Shift work is becoming an increasing part of the working patterns of Americans, but some people deal with these irregular schedules better than others. Now, a new study suggests the ability to cope with shift work may be down to genetics.

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Researchers identified a gene variant that is more common among shift workers with job-related exhaustion.

In the United States, around 15 percent of full-time employees work shifts – that is, they work outside of the standard 9-5 schedule.

According to the National Sleep Foundation, around 37 percent of shift workers fail to get enough sleep as a result of their work schedule, and around 10 percent of night and rotating shift workers experience sleep disorders – such as insomnia or daytime fatigue.

These disorders are thought to arise from the disruption shift work causes to the body’s circadian rhythm – the approximate 24-hour cycle of physical, mental, and behavioral changes that mainly respond to light and darkness.

However, precisely why some people develop sleep disorders and job exhaustion as a result of shift work while others do not has been unclear.

Prof. Tiina Paunio, of the University of Helsinki in Finland, and her team sought to determine whether there might be a genetic explanation for this discrepancy.

For their study – published in the journal Sleep – the researchers analyzed the genomes of shift workers who were part of the Health 2000 Survey – a nationally representative survey conducted between 2000-2011, involving more than 8,000 individuals aged 30 and older residing in mainland Finland.

As part of the survey, respondents were required to report their experiences of job-related exhaustion and fatigue.

From their analysis, Prof. Paunio and team discovered a variation near the melatonin receptor 1A (MTNR1A) gene that was more common among shift works who reported exhaustion relating to their job.

Further investigation revealed that the variation near the MTNR1A gene is likely associated with a reduction in the number of melatonin receptors, caused by changes to DNA methylation that weaken MTNR1A gene expression.

Melatonin is a hormone that is released into the blood in response to darkness, telling us when it is time to sleep. A reduction in the number of melatonin receptors leads to a decrease in melatonin signaling, which disrupts the circadian rhythm.

As such, the researchers hypothesize that the MTNR1A gene variation uncovered in their study may partly explain why some shift workers find it difficult to cope with an irregular work schedule.

The authors write:

“These findings suggest that a variant near MTNR1A may be associated with job-related exhaustion in shift workers. The risk variant may exert its effect via epigenetic mechanisms, potentially leading to reduced melatonin signaling in the brain. These results could indicate a link between melatonin signaling, a key circadian regulatory mechanism, and tolerance to shift work.”

However, Prof. Paunio offers a word of caution when interpreting the findings.

“The variant we have now discovered can only explain a small part of the variation between individuals, and it cannot be used as a basis to determine a person’s tolerance to shift work,” she says.

Read about a study that suggests night shift work does not raise breast cancer risk.