Shift Work Impairs Cognitive Function

Megan Brooks

November 07, 2014

Shift work over a period of 10 or more years, and the disruption in circadian rhythm it causes, takes a toll on cognitive function, a new study shows.

"Shift work chronically impairs cognition, with potentially important safety consequences, not only for the individuals concerned but also for society," the authors say.

Their study shows that the harmful effects on the brain can be reversed when shift work ends, but it may take up to 5 years to achieve full recovery.

"While it is known that shift work is associated with chronic health complaints (eg, cardiovascular disease, metabolic syndrome, breast cancer and reproductive problems), very little was previously known about the long-term consequences of shift work on cognitive abilities," Philip Tucker, PhD, Psychology Department, College of Human and Health Sciences, Swansea University, United Kingdom, told Medscape Medical News.

"Our study shows that the long-term effects of shift work on the body clock are not only harmful to workers' physical health, but also affect their mental abilities," he said.

The study was published online November 3 in the journal Occupational and Environmental Medicine.

Brain Drain

The researchers tracked the cognitive abilities of 3119 employed and retired workers who were 32, 42, 52, and 62 years of age at their initial assessment, with 5-year and 10-year follow-up assessments. They are part of the Vieillissement et Santé au Travail (VISAT; Aging and Health at Work) study.

At each assessment, participants were given validated tests assessing global cognitive performance, memory, and processing speed. In all, 1197 participants were assessed at all time points. A total of 1484 had shift work experience (current or past) and 1635 did not.

The authors found that shift work was associated with a chronic impairment in cognitive function. The association was highly significant for exposures to rotating shift work lasting longer than 10 years. The cognitive loss was equal to 6.5 years of age-related decline, the researchers say.

Once participants retired from shift work, full cognitive recovery took up to 5 years.

"Our analyses suggest that the effects could not be attributed to poorer sleep quality among shift workers, which we know from previous studies has acute (i.e., short-term) effects on performance," Dr Tucker told Medscape Medical News. "Rather, it seems likely that our findings reflect the disruption of the shift workers' circadian rhythms, which has been shown by other researchers to have an impact on brain structures involved in cognition and mental health over the lifespan."

The findings have clear implications for healthcare providers, Dr Tucker said.

"Shift workers should receive regular health checks that include assessments of mental performance, especially those who have remained in shift work for more than 10 years," Dr Tucker said. "The cognitive impairment associated with shift work may have consequences for the safety of shift workers and the society that they serve, as well as for shift workers' quality of life. The findings highlight the potential benefits of arranging shift patterns in ways that minimize circadian disruption."

Daniel Hackam, PhD, from Western University, London, Ontario, Canada, who has studied shift work but wasn't involved in the current study, reviewed the results for Medscape Medical News.

"The results of this study are in line with the larger shift work literature," Dr Hackam said. "There is a pretty clear dose-response effect too."

The study had no commercial funding. The authors and Dr Hackam have disclosed no relevant financial relationships.

Occup Environ Med. Published online November 3, 2014. Abstract


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