Shiftwork Duration and the Awakening Cortisol Response Among Police Officers

Police officers are required to work irregular hours, which induces stress, fatigue, and sleep disruption, and they have higher rates of chronic disease and mortality. Cortisol is a well-known “stress hormone” produced via activation of the hypothalamic-pituitary-adrenal axis. An abnormal secretion pattern has been associated with immune system dysregulation and may serve as an early indicator of disease risk. This study examined the effects of long- and short-term shiftwork on the cortisol awakening response among officers (n = 68) in the Buffalo Cardio-Metabolic Occupational Police Stress (BCOPS) pilot study (2001–2003). The time each officer spent on day (start time: 04:00–11:59?h), afternoon (12:00–19:59?h), or night (20:00–03:59?h) shifts was summarized from 1994 to examination date to characterize long-term (mean: 14 ± 9 yrs) and short-term (3, 5, 7, or 14 days prior to participation) shiftwork exposures. The cortisol awakening response was characterized by summarizing the area under the curve (AUC) for samples collected on first awakening, and at 15-, 30-, and 45-min intervals after waking. Data were collected on a scheduled training or off day. The cortisol AUC with respect to ground (AUC_G) summarized total cortisol output after waking, and the cortisol AUC with respect to increase (AUC_I) characterized the waking cortisol response. Officers also completed the Center for Epidemiologic Studies Depression scale. Waking cortisol AUC values were lower among officers working short-term night or afternoon shifts than day shifts, with maximal differences occurring after 5 days of shiftwork. The duration of long-term shiftwork was not associated with the cortisol awakening response, although values were attenuated among officers with more career shift changes. (Author correspondence: burch@mailbox.sc.edu)     

Adipokine Levels Are Altered by Shiftwork: A Preliminary Study

Shiftwork is often associated with metabolic diseases, and in the past few years, several cytokines have been postulated to contribute to various diseases, including insulin resistance. The aim of this study was to compare the concentrations of adiponectin, tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) in samples of young adult men exposed to a fixed (i) night shift (n?=?9), working from 22:00 to 06:00?h; (ii) early morning shift (n?=?6), working from 06:00 to 14:00?h; and (iii) day shift (n?=?7), working from 08:00 to 17:00?h. The fixed night-shift and early-morning-shift samples were considered collectively as a shiftworker group given their work times. Blood samples were collected during the regular working day at 4-h intervals over the course of 24?h, thus totaling six samples. Morphological and physical activity parameters did not differ between the three groups. Total energy intake was lowest on the early morning shifts (p?<?.03). Both shiftworker groups ingested a significantly higher percentage of fat (p?<?.003) and a lower percentage of carbohydrate (p?<?.0005) than the day group. The early morning group had a lower mean 24-h level of adiponectin than the other two groups (p?=?.016), and both the early morning and night groups exhibited higher mean 24-h levels of TNF-α than the day group (p?=?.0001). The 24-h mean levels of IL-6 did not differ significantly between the groups (p?=?.147). None of the groups exhibited a significant circadian effect on adiponectin (p?=?.829), TNF-α (p?=?.779), or IL-6 (p?=?.979) levels. These results indicate that individuals who are enrolled in shiftwork are susceptible to alterations in the secretion of cytokines that are involved in insulin resistance and cardiovascular disease, both of which are known to affect this population. (Author correspondence: tmello@demello.net.br)     

对215例代谢综合症患者进行健康教育指导及其效果观察

目的：通过对代谢综合征（Ms）患者进行积极健康教育指导,探索促进代谢综合征患者的健康对策,减轻代谢综合征对人体的危害,提高生活质量。方法：对我科住院健康体检中确诊的215例代谢综合征患者进行健康教育指导,其中包括饮食、运动、药物应用指导、定时检测、生活方式和行为等护理干预,一年后统计分析干预前后患者危险因素,血糖、血脂、体重指数、血压等指标的变化。结果：干预后患者危险因素显著减少,空腹血糖、血甘油三脂、总胆固醇、体重指数、收缩压与舒张压等指标与干预前比较差异有统计学意义（P〈0．01）。结论：表明健康教育对延缓MS的进展及减少并发症的发生是一种有效的干预手段。     

Unaltered Instrumental Learning and Attenuated Body-Weight Gain in Rats During Non-rotating Simulated Shiftwork

