Workability, quality of life and cardiovascular risk markers in aging nightshift workers: a pilot study

Study participants were recruited at the General Vienna Hospital between April 2017 and December 2018 among voluntary participants of health-promoting activities organized by the occupational health service and passed down to hospital employees by the head nurses of 16 clinical departments. Night-workers were defined as employees working a rotating shift system with > 3 night shifts/month and controls were defined as employees on permanent day schedules (day workers). The study was approved by the ethics committee of the Medical University of Vienna and conducted in accordance with the Helsinki Declaration and the principles of good clinical practice (EK Number 1260/2017). Informed consent was obtained from all participants before participation in the study. Participants were eligible if they were full-time workers (> 35 h/week) in the hospital (nurses, nurse assistants, patient transporters, administrative staff) and were 45 years of age or older. Participants were excluded if they had a history of cancer, severe cardiometabolic conditions (e.g., myocardial infarction, angina pectoris, type II diabetes, transient ischemia, stroke), and severe psychological conditions (e.g., major depression).

This is a pilot cross-sectional study consisting of questionnaires, anthropometric evaluations, and blood sampling. Participants received a screening questionnaire to determine the final eligibility after consenting to study participation. While the study participants filled out the paper-based questionnaires at their own discretion, blood sampling and anthropometric measurements were conducted primarily on-site by one of the study investigators or the nursing staff themselves. A trained neurologist carried out carotid ultrasound.

Members of the two groups (night workers versus day workers) were descriptively compared with respect to the main outcomes (WAI, QoL, CVD risk markers) and other sociodemographic, lifestyle, sleep, and work-related characteristics. The arithmetic mean and standard deviation were calculated for scale variables and the absolute and relative frequency (presented as percentage) for categorical variables. In univariate analysis, either the t-test, Wilcoxon-Mann-Whitney test, χ²-test, or Fisher’s exact test were used, depending on the type, distribution, and the number of participants per category of the variable. In a subgroup of participants (N = 38) with complete biomarker and confounder information, we used quintile regression analyses to estimate crude, age-adjusted, and multivariate-adjusted (age, smoking status, BMI, physical activity) differences in biomarker levels and 95% CI between rotating night shift workers and day workers. We report quantile regression at the 50th percentile that produces the difference in the median value of the outcome between night shift workers and day workers. We could not run models for selenium due to the small sample size. Analyses were carried out in SPSS v26.0 (IBM Corp. Released 2019. IBM SPSS Statistics for Windows, Version 26.0. Armonk, NY: IBM Corp) and Stata 14.0 (StataCorp. 2015. Stata Statistical Software: Release 14. College Station, TX: StataCorp LP).

While more day workers than night shift workers rated their workability as excellent, WAI scores showed no statistically significant differences between groups. Literature on the association of night shift work with WAI scores is inconclusive. Data from a large Croatian study in hospital employees (N = 1856), conducted by Mustajbegovic et al., indicated that despite excellent overall reports of workability, lower WAI scores correlated with shift work, age, and female sex [30]. In an Iranian study including health professionals and administrative employees, WAI scores were associated with BMI, sleep quality, work schedule, work-related stress, and work-life balance [31, 32]. Data from the European Nurses’ Early Exit Study (N = 7516) showed that sleep quality and psychosocial factors positively impacted workability levels, regardless of work schedule. While sleep quality and quantity did not seem to mediate the effects of work schedule on workability, the authors reported that sleep and working time satisfaction gradually declined with an increase in proportions of night compared to day work. On the other hand, work involvement, motivation, and financial satisfaction were highest in permanent night workers [33]. Perhaps due to similar factors, working night shifts was associated with higher workability scores in a Portuguese cohort [8]. Besides a link between low workability scores and stressful working conditions, lower WAI scores were associated with increased BMI, sleep problems, and fatigue in nurses (age 35 ± 10 years) at a Brazilian public hospital study [34]. A Croatian study reported lower WAI scores, in correlation with professional demands and outcomes of the physical WHOQOL-Bref domain (odds ratio, OR = 0.78; p < 0.001), which encompasses the evaluations of self-reported fatigue, sleep and rest, in shift working emergency medicine staff [9]. In our study participants, a higher prevalence of self-reported sleep problems observed among night workers had no significant impact on total workability scores.

