Shift Work Linked to Higher Risk of COVID-19 Hospitalisation

Peter Russell

April 27, 2021

Working unsociable hours could increase the risk of being hospitalised with COVID-19 by up to three times compared with people who work regular hours, researchers said.

The study, published in the journal Thorax,  suggested that shift work could be as important a risk factor as other known high-risk characteristics such as ethnic background and social deprivation, researchers said.

They concluded that additional precautions in the workplace, as well as vaccination against COVID-19, could mitigate some of the extra risks.

Previous studies have found adverse health effects of shift work, such as respiratory disease, diabetes, cancer, and non-Covid-19 infectious diseases. Although the mechanisms underlying these associations remain uncertain, one hypothesis is that irregular working hours could lead to circadian misalignment.

So, the researchers set out to investigate whether disruption of the circadian clock increased susceptibility to COVID-19.

Unsociable Working Hours

"We defined shift work as if you work outside the hours of 9am to 5pm," said Dr John Blaikley, a Medical Research Council clinician, who led the study.

"Between 10% and 40% of the country's population do some type of shift work," he told Medscape News UK.

The researchers based their findings on data from the UK Biobank. Of the 502,450 participants enrolled, 6442 were tested for COVID in hospital, resulting in 498 positive tests between March and August 2020. In those that had positive tests, 316 did not work shifts, 98 worked irregular shifts, and 84 worked permanent shifts.

The study was based on 284,027 participants aged 40 to 69 when they enrolled in the UK Biobank, after those in part-time work and individuals who did not reveal their employment status were excluded.

The data was linked to other resources, such as hospital and GP records.

COVID Risks Remained High Despite Other Factors

People who worked irregular shifts were 2.4 times more likely to test positive for COVID-19 in hospital than those who did not work irregular hours. That increased to 2.5 times a higher risk for permanent shift workers.

Permanent night-shift workers had a 2.49 higher risk, rising to more than three times the risk for irregular night shift workers.

In an analysis of job sector types and COVID-19, healthcare shift workers had a 2.53 higher risk of being hospitalised with COVID.

The higher risks were seen to persist after other factors were taken into account, such as sleep duration, BMI, alcohol consumption, and smoking status.

The researchers also carried out an analysis on a subset of biobank participants whose occupational shift work status was updated in 2017.

In the cohort, 43,878 participants were used to analyse the effect of shift work with 72 participants being hospitalised for COVID-19. From this analysis shift workers were 4.5 times more likely to test positive for COVID-19.

"We don't quite know yet how the adverse effects are being driven," said Dr Blaikley. "It could be environmental factors, such as less cleaning in the workplace, or increasing tiredness." It could also be linked with irregularities in the internal body clock, some of which "does affect the immune response".

Dr Hannah Durrington, a MRC clinician scientist at the university, who co-authored the paper, added: "We do believe it should be possible to substantially mitigate these risks through good handwashing, use of face protection, appropriate spacing, and vaccination."

The authors stressed that they carried out an observational study so were unable to establish cause and effect. However, they said a strength of the study was the large number of people involved.

Shift work is associated with positive COVID-19 status in hospitalised patients doi:10.1136/thoraxjnl-2020-216651, Thorax.


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