Exposure to shiftwork has been associated with multiple health disorders and cognitive impairments in humans. We tested if we could replicate metabolic and cognitive consequences of shiftwork, as reported in humans, in a rat model comparable to 5 wks of non-rotating night shifts. The following hypotheses were addressed: (i) shiftwork enhances body-weight gain, which would indicate metabolic effects; and (ii) shiftwork negatively affects learning of a simple goal-directed behavior, i.e., the association of lever pressing with food reward (instrumental learning), which would indicate cognitive effects. We used a novel method of forced locomotion to model work during the animals' normal resting period. We first show that Wistar rats, indeed, are active throughout a shiftwork protocol. In contrast with previous findings, the shiftwork protocol attenuated the normal weight gain to 76?±?8?g in 5 wks as compared to 123?±?15?g in the control group. The discrepancy with previous work may be explained by the concurrent observation that with our shiftwork protocol rats did not adjust their between-work circadian activity pattern. They maintained a normal level of activity during the “off-work” periods. In the control experiment, rats were kept active during the dark period, normally dominated by activity. This demonstrated that forced activity, per se, did not affect body-weight gain (mean±SEM: 85?±?11?g over 5 wks as compared to 84?±?11?g in the control group). Rats were trained on an instrumental learning paradigm during the fifth week of the protocol. All groups showed equivalent increases in lever pressing from the first (3.8?±?.7) to the sixth (21.3?±?2.4) session, and needed a similar amount of sessions (5.1?±?.3) to reach a learning criterion (≥27 out of 30 lever presses). These results suggest that while on prolonged non-rotating shiftwork, not fully reversing the circadian rhythm might actually be beneficial to prevent body-weight gain and cognitive impairments. (Author correspondence: C.Leenaars@nin.knaw.nl)     

20th International Symposium on Shiftwork and Working Time: Biological Mechanisms,Recovery, and Risk Management in the 24-h Society

This dedicated issue of Chronobiology International is devoted to the selected proceedings of the 20th International Symposium on Shift Work and Working Time held in Stockholm, Sweden, 28 June to 1 July 2011. It constitutes the fifth such issue of the journal since 2004 dedicated to the selected proceedings to the meetings of the Working Time Society. The key theme of the 20th Symposium was “Biological Mechanisms, Recovery, and Risk Management in the 24-h Society.” The collection of papers of this dedicated issue represents the best of contemporary research on the effects of night and rotating shift schedules on worker health and safety. The contents cover such topics as sleep restriction, injuries, health, and performance of night work and rotating shiftwork, plus light treatment as a countermeasure against the circadian disruption of shiftwork. The majority of the papers are observational field studies, including some of large sample size, and three studies are well-designed laboratory experiments. (Author correspondence: goran.kecklund@stress.su.se)     

Focus Group Evaluation of Night Nurse Shiftwork Difficulties and Coping Strategies

Focus group interviews were performed on 45 intensive care nurses who worked 12-h shifts in a large metropolitan hospital. The purpose of this study was to identify nurses' perceptions of difficulties associated with shiftwork and coping strategies used to combat them. Overall, the findings were not different than those currently discussed in the literature. For example, nurses frequently utilized white noise, telephone answering machines, and light-darkening shades to improve the quality and quantity of day sleep. They also used exercise and increased early shift caffeine consumption to improve night work performance. However, the major incentive for performing night work for these nurses was a high shift differential that equaled approximately 20% of their hourly salary. Most nurses also felt that group educational interventions regarding shiftwork difficulties and coping strategies would be preferred to individual counseling. The most significant finding of this study was the discovery of an extremely high incidence (95%) of automobile-related injuries and near-accidents that occurred while driving to and from the workplace, potentially posing a significant public health risk. (Chronobiology International, 13(6), 457-463, 1996)     

Focus Group Evaluation of Night Nurse Shiftwork Difficulties and Coping Strategies

Focus group interviews were performed on 45 intensive care nurses who worked 12-h shifts in a large metropolitan hospital. The purpose of this study was to identify nurses' perceptions of difficulties associated with shiftwork and coping strategies used to combat them. Overall, the findings were not different than those currently discussed in the literature. For example, nurses frequently utilized white noise, telephone answering machines, and light-darkening shades to improve the quality and quantity of day sleep. They also used exercise and increased early shift caffeine consumption to improve night work performance. However, the major incentive for performing night work for these nurses was a high shift differential that equaled approximately 20% of their hourly salary. Most nurses also felt that group educational interventions regarding shiftwork difficulties and coping strategies would be preferred to individual counseling. The most significant finding of this study was the discovery of an extremely high incidence (95%) of automobile-related injuries and near-accidents that occurred while driving to and from the workplace, potentially posing a significant public health risk. (Chronobiology International, 13(6), 457–463, 1996)     

