higher brain function performance, they add.
“Reduced neurobehavioural performance in shift workers might play an important role regarding work-related injuries and errors,” with implications for workplace health and safety, write the researchers.
They conclude: “Protective countermeasures (eg: naps, recovery plans, regular monitoring) for reduction in neurobehavioural performance of shift workers should be promoted to minimize the risk of adverse health and work-related outcomes.
“When a more consistent body of high-quality literature is available, we highly recommend replication of analysis to develop practical interventions to overcome neurobehavioural impairment.”
About this neuroscience and memory research news
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Neurocognitive impairment in night and shift workers: a meta-analysis of observational studies
Shift work is an essential element of modern labour, ensuring ideal conditions of service for today’s economy and society. Despite the beneficial properties, its impact on the neurobehavioural performance of exposed subjects remains controversial. This meta-analysis aimed to provide the first summarising effects regarding the association between shift work exposure and different cognitive functions.
A literature search was performed using the databases PubMed, PsyINFO, PsyARTICLES, MedLine, PsycNET and Scopus including eligible studies up to April 2021 that compared shift workers with non-shift workers regarding neurobehavioural performance tests. We carried out a random-effects model using Hedges’ g as a meta-analytical effect size with a restricted likelihood estimator to summarise the mean differences between the exposure group and controls. Positive effect sizes indicate higher performance for non-shift workers. The heterogeneity of effect sizes was addressed by sensitivity analysis using funnel plots, Egger’s tests, p-curve analysis, meta-regressions and subgroup analysis.
We included 18 studies resulting in a total sample of 18 802 participants and 37 effect sizes concerning six different neurobehavioural outcomes. Our results showed significantly worse performance in shift workers compared with non-shift workers in the following cognitive functions with g (95% CI): processing speed 0.16 (0.02 to 0.30), working memory 0.28 (0.51 to 0.50), psychomotor vigilance 0.21 (0.05 to 0.37), cognitive control 0.86 (0.45 to 1.27) and visual attention 0.19 (0.11 to 0.26).
We provide the first meta-analytical findings that associate shift work with decreased cognitive performance in processing speed, working memory, psychomotor vigilance, cognitive control and visual attention.