Shiftwork
Monday 6 October 2025, 14.00 – 15.30 Flash
Chairs: Kirsten Nabe-Nielsen, Antonio D’Errico
A newly developed circadian imbalance index (CII) and risk of cardiovascular-kidney-metabolic disease in the UK biobank
Jing Zhang (presenter)
Dat Thien Tran, Tala El Ghoul, Susanne Strohmaier, Magdalena Żebrowska, Susan Redline, Martin K Rutter, Eva Schernhammer
Abstract
Objectives: To prospectively evaluate the association between combined circadian imbalance related traits and cardiovascular-kidney-metabolic (CKM) disease incidence, and their interaction with night shift work.
Methods: 191,764 UK Biobank participants employed and without major chronic diseases at baseline were included. Our novel score incorporates factors that may adversely affect the circadian system – the Circadian Imbalance Index (CII), with evening chronotype, short or long sleep duration (≥9 or ≤6 hours/day), high neuroticism score (≥7), atypical caffeine consumption (0 or ≥5 caffeinated coffee cups/day), and low vitamin D levels (<50 nmol/L), each contributing 1 point if present, resulting in a scale ranging from 0-5. Current night shift work status was categorized as day workers, shift workers and night shift workers. The CKM outcome comprised type 2 diabetes, cardiovascular diseases and chronic kidney diseases, identified via inpatient ICD codes, self-reports, or death records. Cox models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs), investigating associations between the CII and CKM incidence, and effect modification by night shift work.
Results: During a median follow-up of 13.5 years, 16,907 incident CKM cases were identified. A significant trend of CKM risk with increasing CII was observed in participants of European (Ptrend<0.001) and Asian (Ptrend<0.001), but not in African ancestry. Among Europeans, the adjusted HR for CKM comparing participants scoring highest to those scoring 0-1 on CII was 1.95 (95%CI: 1.70-2.23; Ptrend<0.001). The joint effect of high CII and night shift work on CKM was HR=2.22 (95%CI: 1.95-2.53), with a significant additive interaction (P<0.05).
Conclusion: We observed an association between CII and CKM incidence in Europeans and Asians. Among Europeans, a high CII combined with night shift work was associated with the highest CKM rate, suggesting that maintaining low CII may help prevent CKM disease, with greater benefits observed for night shift workers.
Circadian disruption of steroid hormone rhythms in night shift workers: Findings from the EPHOR-NIGHT study
Gemma Castaño-Vinyals (presenter)
Ana Espinosa, Oscar Pozo, Maria Albin, Karin Broberg, Anne Helene Garde, Kirsten Nabe-Nielsen, Manolis Kogevinas, Barbara Harding
Abstract
Objective: Night shift work affects circadian rhythms, yet its influence on the rhythmicity of steroid hormones remains insufficiently characterized in large epidemiological studies. We examined the association between night shift work and the diurnal patterns of melatonin and steroid hormone metabolites using cosinor analysis in the EPHOR-NIGHT multicenter European cohort.
Material and Methods: We included 590 workers (336 night shift and 254 day workers) from Spain, Sweden and Denmark. Participants reporting use of melatonin supplements were excluded. Participants provided repeated saliva samples (n=5) over the course of one day, enabling the characterization of circadian rhythms for melatonin and steroid hormone metabolites. Cosinor models were fitted to estimate individual mesor (rhythm-adjusted mean) and acrophase (timing of peak), and associations with night shift work compared to permanent day work were evaluated using geometric mean ratios (GMRs) and differences (GMDs), adjusting for age, sex, educational level, season, and study center.
Results: Night shift work was associated with marked delays in acrophase for all hormones studied. Melatonin showed a 2.5-hour delayed peak (GMD: 2.46 hours; 95% CI: 1.36–3.56), while cortisol and several of its metabolites—including 20α- and 20β-dihydrocortisol, and 5α-tetrahydrocortisol—exhibited peak delays of approximately 3.2 to 3.9 hours (all p<0.001). Additionally, night shift workers demonstrated lower mesor levels for all metabolites examined but only significant for cortisol (GMR: 0.81; 95% CI: 0.70–0.95), 20α-dihydrocortisol (GMR: 0.83; 95% CI: 0.74–0.94), and 5α-tetrahydrocortisol (GMR: 0.84; 95% CI: 0.72–0.97), indicating a reduction in overall hormone production.
