Shift work is linked to weaker working memory and slower mental processing speed, finds a pooled data analysis of available evidence, published online in Occupational and environmental medicine.

It is also associated with lower levels of alertness and visual concentration, and the ability to control impulses and situational response, potentially increasing the risk of injuries and errors on the job, the researchers suggest.

Shift work has been linked to serious health problems due to the internal biological 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 functions, such as mental processing speed and working memory, is unclear.

In an effort to resolve these uncertainties, the researchers scoured research databases for studies examining the impact of shift work on cognitive performance in working adults.

A total of 18 studies, published between 2005 and 2020, involving 18,802 participants (mean age 35 years) and covering six different outcomes measured by formal tests, were included.

The results were: processing speed; working memory; alertness (psychomotor alertness); impulse control and situational response (cognitive control); ability to filter out unimportant visual cues (visual attention); and the ability to switch unconsciously from one task to another (task switching).

Five of the studies compared fixed shift workers with those working regular office hours, while 11 compared rotating shift workers with those working regular office hours. Two studies did not specify the type of shift.

Half of the studies included medical professionals while the other half focused on different professions, such as police officers, IT personnel, etc.

The results of the studies were pooled, indicating significantly lower performance among shift workers compared to 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 the ability to filter out unimportant visual cues was significant but small. No effect was observed 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 disrupt the sleep-wake cycle, the researchers explain.

Although this is the first pooled data analysis to examine the impact of shift work on different aspects of brain function in working adults, the researchers recognize some limitations to their findings.

These include the wide variety of tests used to assess cognitive performance and the differing definitions of shift work in the included studies.

And because jobs differ in terms of demands and workloads, the results could overestimate or underestimate the impact of shiftwork in specific occupation types, they warn. And because the included studies were cross-sectional in design, it is not possible to conclude that shift work impairs performance of higher brain functions, they add.

“Reduced neurobehavioral performance in shift workers may play an important role in relation to work-related injuries and errors,” with implications for occupational health and safety, the researchers write.

They conclude: “Protective countermeasures (e.g. naps, recovery plans, regular monitoring) to reduce the neurobehavioral performance of shift workers should be encouraged to minimize the risk of adverse health and work-related outcomes.

“When a more consistent body of high-quality literature is available, we strongly recommend replication of the analysis to develop practical interventions to overcome neurobehavioral disorders.”


Journal reference:

Vlasak, T. et al. (2022) Neurocognitive impairment in night and shift workers: a meta-analysis of observational studies. Occupational and environmental medicine.