New research shows shift work outside the 9-5 can have a big impact on the brain. 

The new analysis re-confirms previous findings that shift work is linked to poorer working memory and slower mental processing speed. 

Overnight and early morning shifts were also associated with lower levels of alertness and visual focus, and the ability to control impulses and situational response. The researchers say this could heighten the risk of workplace injuries and errors.

Many of the issues stem from 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 studies now suggest there is an impact on higher brain function, such as mental processing speed and working memory too. 

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.

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.

“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 minimise 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.”

The study is accessible here.