Conclusion: We observed that night shift work is associated with both a delayed circadian phase and reduced mean levels of melatonin and cortisol-related metabolites. These results support the hypothesis that circadian misalignment in shift workers leads to systemic hormonal disruption, potentially contributing to long-term health risks associated with shift work.
Funding: Horizon2020 (874703) and FIS (PI22/01683).
Does the duration of exposure to night work modify the 10-year risk of cardiovascular disease? Results from Constances, a French population-based cohort
Stephanie Boini (presenter)
Ève Bourgkard, Mathieu Dziurla, Michel Grzebyk, Céline Ribet, Jean Ferrières, Yolande Esquirol
Abstract
Objective: To evaluate the effect of the duration of exposure to night work on the 10-year risk of cardiovascular disease (SCORE2).
Material and methods: Based on the Constances cohort, 52,234 participants divided into day and night workers (permanent, rotating and former night workers) were included. The duration of exposure to night work was assessed over the entire working career using a self-reported questionnaire. The 10 year-cardiovascular disease risk was assessed using the SCORE2, following recently established guidelines and based on the main cardiovascular factors measured. Generalized additive models were used to estimate the probability of having a moderate or high SCORE2 (OR and 95% confidence intervals) as a function of the duration of exposure for each category of night workers.
Results: The sample consisted of 24,892 men and 27,342 women, with an average working career of 20 years. Among them, 685 permanent night workers, 915 rotating night workers and 2,972 former night workers were identified. Compared to daytime workers, the ORs for a moderate or high SCORE2 were 1.43 [1.23-1.66] for permanent, 1.72 [1.51-1.97] for rotating and 2.01 [1.87-2.18] for former night workers. As the cumulative duration of exposure increased, the probability of having a moderate and high SCORE2 increased. Indeed, significant excess risk was observed from 10 years of cumulative exposure in permanent night workers (OR=1.28) and rotating night workers (OR=1.48). In former night workers, this significant excess risk was observed from 5 years of cumulative exposure (OR=1.82).
Conclusion: These results from a French cohort confirm a high 10-year risk of developing cardiovascular disease in night workers, with a significant effect from 10 years of exposure. The risk remains among former night workers despite the cessation of exposure. These results reinforce the need to monitor cardiovascular risk in this type of worker, even after stopping night work.
Effect of shift work on blood pressure and markers of obesity in the EPHOR-NIGHT WORK study
Jesse Thacher (presenter)
Barbara N. Harding, Caisa Laurell, Maria Albin, Anastasia Snigireva, Frida Wiik, Gunilla Rydenstrand, Jelle Vlaanderen, Anne Helene Garde, Manolis Kogevinas, Karin Broberg
Abstract
Objective: Shift work, particularly night shifts, have been linked to poor cardiometabolic outcomes. However, the mechanistic pathways underlying these associations are not completely understood. We aimed to evaluate the effect of night shift work on blood pressure and markers of obesity in workers from Spain, Sweden, and Denmark.
Material and Methods: A total of 860 participants aged 21-67 years (mean age 42.6) were included from the EPHOR-NIGHT study, comprising 363 day shift workers and 497 nightshift workers, primarily employed in the healthcare sector. Participants completed a baseline questionnaire and systolic (SBP), diastolic blood pressure (DBP), along with anthropometric parameters were measured by trained personnel. Linear and logistic regression models, adjusting for sociodemographic and lifestyle factors, were used to assess associations between night shift work and blood pressure, hypertension (≥140/90 mmHg), as well as body mass index (BMI), waist circumference, waist–hip ratio, overweight, and abdominal obesity using WHO definitions.
Results: Compared to day workers, night shift work was associated with a 2.85-mmHg increase (95% confidence interval (CI): 0.50-5.19) in SBP and possibly with DBP (β=1.12; 95% CI: -0.53-2.77 mmHg). We observed a higher odds ratio for hypertension (OR=1.59; 95% CI: 1.06-2.38). We also observed a dose-response pattern of hypertension risk per night shifts worked on consecutive days (p for trend 0.03). Night shift work was also associated with higher BMI (β=0.88; 95% CI: 0.09-1.68), and potentially with overweight (OR=1.14; 95% CI: 0.81-1.62) or abdominal obesity (OR=1.30; 95% CI: 0.87-1.94).
