Schichtarbeit und Krebserkrankungen

Die gesundheitlichen Auswirkungen von Schicht- und Nachtarbeit sind Gegenstand vieler wissenschaftlicher Untersuchungen. Das Spektrum möglicher Erkrankungen und Endpunkte, die mit Schicht- und Nachtarbeit assoziiert sind, reicht von chronischen Erkrankungen wie Krebs, Herz-Kreislauf-Erkrankungen über Schlafstörungen, psychische Belastungen bis hin zu Reproduktionsstörungen und Unfällen. Im Juni 2019 stufte die Internationale Krebsagentur (IARC) Nachtarbeit als wahrscheinlich krebserregend ein (Gruppe 2A) und bestätigte damit ihre Einschätzung aus dem Jahr 2007. Die Expertengruppe der IARC weist dabei auf die immer noch sehr heterogenen Studienergebnisse hin. Während der überwiegende Teil der populationsbasierten Fall-Kontroll-Studien positive Assoziationen zwischen Schichtarbeit und Krebserkrankungen zeigte, wurde in vielen Kohorten-Studien keine Assoziation beobachtet. Die Frage, ob erhöhte Krebsrisiken tatsächlich auf Schicht- oder Nachtarbeit zurückgeführt werden können, kann daher zurzeit nicht zweifelsfrei beantwortet werden. Der folgende Beitrag gibt einen Überblick zu offenen Fragen und Aspekten der Schichtarbeitsforschung am Beispiel von Krebserkrankungen und diskutiert die aktuelle arbeitsmedizinische Einschätzung.The health effects of shift and night work have been the subject of many scientific studies. The spectrum of possible diseases and endpoints associated with shift and night work range from chronic diseases, such as cancer and cardiovascular diseases, over sleep disorders and psychological stress up to reproductive disorders and accidents. In June 2019 the International Agency for Research on Cancer (IARC) classified night work as probably carcinogenic to humans (group 2A), thus confirming its previous assessment from 2007. The IARC expert group pointed out the continuing large heterogeneity of the study results. The majority of population-based case-control studies showed positive associations between shift work and cancer, whereas in many cohort studies no such associations were observed. Therefore, the question as to whether increased cancer risks can actually be attributed to shift or night work cannot yet be answered with certainty. This article provides an overview of open questions and aspects of shift work research using the example of cancer and discusses the current implications for occupational health

Decreased psychomotor vigilance of female shift workers after working night shifts

$\bf Background$ We compared psychomotor vigilance in female shift workers of the Bergmannsheil University Hospital in Bochum, Germany (N = 74, 94% nurses) after day and night shifts. $\bf Methods$ Participants performed a 3-minute Psychomotor Vigilance Task (PVT) test bout at the end of two consecutive day and three consecutive night shifts, respectively. Psychomotor vigilance was analyzed with respect to mean reaction time, percentage of lapses and false starts, and throughput as an overall performance score, combining reaction time and error frequencies. We also determined the reaction time coefficient of variation (RTCV) to assess relative reaction time variability after day and night shifts. Further, we examined the influence of shift type (night vs. day) by mixed linear models with associated 95% confidence intervals (CI), adjusted for age, chronotype, study day, season, and the presence of obstructive sleep apnea (OSA). $\bf Results$ At the end of a night shift, reaction times were increased ($\beta$ = 7.64; 95% CI 0.94; 14.35) and the number of lapses higher compared to day shifts (exp(($\beta$) = 1.55; 95% CI 1.16–2.08). By contrast, we did not observe differences in the number of false starts between day and night shifts. Throughput was reduced after night shifts (($\beta$ = -15.52; 95% CI -27.49; -3.46). Reaction times improved across consecutive day and night shifts, whereas the frequency of lapses decreased after the third night. RTCV remained unaffected by both, night shifts and consecutive shift blocks. $\bf Discussion$ Our results add to the growing body of literature demonstrating that night-shift work is associated with decreased psychomotor vigilance. As the analysis of RTCV suggests, performance deficits may selectively be driven by few slow reactions at the lower end of the reaction time distribution function. Comparing intra-individual PVT-performances over three consecutive night and two consecutive day shifts, we observed performance improvements after the third night shift. Although a training effect cannot be ruled out, this finding may suggest better adaptation to the night schedule if avoiding fast-changing shift schedules

