Night shifts and chronic insomnia may increase long COVID risk

The first evidence that night work and chronic insomnia may increase the risk of developing long COVID comes from a new study led by ISGlobal, a centre supported by "la Caixa" Foundation, in collaboration with the Germans Trias i Pujol Research Institute (IGTP), through the GCAT | Genomes for Life cohort. The findings, published in the Scandinavian Journal of Work, Environment and Health, highlight the importance of healthy sleep habits in preventing long COVID and other post-acute infectious syndromes.

Studies in humans show that disrupting the body's internal clock can weaken immune responses and increase susceptibility to infections. During the COVID-19 pandemic, a study in UK found that sleep disturbances were linked to a higher risk of SARS-CoV-2 infection. "However, no previous study had evaluated whether disrupting the body's biological clock also increases the risk of developing long COVID", says first author Kyriaki Papantoniou, Associate Professor at the Medical University of Vienna and Associated Researcher at ISGlobal. 

Night shift workers at increased risk of long COVID

In this study, the research team followed 2,941 adults in the population-based COVICAT cohort in Catalonia between 2021 and 2023. Among the 1,899 participants who became infected with SARS-CoV-2, 284 developed long COVID - defined as having persistent symptoms lasting for more than three months after the infection - during the 2-year follow-up.

Compared with day workers, those working night shifts had an 88% higher risk (i.e. almost double) of developing long COVID after accounting for other risk factors such as vaccination history or chronic diseases. This association was stronger in night workers with obesity. Moreover, the increased risk was observed both in current and former night workers, suggesting that it reflects longer-term effects of circadian disruption rather than short-term changes.

In contrast, night shift work was not associated with a higher risk of becoming infected, suggesting that disruption of the biological clock may influence how the body recovers from infection rather than the likelihood of catching the virus.

"Our findings suggest that circadian disruption plays a role in the transition from acute infection to persistent symptoms," says ISGlobal researcher Manolis Kogevinas, who coordinated the study.

Poor sleep further amplifies the risk

The researchers found that chronic insomnia also increased the risk of long COVID by 42%, independently of night shift work. Together, the two factors had a synergistic effect: night shift workers with chronic insomnia were 2.7 times more likely to develop long COVID than day workers without insomnia.

The biological mechanisms involved are not yet fully understood, but the time of day when the body encounters a pathogen may influence the immune response. In addition, disruption of the body's biological clock can impair the immune system's ability to clear the infection. 

Improving sleep as a preventive strategy

Given the increase of insomnia prevalence in the general population, the authors underline the need to understand the short and long-term effects of disturbed sleep on infection-related outcomes. In any case, the findings point to sleep as a potentially modifiable factor in preventing long COVID and other post-infectious conditions.

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."

Manolis Kogevinas, ISGlobal researcher

The researchers note that the study's strengths include the use of a well-characterised population-based cohort with detailed information on work schedules, sleep habits and health, as well as an internationally recognised definition of long COVID. However, the participants were aged 40 to 65 years, so the findings may not necessarily apply to younger or older populations, and other occupational factors, such as work-related stress, cannot be completely ruled out.