Epigenetic Impact of Long-Term Shiftwork: Pilot Evidence From Circadian Genes and Whole-Genome Methylation Analysis

Epigenetic association studies have demonstrated differential promoter methylation in the core circadian genes in breast cancer cases relative to cancer-free controls. The current pilot study aims to investigate whether epigenetic changes affecting breast cancer risk could be caused by circadian disruption through exposure to light at night. Archived DNA samples extracted from whole blood of 117 female subjects from a prospective cohort conducted in Denmark were included in this study. A polymerase chain reaction (PCR)-based method was used for detection of gene-promoter methylation, whereas genome-wide methylation analysis was performed using the Illumina Infinium Methylation Chip. Long-term shiftwork resulted in the same promoter hypomethylation of CLOCK and hypermethylation of CRY2, as was previously observed in breast cancer case-control studies. Genome-wide methylation analysis further discovered widespread methylation alterations in shiftworkers, including changes in many methylation- and cancer-relevant genes. Pathway analysis of the genes with altered methylation patterns revealed several cancer-related pathways. One of the top three networks generated was designated as “DNA replication, recombination, and repair, gene expression, behavior” with ESR1 (estrogen receptor α) featured most prominently in the network, underscoring the potential breast cancer relevance of the genes differentially methylated in long-term shiftworkers. These results, although exploratory, demonstrate the first evidence of the cancer-relevant epigenetic effects of night shiftwork, which warrant further investigation. Considering there are millions of shiftworkers worldwide, understanding the effects of this exposure may lead to novel strategies for cancer prevention and new policies regulating shiftwork. (Author correspondence: yong.zhu@yale.edu)     

姜黄素治疗代谢综合征的研究进展

姜黄素是从姜黄中提取的一种多酚类物质,近年来对姜黄素的研究日趋广泛,已明确具有抗肿瘤,抗炎,抗氧化、降糖、降脂等多种药理作用,在临床上广泛应用于治疗肿瘤、肥胖、糖尿病等多种疾病.代谢综合征是一组以代谢紊乱为特征的症候群,包括中心性肥胖、糖脂代谢异常、高血压、非酒精性脂肪肝等,这些病理状态长期发展,可进一步导致心、脑血管患病率明显升高,研究发现姜黄素能够改善代谢综合征.现就近年来有关姜黄素治疗代谢综合征的研究进展综述如下.     

Effect of Shiftwork on Systemic Markers of Inflammation

Shiftwork is associated with an increased risk of cardiovascular diseases, but the possible role of inflammation in this relationship is not well known. We tested the hypothesis that shiftwork would be associated with higher levels of C-reactive protein (CRP) and increased leukocyte count. We analyzed the cross-sectional associations between work arrangements and low-grade inflammation in 1877 airline-company employees separately for men (n?=?1037) and women (n?=?840). The participants were classified into five categories according to their work schedule: day workers who have not worked in shifts (referent group), former shiftworkers, 2-shift workers, 3-shift workers, and in-flight workers. In models adjusted for age and recent infectious diseases, CRP levels were higher among male 3-shift workers (p = .002) and marginally higher in male 2-shift workers (p = .076). In addition, leukocyte count was higher in 2-shift (p = .005) and 3-shift (p = .021) working men. In women, CRP level was higher in 2-shift workers (p = .028), whereas leukocyte count was lower in flight workers (p = .005). Any separate adjustment additionally for smoking, education, alcohol consumption, physical activity, and obesity did not substantially affect the results of 2- and 3-shift work. In the fully adjusted model, only the association between 3-shift work and CRP in men (p = .021) and 2-shift work and leukocyte count in men (p = .020) and leukocyte count in 3-shift-working women (p = .044) were significant. Our results suggest that 2- and 3-shift work is associated with increased systemic inflammation and the relationship is relatively independent of the considered risk factors of cardiovascular disease. (Author correspondence: Sampsa.Puttonen@ttl.fi)     