Conclusion: We found that compared with day workers, night shift work was associated with elevated blood pressure and BMI, two important cardiometabolic risk factors.
Night and shift work and medically certified sickness absence due to common mental disorders among healthcare staff: A prospective cohort study
Tove Nilsson (presenter)
Emma Brulin, Mikko Härmä, Per Gustavsson, Carolina Bigert, Abid Lashari, Jenny Selander, Seth Addo
Abstract
Objective: The aim is to investigate the risk of first-time medically certified sickness absence (>14 days) due to common mental disorders (CMDs) in healthcare staff by types of shift work (shift work with evenings and/or night shifts, consecutive nights and quick returns).
Methods: The design was a prospective cohort study with an 11-year follow-up. 25,631 nurses and nurse assistants with more than 100 shifts per year employed for at least one year between 2008-2019 by Region Stockholm were included. Detailed information on working hours was obtained from a computerized employee register. Data on first-time medically certified sickness absence due to CMDs (N=5,122) was obtained from the Swedish Social Insurance Agency. Cox regression analyses were used to estimate hazard ratios (HR), adjusting for age, profession, sex, and country of birth.
Results: A decreased risk of sickness absence due to CMDs was found among those who, during the preceding year, had night shift work (HR 0.80, 95% CI 0.72-0.89), and worked only nights (HR 0.81, 95% CI 0.65-0.99), compared to day workers. Frequently working nights (>121 shifts in 1 year) showed a decreased risk of sickness absence (HR 0.77, 95% CI 0.65-0.90) compared to those who never work nights. Frequently (>49 times in 1 year) having quick returns from afternoon shifts (<11 h) showed a decreased risk of sickness absence (HR 0.87, 95% CI 0.75-1.00) compared to day workers.
Conclusion: Intensive night work was associated with a decreased risk of sickness absence due to CMDs in healthcare staff. The reason for this finding is not known but could be related to a selection of psychically fit individuals for night-work, partly related to mandatory medical examinations of night workers.
Fundings: The study was funded by FORTE: Swedish Research Council for Health, Working Life and Welfare (Grant no. 2017-01947; 2021-00386).
Night shift work may impair glucose levels at night: A field study among female hospital employees
Rasmus Reeh (presenter)
Anders Aagaard, Nanna Lind, Jannet Svensson, Thomas Mandrup-Poulsen, Kirsten Nabe-Nielsen, Anne Helene Garde
Abstract
Objective: Alternating around-the-clock work schedules disrupt the natural circadian rhythms, resulting in circadian misalignment that increases risks for metabolic and cardiovascular diseases. How night shift work affects glycemic profiles in real-world settings remains to be settled. We hypothesized that working during the night impairs glucose levels among female hospital employees compared to shift work during the day.
Material and Methods: The study employs an observational design in which a subgroup of the 1001 nights-cohort in Denmark of 57 female hospital employees without known diabetes were found eligible to register working hours, sleep, and food intake in diaries while wearing a Continuous Glucose Monitor (CGM, Dexcom) for seven days. A night shift was defined as working 8 hours from 23:00 to 07:00, and a day shift as working 8 hours from 07:00 to 15:00. A “night off” and a “day off” were defined as not working during these intervals. The study included 39 participants, each having (1) at least one night shift and off night and/or (2) at least one day shift and off day. Thirty-five participants had both. Daily mean and standard error of glucose levels at night and day shifts and at off nights and days were calculated.
Results: Participants completed a total of 76 night shifts and 276 nights off, along with 72 day shifts and 246 days off. The mean glucose levels were 116.0 (SEM 1.9) mg/dL during night shifts, 113.2 (SEM 0.9) mg/dL during nights off, 111.7 (SEM 1.6) mg/dL during day shifts, and 111.7 (SEM 1.0) mg/dL during days off.
Conclusion: Shift work may modestly increase mean glucose levels at night but not at daytime. Results of other CGM-derived outcome variables and ongoing statistical variance component modeling using the within-person design will be presented at the conference.
The Danish Working Environment Research Fund (26202009; 19202209), The Health Foundation (22B0452), the European Union’s Horizon (# 874703), NFA, and The Danish Cardiovascular Academy