People who work night shifts may face a significantly higher risk of developing long COVID, according to a study published last week in the Scandinavian Journal of Work, Environment & Health. That risk may rise even further among night shift workers who also have chronic insomnia.
For the study, researchers led by a team from the Medical University of Vienna and ISGlobal followed participants in the COVICAT study who had COVID-19. COVICAT is a large prospective epidemiologic project in Spain that tracked thousands of volunteers from 2021 through 2023 to evaluate the impacts of the COVID pandemic.
Night shift work and sleep habits were assessed in 2021. Long COVID was defined as symptoms persisting for at least three months following COVID infection.
Neurologic symptoms most common
Of the 1,899 participants during the two-year follow-up after infection, 283 (14.9%) developed long COVID. Most infections occurred when Omicron was the dominant variant, and most initial cases were mild or moderate. Neurologic symptoms were the most common, reported by 54.4% of participants with long COVID, followed by muscular symptoms (30.4%) and respiratory symptoms (20.5%).
After adjusting for potential confounding factors, the researchers found that night shift workers were 88% more likely to develop long COVID than day workers (risk ratio [RR], 1.88). The association was stronger among people who worked more night shifts.
Those working at least three nights per month had more than twice the risk of long COVID (RR, 2.07). A similar increase was seen among participants who had worked nights for at least three months (RR, 2.07).
At the same time, night shift work was not associated with a greater likelihood of COVID infection, suggesting that circadian upheaval may affect how the body recovers from infection more than how susceptible the body is to becoming infected.
“Our findings suggest that circadian disruption plays a role in the transition from acute infection to persistent symptoms,” ISGlobal researcher and study coauthor Manolis Kogevinas, PhD, said in an ISGlobal news release.
The association between night work and long COVID was particularly pronounced among participants with obesity, who had nearly three times the risk of long COVID (RR, 3.77) than day workers without obesity (RR, 1.28). While night shift work and obesity have been independently associated with markedly higher COVID risk, write the researchers, the current findings involved a small number of participants, so “the observed associations should be interpreted with caution and require replication.”
Poor sleep might play a role
Insufficient and/or poor-quality sleep also emerged as a separate risk factor. Participants with chronic insomnia, which the researchers defined as sleep problems lasting more than three months and occurring at least three nights per week, had a 42% higher risk of long COVID than those without chronic insomnia (RR, 1.42).
The combination of night work and chronic insomnia carried an even higher risk. Participants who experienced both had 2.69 times the risk of long COVID compared with day workers without chronic insomnia.
Our findings indicate that night work and poor sleep are independently and jointly associated with long-COVID risk.
“Our findings indicate that night work and poor sleep are independently and jointly associated with long-COVID risk, highlighting a potential role for circadian and sleep disruption in the progression from acute infection to persistent post-infectious sequelae,” write the researchers.
The authors suggest modifiable factors could reduce the risk of long COVID. “Promoting healthy sleep habits and minimising circadian disruption could represent simple, low-cost strategies to reduce the long-term consequences of viral infections, particularly among people who work night shifts,” concludes Kogevinas.
The authors said they believe the findings are the first to link night shift work to an increased risk of long COVID.