Overall, we found no statistically significant differences in the four QoL domains (physical health, psychological, social relationships, and environment) between rotating night shift and day workers. Most of our participants scored high on all domains of the WHOQOL-Bref, despite many years of rotating night shift work. Workability satisfaction and self-assessed QoL were rated good or excellent by the majority of the study participants. Working night shifts was previously associated with negative outcomes in the psychological and environmental domains of the WHOQOL-Bref in white-collar jobs [35]. Fatigue, which can result from disrupted sleep in night shift workers, appears to be a crucial disruptor of QoL, affecting lifestyle and physical activity [8]. Shift work disorder, i.e., reported insomnia or excessive sleepiness (> 1 month) subjectively relevant to shift work schedules, was not only commonly reported (24.4%) but also related to QoL and severe depressive symptoms in Japanese nurses (N = 1202). The authors showed that night working hours, nap frequency during night shifts, and chronotype were associated with excessive sleepiness, negatively impacting health-related QoL [36]. Although in our study, sleep disorders were more frequently reported by rotating night shift workers compared to day workers, we found no significant reduction in their QoL; however, it should be noted that in our study sample, day workers were also affected by sleep problems, possibly due to their past exposure to night work, which may lead to long-lasting sleep complaints that persist after workers quit night shift work, as suggested by a recent survey among Austrian hospital employees and the general population [37]. This study also showed that different shift schedules might affect, to a different extend, the risk of sleep problems and subsequent impaired daytime functioning. Interestingly, out of several work time organization schedules, French critical care nursing and paramedical employees working 10‑h night shifts had the lowest QoL scores. The authors found that while specific work time scheduling could influence the physical QoL domain, neither fatigue outcomes nor the mental QoL domain were significantly affected [38]. In our study, rotating night workers worked on average 6 night shifts/month, which is a non-intense rotating night shift schedule that might be tolerated well by aging workers and may not lead to higher levels of fatigue and significant changes in QoL. On the other hand, permanent day workers often work on regular early morning schedules, which may result in sleep problems and fatigue among workers with a late chronotype.

This pilot study found no differences in ultrasound CIMT measurements between night and day workers. Most CVD biomarkers did not differ between the two groups, except for lower zinc and higher IL‑6 and CRP levels among night workers. Night shift work is associated with increased CVD risk [12, 18, 19] and several risk factors potentially contributing to CVD and increased risk for CVD [14]. Measurement of subclinical markers of CVD risk such as CIMT have only sporadically been considered in relation to night shift work, and results are ambiguous. One study among subjects > 45 years found an association between shift work and atherosclerosis, showing an increased CIMT [39]. A more recent study showed that night shift work significantly decreased vascular functions, such as arterial stiffness, especially after long-term shift work but did not affect intima media thickness [40]. Our study results indicated slightly higher inflammatory markers in night shift workers (IL‑6, CRP) than day workers but results were not statistically significant. Our findings are in line with most of the current knowledge on the inflammatory effects of shift work originating in experimental studies showing that sleep deprivation may contribute to higher levels of inflammatory markers, such as IL‑6, CRP, and TNF-alpha [41]. Only a few observational studies have tested this hypothesis among shift workers in real-life settings. An increase in inflammatory markers, such as IL‑6 and CRP [14, 15], and leukocyte counts [16, 17] have been associated with working night shifts. In a prospective study among 8000 British doctors, both night shift work and early morning work were associated with risk factors (CRP, BMI, total cholesterol, triglycerides, HbA1c) for CVD [42]. Shift workers had a higher BMI, CRP, total cholesterol, triglycerides, and LDL cholesterol, compared to day work controls in one field study among cocoa-processing workers [14]. Particularly permanent night shift work has been associated with significant dyslipidemia compared to rotating shift work [43]; however, we observed no differences in LDL, HDL, triglycerides, and no difference in BMI between night and day workers. Zinc levels were significantly higher in the day workers compared to the rotating night shift workers in the entire sample, although in the smaller sample with complete confounder association, this association was not significant. Zinc is protective against acute redox stress in cardiomyocytes and prevents inflammatory processes triggered during myocardial damage [28], thus conveying protective effects in CVD and cardiomyopathy. Little is known about the effects of night shift work on zinc levels; however, zinc supplementation was previously associated with improved sleep quality in ICU nurses [44]. The association between night shift work and zinc levels is interesting and needs to be confirmed in larger studies and in confounder-adjusted analyses. No other CVD biomarker differed significantly between the groups. Several reasons could explain this. First, since this was a pilot study, the sample size was not large enough to detect significant differences, if any existed. Second, our study sample appears to have consisted of predominantly healthy participants for their age. This was also indicated by the very low percentage of reported chronic diseases in both groups. Thus, healthy worker effect and in particular healthy night shift worker effect, participants who tolerate night shift work better are selected into night shift work and remain for longer periods, might explain the lack of associations between night shift work and CVD risk markers. Alternatively, a non-intense rotating night shift work schedule (average of 5 nights/month) might not be as detrimental to cardiovascular health as more intense rotating night shift work schedules and permanent night shifts. While the association between night shift work and low to moderated cardiovascular risk seems established in epidemiological studies, the exact mechanisms and the impact of different shift work schedules on CVD risk factors remain unknown. In the larger project, we aim to evaluate if rotating night shift work of low intensity impacts CVD risk factors in hospital workers.