Hair Tissue Mineral Analysis and Metabolic Syndrome

Deficiency of minerals causes functional abnormality of enzymes, frequently resulting in metabolic disturbance. We investigated possible relationship between minerals and metabolic syndrome by analysis of hair tissue minerals. We selected 848 subjects older than 20 years of age at Ajou University Hospital from May 2004 to February 2007. We excluded the subjects who had cancers, steroid and thyroid medication, and incomplete record from the study. Finally, 343 subjects were eligible. We performed cross-sectional analysis for the relationship between minerals and metabolic syndrome. The contents of calcium, magnesium, and copper in the metabolic syndrome group were significantly lower than those of the normal group, whereas the amounts of sodium, potassium, and mercury in the metabolic syndrome group were significantly higher than those of the normal group. By dividing the subjects into quartile with the level of calcium, magnesium, and mercury concentrations, we carried out logistic regression analysis to study the subjects and found that the subjects in the third quartile of calcium and magnesium concentrations had significantly lower odds ratio (OR) of the metabolic syndrome compared with that of the lowest quartile group [OR = 0.30, confidence interval (CI) = 0.10–0.89; OR = 0.189, CI = 0.063–0.566] and that the subjects in the highest mercury quartile had significantly higher OR of the metabolic syndrome compared with that of the lowest mercury quartile group (OR = 7.35, CI = 1.73–31.1). As part of the metabolic syndrome, the optimal calcium and magnesium concentrations in hair tissue may reflect decreased risk of metabolic syndrome, whereas high mercury concentration in hair tissue may indicate increased risk of metabolic syndrome.     

Unfolded Protein Response Signaling and Metabolic Diseases

The endoplasmic reticulum (ER) is a central organelle for protein biosynthesis, folding, and traffic. Perturbations in ER homeostasis create a condition termed ER stress and lead to activation of the complex signaling cascade called the unfolded protein response (UPR). Recent studies have documented that the UPR coordinates multiple signaling pathways and controls various physiologies in cells and the whole organism. Furthermore, unresolved ER stress has been implicated in a variety of metabolic disorders, such as obesity and type 2 diabetes. Therefore, intervening in ER stress and modulating signaling components of the UPR would provide promising therapeutics for the treatment of human metabolic diseases.     

Promoting Sleep in Shiftworkers and Inter Continental Travelers

A number of techniques and treatments can be used to alleviate the sleep disturbance associated with both shiftwork and transmeridian travel. Optimization of the sleeping environment and avoidance of substances such as caffeine and alcohol before sleep are the best initial approach. Timing sleep to coincide with some of the normal sleep period where possible will improve sleep quality in shiftworkers. Similarly, following transmeridian flight, restricting sleep to the nocturnal period in the new time zone will assist adaptation. Hypnotic drugs may be of benefit to alleviate sleep disturbance experienced by shiftworkers or transmeridian travelers. Selection of the most appropriate medication must take into account required duration of action and possible residual effects of the drug on alertness. Hypnotics may be useful, particularly in middle-aged individuals who already have disturbed sleep, on those occasions when poor sleep is anticipated, for example following an eastward flight or after the initial change to night duty. Over-the-counter preparations should be avoided whenever possible unless it is known that they are not associated with residual sequelae. (Chronobiology International, 14(2), 133–143, 1997)     

微量白蛋白尿与2型糖尿病合并代谢综合征的相关性

目的:探讨2型糖尿病(T2DM)患者微量白蛋白尿与代谢综合征(MS)的相关性。方法:282例T2DM患者根据是否合并MS分为MS组(163例)和非MS组(119例),测定24h尿白蛋白(UAlb)及相关生化指标,比较两组UAlb水平及糖尿病肾病(DN)患病率,采用多元Logistic回归方法分析T2DM患者微量白蛋白尿的危险因素。结果:MS组的UAlb及DN患病率明显高于非MS组,且随着MS组分增加,UAlb水平显著升高。多元Logistic回归分析表明甘油三酯、糖化血红蛋白、收缩压为影响UAlb的独立危险因素。结论:T2DM患者微量白蛋白尿与MS密切相关,需采取综合干预措施避免或延缓DN的发生发展。     

代谢综合征患者血液流变学及多因素相关分析

目的:探讨代谢综合征(MS)患者血液流变学及多因素的相关性。方法:检测49例2型糖尿病(T2DM)和40例MS患者的肥胖指标、血脂、血黏度,并进行比较和相关性分析。结果:(1)MS组的BMI(体重指数),FAT%(体脂百分率),W(腰围),LP(脂蛋白),TG(甘油三酯),TC(总胆固醇),血浆黏度均显著高于T2DM组(p＜0．05);(2)T2DM组的血浆黏度与TC及MS组的W与BMI,FAT%正相关(p＜0．05)。结论:(1)MS较T2DM存在更高的血浆黏度,可能是多因素综合作用的结果。(2)FAT%的测定对中心性肥胖的评估具有一定意义。     

