Do holidays change subjective sleep length or sleep debt in shift work disorder?

In shift work disorder (SWD), disturbed sleep acutely impairs employees' recovery, but little attention has been paid to sleep during longer recovery periods. We examined how holidays affect self-estimated sleep length, sleep debt, and recovery in cases of SWD. Twenty-one shift workers with questionnaire-based SWD and nine reference cases without SWD symptoms completed a questionnaire on recovery and sleep need. They also reported sleep length on two separate occasions: during a work period and after ≥ 2 weeks of holidays. Sleep debt was calculated by subtracting sleep length from sleep need. We used parametric tests to compare the groups and the periods. The groups reported shorter sleep on workdays than during holidays (median difference: SWD group 1.7 h, p<0.001; reference group 1.5 h; p<0.05). The SWD group's self-estimated sleep during holidays increased less above the sleep need (median 0.0 h) than the reference group's sleep (1.0 h, p<0.05). In addition, the SWD group reported good recovery from irregular working hours less often (14%) than the reference group (100%, p<0.001). Although holidays were generally associated with longer sleep estimates than workdays, employees with SWD experienced consistently less efficient recovery than those without SWD.

Differential DNA methylation in recovery from shift work disorder.

The human DNA methylome is responsive to our environment, but its dynamics remain underexplored. We investigated the temporal changes to DNA methylation (DNAme) in relation to recovery from a shift work disorder (SWD) by performing a paired epigenome-wide analysis in an occupational cohort of 32 shift workers (25 men, age = 43.8 ± 8.8 years, 21 SWD cases). We found that the effect of vacation on DNAme was more prominent in the SWD-group as compared to controls, with respect to the amount of significantly differentially methylated positions (DMPs; Punadj < 0.05) 6.5 vs 3.7%, respectively. The vast majority (78%) of these DMPs were hypomethylated in SWD but not in controls (27%) during the work period. The Gene Ontology Cellular component "NMDA glutamate receptor" (PFDR < 0.05) was identified in a pathway analysis of the top 30 genes in SWD. In-depth pathway analyses revealed that the Reactome pathway "CREB phosphorylation through the activation of CaMKII" might underlie the recovery. Furthermore, three DMPs from this pathway, corresponding to GRIN2C, CREB1, and CAMK2B, correlated with the degree of recovery (Punadj < 0.05). Our findings provide evidence for the dynamic nature of DNAme in relation to the recovery process from a circadian disorder, with biological relevance of the emerging pathways.

High need for recovery from work and sleep problems are associated with workers' unhealthy dietary habits.

OBJECTIVE: We aimed to examine the association of recovery from work and sleep with workers' dietary habits. DESIGN: Cross-sectional study. Need for recovery (NFR) from work was assessed with a validated questionnaire. Sleep was assessed with five questions from the Nordic Sleep Questionnaire and sleep quality question. Dietary habits were estimated using a validated sixteen food groups-containing questionnaire. Ordered logistic regression was used to explore the associations of NFR and sleep with dietary habits adjusted for age, education, marital status, work schedule, working full or part time and occupation. SETTING: Follow-up visits of type 2 diabetes prevention study cohort in a Finnish airline company. PARTICIPANTS: The study included 737 men and 605 women. RESULTS: Poor recovery from work was associated with a higher eating frequency (OR = 1·03, 95 % CI 1·00, 1·06), higher intake of fast food (OR = 1·05, 95 % CI 1·02, 1·08) and sweets (OR = 1·05, 95 % CI 1·02, 1·08) as well as lower intake of vegetables (OR = 0·96, 95 % CI 0·93, 0·98) and fruits (OR = 0·96, 95 % CI 0·93, 0·98) among men. In women, poor recovery from work was associated with higher fast food (OR = 1·06, 95 % CI 1·02, 1·09) and desserts consumption (OR = 1·04, 95 % CI 1·00, 1·07). Among men and women, sleep problems were associated with higher eating frequency (men: OR = 1·04, 95 % CI 1·00, 1·07, women: OR = 1·06, 95 % CI 1·02, 1·11), consumption of fast food (men: OR = 1·07, 95 % CI 1·04, 1·11, women: OR = 1·06, 95 % CI 1·02, 1·10) and sweets (men: OR = 1·05, 95 % CI 1·01, 1·08, women: OR = 1·04, 95 % CI 1·00, 1·08). CONCLUSIONS: Poor recovery from work and sleep problems were associated with unfavourable dietary habits especially in men.

The association of work stress and night work with nutrient intake - a prospective cohort study.

