A population-based study from the Barcelona Institute for Global Health (ISGlobal), conducted in collaboration with the Germans Trias i Pujol Research Institute, has identified night-shift work and chronic insomnia as potential risk factors for developing long COVID. The research, based on participants in Catalonia’s COVICAT cohort, provides the first reported evidence that disruption of the body’s circadian system may influence how people recover from SARS-CoV-2 infection. The findings suggest that sleep and work schedules could affect the transition from an acute viral illness to persistent symptoms lasting months after the initial infection.
The study followed 2,941 adults between 2021 and 2023. Of these participants, 1,899 became infected with SARS-CoV-2 during the two-year follow-up period, and 284 subsequently developed long COVID. The researchers defined long COVID as persistent symptoms continuing for more than three months after infection, in line with internationally recognised clinical definitions. The participants were between 40 and 65 years old and provided detailed information about their employment schedules, sleep patterns, vaccination history, chronic diseases and other health-related factors.
After adjusting for potential confounders, participants who worked night shifts had an 88 percent higher risk of developing long COVID than people who worked during the day. The association remained after accounting for factors including vaccination status and pre-existing chronic conditions. The elevated risk was particularly pronounced among night workers with obesity, suggesting that metabolic health may interact with circadian disruption and influence post-viral recovery.
Importantly, night work was not associated with a higher likelihood of becoming infected with SARS-CoV-2. This distinction indicates that circadian disruption may not primarily increase exposure to the virus or reduce initial resistance to infection. Instead, it may affect the biological processes that follow infection, including immune regulation, inflammatory control and the clearance of viral material. The increased risk was observed among both current and former night-shift workers, supporting the possibility that long-term alterations in circadian biology, rather than only temporary schedule changes, may be involved.
The circadian system is an internal timing network that coordinates sleep, hormone release, body temperature, metabolism and immune activity across the approximately 24-hour day. Light exposure, meal timing and work schedules help synchronise this system. Night work can force individuals to remain awake and active when the body is biologically programmed for rest, while sleeping during daylight can reduce the quality and duration of sleep. Experimental and human studies have shown that such misalignment can alter immune-cell activity, inflammatory signalling and the production of hormones such as melatonin and cortisol.
The researchers also found that chronic insomnia independently increased the risk of long COVID by 42 percent. The combination of night work and persistent insomnia was associated with the greatest risk: night-shift workers with chronic insomnia were 2.7 times more likely to develop long COVID than daytime workers who did not report insomnia. The interaction suggests that circadian misalignment and poor sleep may reinforce one another, potentially producing a stronger effect on immune recovery than either factor alone.
Several mechanisms could explain the findings, although the study does not establish a direct biological cause. The timing of viral exposure may influence the intensity and organisation of the immune response, because immune cells and inflammatory pathways follow daily rhythms. Circadian disruption may also impair the body’s ability to eliminate infection efficiently, prolong inflammatory activity or interfere with tissue repair. Chronic insomnia can further affect immune signalling, stress-hormone regulation and autonomic nervous-system function. Together, these changes could contribute to the persistent fatigue, cognitive difficulties, sleep problems and other symptoms commonly reported after COVID-19.
The study’s population-based design and detailed information on occupational schedules and sleep habits strengthen the results, but the authors caution that several limitations remain. The participants were all middle-aged adults, so the findings may not apply equally to younger or older populations. Work-related stress, physical demands, exposure to other environmental factors and differences in healthcare access could also contribute to the observed associations. In addition, observational research cannot fully exclude unmeasured confounding or prove that night work or insomnia directly causes long COVID.
Nevertheless, the findings identify sleep as a potentially modifiable factor in post-viral health. Improving sleep quality, reducing unnecessary circadian disruption and providing better support for night-shift workers could become part of broader strategies to reduce the long-term consequences of viral infections. The researchers emphasise that these measures should complement, rather than replace, established approaches to preventing COVID-19 and managing long COVID. Further studies will be needed to determine whether targeted sleep interventions can reduce the risk of persistent symptoms and to clarify how circadian biology interacts with viral infection, obesity and immune recovery.
Subject of Research: People
Article Title: Night work, sleep disruption and long-COVID risk: a population-based cohort study
News Publication Date: 4-Aug-2026
Web References: https://doi.org/10.5271/sjweh.4318; https://www.isglobal.org/en/-/covicat
References: Papantoniou K, Espinosa A, Karachaliou M, Lassale C, Castaño-Vinyals G, Harding B, De Matteis S, Straif K, Alonso E, Dobaño C, Moncunill G, Blay N, Iraola-Guzmán S, de Cid R, Garcia-Aymerich J, Kogevinas M. “Night work, sleep disruption and long-COVID risk: a population-based cohort study.” Scandinavian Journal of Work, Environment and Health. 2026. DOI: 10.5271/sjweh.4318
Keywords: Long COVID, COVID-19, SARS-CoV-2, night-shift work, insomnia, circadian rhythm, sleep disruption, post-viral illness, occupational health, immune response