饮食诱导代谢综合征小鼠模型的建立

目的建立以高脂纯化饲料诱导的、遗传背景和环境因素共同起作用的C57BL/6J小鼠代谢综合征（MS）模型,为研究营养因素与代谢综合征的关系提供周期较短、稳定性好、可重复性、与人类发病可比性高的动物模型。方法雄性3周龄C57BL/6J小鼠30只适应性喂养10d后随机分为2组,其中一组（10只）给予普通生长饲料（对照组）,另一组（20只）给予高脂纯化饲料（模型组）。喂养期间对空腹血糖（FBG）、体重进行连续监测,同时监测体重指数（BMI）、血清胰岛素（FINS）、血清甘油三脂（TG）、总胆固醇（TC）、高密度脂蛋白（HDL-C）、低密度脂蛋白（LDL-C）,实验期10周。实验结束时取内脏脂肪和肝脏称重,取肝胰做病理分析。结果分组喂养1周时,模型组小鼠体重出现显著性升高（P〈0.001）,并表现为中心型肥胖。4周时FBG显著性升高（P〈0.05）,5周时FINS开始升高但无显著性差异。8周时血清TC、HDL-C显著性升高（P〈0.001）,10周时TG、TC、HDL-C、LDL-C均升高（P〈0.01）。HE染色显示肝脏中度脂肪变,胰岛细胞无明显改变。结论单纯施以高脂饲料10周即可建立MS小鼠模型。并且该模型造模方法简单易行、周期较短、稳定性好、可重复性高,与人类MS自然发病过程类似,是MS较理想的动物模型。     

Sleep and circadian rhythms: key components in the regulation of energy metabolism

In this review, we present evidence from human and animal studies to evaluate the hypothesis that sleep and circadian rhythms have direct impacts on energy metabolism, and represent important mechanisms underlying the major health epidemics of obesity and diabetes. The first part of this review will focus on studies that support the idea that sleep loss and obesity are "interacting epidemics." The second part will discuss recent evidence that the circadian clock system plays a fundamental role in energy metabolism at both the behavioral and molecular levels. These lines of research must be seen as in their infancy, but nevertheless, have provided a conceptual and experimental framework that potentially has great importance for understanding metabolic health and disease.     

GENE-GENE INTERACTION BETWEEN SEROTONIN TRANSPORTER (SLC6A4) AND CLOCK MODULATES THE RISK OF METABOLIC SYNDROME IN ROTATING SHIFTWORKERS

Serotonergic neurotransmission and the master circadian CLOCK gene are physiological modulators of the circadian system. In addition, both are involved in the physiopathology of metabolic syndrome (MS). The authors sought to examine the potential effect of the gene-gene interaction between the functional 44-bp insertion/deletion polymorphism in the promoter region (serotonin-transporter-linked promoter region polymorphism or 5-HTTLPR) of the serotonin transporter gene (SLC6A4) and common variants of the gene CLOCK on the genetic risk underlying MS of shift-workers. To test this hypothesis, 856 men were studied; 518 dayworkers were compared with 338 rotating shiftworkers. Medical history, health examination including anthropometric and arterial blood pressure measurements, a questionnaire on health-related behaviors, and biochemical determinations were obtained from every participant. 5-HTTLPR genotypes were determined using polymerase chain reaction followed by gel electrophoresis. Six tag single-nucleotide polymorphisms (SNPs) in the CLOCK gene with a minor allele frequency >10 % (rs1554483 C/G, rs11932595 A/G, rs4580704 C/G, rs6843722 A/C, rs6850524 C/G, and rs4864548 A/G), encompassing 117 kb of chromosome 4 and representing 115 polymorphic sites (r²?>?.8), were genotyped. A significant interaction between the 5-HTTLPR variant and the haplotype rs1554483–rs4864548 of the CLOCK gene was detected for diastolic (p?=?.0058) and systolic blood pressure (p?=?.0014), arterial hypertension (p?=?.033), plasma triglycerides levels (p?=?.033), and number of MS components (p?=?.01). In all these cases, the higher values were observed in rotating shiftworkers homozygous for the SLC6A4 S allele and carrying the haplotype composed by the CLOCK rs1554483 G and rs4864548 A variants. In conclusion, these data suggest a potential interaction (epistatic effect) of serotonin transporter and CLOCK gene variation on the genetic susceptibility to develop MS by rotating shiftworkers. (Author correspondence: cpirola@ciudad.com.ar or pirola.carlos@lanari.fmed.uba.ar)     