Objectives In a prospective study among workers in an airline company, we explored whether change in work stress symptoms or night shifts was associated with nutrient intake. Methods Participants in a workplace type 2 diabetes (T2D) prevention study completed a questionnaire on lifestyle, work stress symptoms, work schedule, and food intake at baseline and after 2.4-years follow-up (211 men and 155 women, 93% with increased risk for T2D). Multiple linear regression models with covariates were used to explore the associations between change in work stress symptoms or night shifts and change in nutrient intake during the follow-up. Results Among men, an increase in stress and a decrease in perceived workability was associated with a higher proportion of energy (E%) from fat [ß 0.6, 95% confidence interval (CI) 0.07-1.11, ß 1.3, 95% CI 0.57-2.05] and saturated fat (ß 0.3, 95% CI 0.02-0.58, ß 0.5, 95% CI 0.14-0.90), respectively. Furthermore, a decrease in workability was associated with lower vitamin C intake (ß-9.2, 95% CI -16.56- -1.84) and an increase in sleepiness with higher E% from saturated fat (ß 0.7, 95% CI 0.00-0.15). Among women, an increase in work-related fatigue was associated with higher alcohol intake (ß 7.5, 95% CI 1.25-13.74) and an increase of night shifts was associated with higher E% from fat (ß 0.24, 95% CI 0.00-0.47) and saturated fat (ß 0.17, 95% CI 0.04-0.29). Conclusions Work stress symptoms were associated with a reduction in diet quality especially among men. The possible impact of work stress symptoms on workers' dietary habits should be acknowledged and the assessment of dietary habits should consequently be incorporated into occupational health examinations.

A distinctive DNA methylation pattern in insufficient sleep.

Short sleep duration or insomnia may lead to an increased risk of various psychiatric and cardio-metabolic conditions. Since DNA methylation plays a critical role in the regulation of gene expression, studies of differentially methylated positions (DMPs) might be valuable for understanding the mechanisms underlying insomnia. We performed a cross-sectional genome-wide analysis of DNA methylation in relation to self-reported insufficient sleep in individuals from a community-based sample (79 men, aged 39.3 ± 7.3), and in relation to shift work disorder in an occupational cohort (26 men, aged 44.9 ± 9.0). The analysis of DNA methylation data revealed that genes corresponding to selected DMPs form a distinctive pathway: "Nervous System Development" (FDR P value < 0.05). We found that 78% of the DMPs were hypomethylated in cases in both cohorts, suggesting that insufficient sleep may be associated with loss of DNA methylation. A karyoplot revealed clusters of DMPs at various chromosomal regions, including 12 DMPs on chromosome 17, previously associated with Smith-Magenis syndrome, a rare condition comprising disturbed sleep and inverse circadian rhythm. Our findings give novel insights into the DNA methylation patterns associated with sleep loss, possibly modifying processes related to neuroplasticity and neurodegeneration. Future prospective studies are needed to confirm the observed associations.

Sleep and alertness in shift work disorder: findings of a field study.

PURPOSE: Although shift work disorder (SWD) affects a major part of the shift working population, little is known about its manifestation in real life. This observational field study aimed to provide a detailed picture of sleep and alertness among shift workers with a questionnaire-based SWD, by comparing them to shift workers without SWD during work shifts and free time. METHODS: SWD was determined by a questionnaire. Questionnaires and 3-week field monitoring, including sleep diaries, actigraphy, the Karolinska Sleepiness Scale (KSS), EEG-based sleep recordings, and Psychomotor Vigilance Tasks (PVT), were used to study 22 SWD cases and 9 non-SWD workers. RESULTS: The SWD group had a shorter subjective total sleep time and greater sleep debt before morning shifts than the non-SWD group. Unlike the non-SWD group, the SWD group showed little compensatory sleep on days off. The SWD group had lower objective sleep efficiency and longer sleep latency on most days, and reported poorer relaxation at bedtime and sleep quality across all days than the non-SWD group. The SWD group's average KSS-sleepiness was higher than the non-SWD group's sleepiness at the beginning and end of morning shifts and at the end of night shifts. The SWD group also had more lapses in PVT at the beginning of night shifts than the non-SWD group. CONCLUSIONS: The results indicate that SWD is related to disturbed sleep and alertness in association with both morning and night shifts, and to less compensatory sleep on days off. SWD seems to particularly associate with the quality of sleep.

Common Genetic Variation Near Melatonin Receptor 1A Gene Linked to Job-Related Exhaustion in Shift Workers.