In terms of prevention, atypical working hours (e.g., shift, night, or weekend work) appear not necessarily negatively related to workers’ well-being, especially with high job control and when working time arrangements are in favor of work–life balance [45]; however, individual assessment of night shift work sensitivity and changes in sensitivity with age and health status, as well as stress management training might be a helpful approach [46], with adaptation of work schedules, particularly in sensitive individuals. Fatigue among shift workers with sleep problems might be reduced by decreasing the proportion of night shifts and giving preference to quickly forward-rotating shift systems [47]. Additionally, recommendations on health-promoting measures aimed at obesity, caffeine consumption, smoking, and sleep disorders appear relevant in the aging workers of our study. Regular health examinations encompassing cardiovascular risk factors should be targeted mainly at night shift workers, who in our study were mostly nursing staff and, thus, have a generally better understanding of health and disease but may pay too little attention to their own health—a generation trait in older Austrians and health workers in general.

With emerging evidence on the role of night shift work in QoL, workability and higher risk for CVDs, this pilot study was conducted to examine the feasibility of conducting a larger molecular epidemiological study on this topic. This pilot supports the feasibility and initial acceptability of the proposed procedures among aging hospital employees in the suggested hospital setting. Participants overall responded positively to the study invitation, 70 were recruited, filled out questionnaires, and came in for body analysis, carotid ultrasound, and biological sampling collection. Most procedures (questionnaires, body composition analysis, biological sample collection, and biomarker analysis) are feasible and gave high-quality data. Biomarker and CIMT analyses were less well powered due to study participants not attending blood sampling or ultrasound. Our results require validation in a larger population. The study team is considering offering incentives and shortening the questionnaire length in order to increase participation rates and improve the chances of participants completing all study procedures in the larger study.

While the extent of our conducted health examinations is a strength of this study, there are some limitations regarding our results. Firstly, due to the feasibility character of our study, sample size did not allow multivariate statistical analysis and the power was limited to detect significant differences between the groups if they exist. Secondly, since participation in the study was voluntary and conducted without a specific incentive for study adherence, several measurements were affected by missing data, thus limiting our analytical sample. Lastly, and due to the same reason, a selection bias leading to a selection in our study of particularly healthy workers cannot be excluded. In our pilot project, we did not have enough power to evaluate individual risk differences in subgroups. Still, in the larger study, we plan to evaluate susceptibility to night shift work in relation to chronic disease risk in relevant subgroups taking into account shift work adaptation, shift work tolerance and chronotype.

In our study of aging hospital employees, we found no significant differences in workability and quality of life (QoL) between night and day workers. Our study is to our knowledge the first to describe lower zinc levels, a micronutrient with anti-inflammatory properties previously associated with cardiovascular disease (CVD) and sleep quality, in night shift workers; however, in a reduced sample of our data, this association was not significant after adjusting for potential confounders. The reported higher levels of inflammation markers (C-reactive protein [CRP], interleukin-6 [IL-6]) are in line with previous studies showing a potentially elevated CVD risk in night shift workers, which should be considered in occupational health and disease prevention.