Alcohol Consumption Patterns of Shiftworkers Compared With Dayworkers

The detrimental effects of excessive alcohol consumption are well documented. There is some evidence that shiftworkers consume more alcohol than dayworkers as a sleep aid to compensate for sleep difficulties associated with work schedules. This study investigated drinking patterns between shiftworkers and dayworkers using the 2006 and 2007 waves from the Household Income and Labour Dynamics Survey. A subset of workers who were not in full-time study and had a single job were selected; participants who did not drink alcohol (n?=?2090) were excluded. Using the 2001 Australian Government alcohol guidelines, alcohol consumption for risk of short-term harm (7+ standard drinks for men, 5+ for women) was investigated. The number of workers who drank alcohol “nearly every day” or “every day” was also examined. Some 13% of shiftworkers and 10% of those on standard schedules reported consuming alcohol at levels risky for short-term harm. Having a child less than 17 yrs (odds ratio [OR]?=?.39, 95% confidence interval [CI]?=?.22–.69), higher job demands (OR?=?.71, 95% CI?=?.58–.86), being female (OR?=?.45, 95% CI=. 26–.79), and being older (OR?=?.89, 95% CI?=?.87–.92) significantly reduced, whereas being a shiftworker (OR?=?2.10, 95% CI?=?1.08–4.12) significantly increased, the odds of drinking alcohol in short-term risky levels. Nearly 10% of shiftworkers and 8% of those on standard schedules reported consuming alcohol in short-term risky levels at least weekly. Having a child less than 17 yrs (OR?=?.40, 95% CI?=?.22–.74), higher job demands (OR?=?.69, 95% CI?=?.56–.86), being female (OR?=?.28, 95% CI?=?.15–.53), and being older (OR?=?.92, 95% CI?=?.89–.94) were associated with a significant reduction in the odds of consuming alcohol at risky levels at least weekly. Being a shiftworker was not associated with a significant increase in the odds of consuming alcohol at such risky levels at least weekly, but a trend was evident (OR?=?1.47, 95% CI?=?.73–3.00). Some 13.5% of shiftworkers and 21% of those on standard schedules reported consuming alcohol in any amount “near daily” or “daily.” Working more hours than preferred (OR?=?1.80, 95% CI?=?1.12–2.89) and being older (OR?=?1.10, 95% CI?=?1.07–1.13) were associated with a significant increase, and being female (OR?=?.18, 95% CI?=?.10–.33), and being a shiftworker (OR?=?.20, 95% CI?=?.09–.45) were associated with a significant decrease in the odds of consuming alcohol “daily” or “near daily.” Overall, the results suggest that shiftworkers may be more likely to consume alcohol at levels considered to be risky for health in the short term. In contrast, they appear less likely to drink alcohol daily. This pattern is suggestive of “binge drinking” behavior. (Author correspondence: jill.dorrian@unisa.edu.au)     

Effects of Lifetime Exposure to Shiftwork on Fitness for Duty in Police Officers

Aging and demographic changes in Europe and other global economies have led to a discussion about postponing the legal retirement age; however, health and safety consequences for the workforce have not yet been examined. Thus, the aim of this study was to investigate the effects of lifetime exposure to shiftwork on health impairments and fitness for duty. Two samples of the police force from one of the states of the Federal Republic of Germany were used. One sample was collected in 2008–2009 with a self-administered Internet questionnaire (n?=?705); the other sample was derived from employment records provided by the police force of the same federal state for the years 2002–2009 (n?=?2460). Both samples contained information about the number of years worked in shiftwork across the entire working life and impairments to fitness for duty assessed by occupational physicians. Thus, the number of years of shiftwork until the diagnosis of the first reduction in fitness for duty could be calculated. Survival analyses were performed to estimate the risk (hazard rate) for experiencing a reduction in fitness for duty across lifetime exposure to shiftwork in years, controlling for age, sex, work type, and police district. Hazard estimates were compared across both samples to cross-validate the results. The findings indicated an increase in the risk of reduced fitness for duty with increasing number of years in shiftwork during the working life in both samples. The hazard rates followed an exponential trend, indicating a rapid increase in health impairments in particular beyond 20 yrs of shiftwork. These findings were consistent in both samples, collected with different methods and over different time periods, thus indicating high validity. Therefore, occupational stress factors, such as exposure to shiftwork, need to be taken into account when discussing the postponement of the legal retirement age. (Author correspondence: anna.wirtz@gawo-ev.de)