Night work, chronotype and cortisol at awakening in female hospital employees

To examine the effect of night shift on salivary cortisol at awakening (C1), 30 min later (C2), and on the cortisol awakening response (CAR, the difference between C2 and C1). We compared shift and non-shift workers with a focus on the impact of worker chronotype. Our study included 66 shift-working females (mean age = 37.3 years, SD = 10.2) and 21 non-shift working females (mean age = 47.0 years, SD = 8.9). The shift workers collected their saliva samples at C1 and C2 on each two consecutive day shifts and night shifts. Non-shift workers collected their samples on two consecutive day shifts. We applied linear mixed-effects models (LMM) to determine the effect of night shift on CAR and log-transformed C1 and C2 levels. LMMs were stratified by chronotype group. Compared to non-shift workers, shift workers before day shifts (i.e. after night sleep) showed lower cortisol at C1 (exp ($\hat \beta$)=0.58, 95% CI 0.42, 0.81) but not at C2. In shift workers, the CARs after night shifts (i.e. after day sleep) were lower compared to CARs before day shifts ($\hat \beta$= − 11.07, 95% CI − 15.64, − 6.50). This effect was most pronounced in early chronotypes (early: $\hat \beta$= − 16.61, 95% CI − 27.87, − 5.35; intermediate: $\hat \beta$= − 11.82, 95% CI − 18.35, − 5.29; late: $\hat \beta$= − 6.27, 95% CI − 14.28, 1.74). Chronotype did not modify the association between night shift and CAR. In our population of shift workers, there was a mismatch between time of waking up and their natural cortisol peak at waking up (CAR) both during day and night shift duties

Naphthalene

$\bf Objective$ This cross-sectional study determined whether acute sensory irritative or (sub)chronic inflammatory effects of the eyes, nose or respiratory tract are observed in employees who are exposed to naphthalene at the workplace. $\bf Methods$ Thirtynine healthy and non-smoking male employees with either moderate ($\it n$ = 22) or high ($\it n$ = 17) exposure to naphthalene were compared to 22 male employees from the same plants with no or only rare exposure to naphthalene. (Sub)clinical endpoint measures included nasal endoscopy, smell sensitivity, self-reported work-related complaints and the intensity of naphthalene odor and irritation. In addition, cellular and soluble mediators in blood, nasal lavage fluid (NALF) and induced sputum (IS) were analysed. All measurements were carried out pre-shift on Monday and post-shift on Thursday. Personal air monitoring revealed naphthalene shift concentrations up to 11.6 $mg/m^{3}$ with short-term peak concentrations up to 145.8 $mg/m^{3}$ and 1- and 2-naphthol levels (sum) in post-shift urine up to 10.1 mg/L. $\bf Results$ Acute sensory irritating effects at the eyes and upper airways were reported to occur when directly handling naphthalene (e.g., sieving pure naphthalene). Generally, naphthalene odor was described as intense and unpleasant. Habituation effects or olfactory fatigue were not observed. Endoscopic examination revealed mild inflammatory effects at the nasal mucosa of exposed employees in terms of reddening and swelling and abnormal mucus production. No consistent pattern of cellular and soluble mediators in blood, NALF or IS was observed which would indicate a chronic or acute inflammatory effect of naphthalene in exposed workers. $\bf Conclusions$ The results suggest that exposure to naphthalene induces acute sensory irritative effects in exposed workers. No (sub)chronic inflammatory effects on the nasal epithelium or the respiratory tract could be observed under the study conditions described here