Shift Work May Actually Hurt Your Ability To Think

Worker health depends on not just quantity, but timing of hours too.
A new study links shift work of any kind to poorer cognitive functioning.
Wavebreakmedia Ltd via Getty Images
A new study links shift work of any kind to poorer cognitive functioning.

When the Labor Department announced earlier this week it will extend overtime protections to millions of additional workers starting Dec. 1, advocates applauded. But a growing group of researchers is calling attention to a separate concern that affects many workers in the same group: In addition to how long employees work, worker health depends on when those hours are worked.

A new study links shift work to poorer cognitive functioning, finding that workers who reported having irregular shift schedules performed poorly on a test that measures cognitive decline, compared to those who had never or not recently performed shift work.

The test used in the study forces the brain to process conflicting information, said study co-author Christian Benedict, an associate professor in the Department of Neuroscience at Uppsala University, noting that processing conflicting information "appears highly relevant in stressful job-related situations.”

The bottom line is not good for shift workers. This research joins a host of other studies that document the ways working irregular shifts harms health, including raising the risk of diabetes, obesity, some cancers, workplace injury and heart disease. Some findings show that women may be even more vulnerable to these effects.

Considering a large proportion of today’s workforce performs shift work -- approximately 15 million Americans, according to data from the Bureau of Labor Statistics -- the findings are troublesome, Benedict said.

Shift workers performed worse on executive functioning tests

The study, published earlier this week in the journal Neurobiology of Aging, included 7,143 workers. According to their self-reported work histories, 4,611 had never performed shift work, 1,531 performed shift work more than five years prior, 358 performed shift work within the past five years and 643 were currently working shifts. Everyone in the study completed the trail-making test, a challenge neurologists frequently use to measure cognitive processing speed and executive function in order to assess cognitive impairment. Performance on the test is measured by how long it takes a person to connect a series of numbers in ascending order.

Current and recent (within five years) shift workers took four seconds longer on average to complete the more demanding portion of the test that measured executive function -- approximately 60 versus 56 seconds, compared with those who had never performed shift work and those who hadn't done it for five years or more. Those results account for any other factors that might influence how someone performed on the test, like age, gender, educational status, physical activity level, perceived stress, sleep duration and cumulative sleep disturbance score.

The researchers did not specifically measure brain activity in one region versus another for this study, but Benedict explained the findings are interesting because previous research has shown the executive function portion of the test involves the frontal lobe of the brain, and that type of brain activity is the type that is known to decrease with age.

Disturbed circadian rhythm to blame

The problems with shift work stem from circadian misalignment -- i.e. sleeping, working, eating and being awake at the wrong times according to your body clock. Such misalignment can wreak havoc on health over time, sleep expert Charmane Eastman, a professor in the behavioral sciences department at Rush University Medical Center in Chicago, previously told The Huffington Post.

Studies in shift workers have shown that this internal body shifting may affect metabolism in ways that subsequently increase the risk of cardiovascular disease, as well as change levels of various hormones involved in brain function, which some research suggests might explain why memory problems and cognitive decline are associated with shift work.

“It’s another one of hundreds of studies showing that night shift work is bad for your health and performance.”

- Charmane Eastman, a professor in the behavioral sciences department at Rush University Medical Center in Chicago

The findings from this study are therefore not at all surprising, said Eastman, who was not involved in this recent study but noted that it's "another one of hundreds" that show shift work -- particularly night shift work -- has a negative impact on health and performance. "No surprises here," she said.

Eastman said she was surprised that this study showed that former shift workers of more than five years before the study had scores that were actually better than those of current and recent former shift workers -- and more in line with the individuals that had never performed shift work.

“That’s good news,” she said. “This may not be true for all impairments from night work.”

Typically, off-hours shifts that least disrupt sleep --for example, those that end around 11 p.m. or 1 a.m. -- tend to be the least harmful to health, she said. “People tend to get the most sleep with those shifts.”

If you do work overnights, don’t panic

First of all, in terms of cognitive decline, it was good news that time seemed to somewhat mitigate the cognitive decline. This suggests that it might actually be possible to recover somewhat from that negative outcome, Benedict said.

The research also demonstrates the importance of conducting additional studies to evaluate if other lifestyle modifications may help counter some of the worst effects of messing with circadian rhythms.

“Given that workers with irregular shift schedules represent an indispensable group of the workforce in our 24/7 society, we need interventional studies to examine if adherence to a healthy lifestyle (regular physical activity, improved sleep hygiene, healthy dietary patterns, not smoking and moderate alcohol consumption) can attenuate effects of shift work on general health, including that of the brain,” he explained.

Eastman added that for those working overnights, it can be possible to adapt your circadian rhythm, but it takes a lot of planning. For someone working until 6 or 7 a.m., it typically would require going to bed as soon as possible after work, wearing sunglasses when leaving work to avoid bright light in the morning before sleep, and getting bright light during the night shift, especially between midnight and 4 a.m. And that worker would also want to sleep late on days off as well, until around noon, essentially giving up morning activities, Eastman said.

The National Institute for Occupational Safety and Health has also weighed in on the topic, launching an online training program for nurses to increase their knowledge of behaviors that reduce the risks associated with shift work and long hours.

Sarah DiGiulio is The Huffington Post’s sleep reporter. You can contact her at


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