Study Objectives: Tolerance to shift work varies; only some shift workers suffer from disturbed sleep, fatigue, and job-related exhaustion. Our aim was to explore molecular genetic risk factors for intolerance to shift work. Methods: We assessed intolerance to shift work with job-related exhaustion symptoms in shift workers using the emotional exhaustion subscale of the Maslach Burnout Inventory-General Survey, and carried out a genome-wide association study (GWAS) using Illumina's Human610-Quad BeadChip (n = 176). The most significant findings were further studied in three groups of Finnish shift workers (n = 577). We assessed methylation in blood cells with the Illumina HumanMethylation450K BeadChip, and examined gene expression levels in the publicly available eGWAS Mayo data. Results: The second strongest signal identified in the GWAS (p = 2.3 × 10E-6) was replicated in two of the replication studies with p < .05 (p = 2.0 × 10E-4 when combining the replication studies) and indicated an association of job-related exhaustion in shift workers with rs12506228, located downstream of the melatonin receptor 1A gene (MTNR1A). The risk allele was also associated with reduced in silico gene expression levels of MTNR1A in brain tissue and suggestively associated with changes in DNA methylation in the 5' regulatory region of MTNR1A. Conclusions: These findings suggest that a variant near MTNR1A may be associated with job-related exhaustion in shift workers. The risk variant may exert its effect via epigenetic mechanisms, potentially leading to reduced melatonin signaling in the brain. These results could indicate a link between melatonin signaling, a key circadian regulatory mechanism, and tolerance to shift work.

Food and nutrient intake among workers with different shift systems.

OBJECTIVES: Over 20% of employees in Europe work in shifts. Shift work increases the risk for chronic diseases, but a healthy lifestyle may attenuate the adverse effect of shift work. The aim of this study was to explore food and nutrient intake differences between working time groups. METHODS: The participants were 1478 employees (55% of men) of an airline divided into three working time groups: day work (n=608), shift work without in-flight work (n=541) and in-flight work (n=329). Measures included laboratory tests, physical measurements, a questionnaire, and food and nutrient intake estimations by a validated 16-item food intake questionnaire. RESULTS: Shift working men were less likely to consume vegetables (p<0.001) and fruits (p=0.049) daily than male day and in-flight workers. In women, energy intake from saturated fat was higher among shift workers compared with day workers (12.6 vs 12.2 E%, p=0.023). In older female participants, energy intake from fat and saturated fat was higher in the shift work and in-flight work groups than in the day work group (p<0.001). CONCLUSIONS: In this study, shift work and working environment were associated with dietary habits, and this association was not explained by other characteristics such as workers' educational level. Shift workers' increased risk for chronic diseases should be taken into account and lifestyle counselling including advice in nutrition should be incorporated in routine occupational healthcare of shift workers.

Prevention of diabetes and cardiovascular diseases in occupational health care: feasibility and effectiveness.

AIMS: To evaluate feasibility and effectiveness of lifestyle counseling in occupational setting on decreasing risk for diabetes and cardiovascular disease. METHODS: A health check-up including physical examination, blood tests, questionnaires and health advice was completed on 2312 employees of an airline company. Participants with elevated risk for type 2 diabetes based on FINDRISC score and/or blood glucose measurement (n=657) were offered 1-3 additional lifestyle counseling sessions and 53% of them agreed to participate. After 2.5 years, 1347 employees of 2199 invited participated in a follow-up study. RESULTS: Among women and men with low baseline diabetes risk, cardiovascular risk factors increased slightly during follow-up. Larger proportion of the men who attended interventions lost weight at least 5% compared with the non-attendees (18.4% vs. 8.4%, p=0.031) and their FINDRISC score increased less (0.6 vs. 1.5, p=0.037). Older age associated with participation in follow-up and higher baseline FINDRISC score and presence of clinical and lifestyle risk factors and problems in sleep and mood increased attendance in interventions. CONCLUSIONS: Identification of employees with cardiovascular and diabetes risk, and the low intensity lifestyle intervention were feasible in occupational health-care setting. However, the health benefits were modest and observed only for men with increased risk.

Shift rotation and age - interactions with sleep-wakefulness and inflammation.

The interaction of age with shift rotation in relation to sleep-wakefulness and inflammation were studied among male employees (n = 772). Cross-sectional analyses in day, two-shift and three-shift work with different shift rotations, as well as changes in leukocytes and hsCRP among three shift workers who changed their shift system during the 2.5- yr follow-up were completed. Shift work was associated with problems to fall asleep (p < 0.001) and feeling of the current working time being harmful to sleep and wakefulness (p < 0.001). Quickly forward-rotation shift workers considered their working time less harmful compared with slower backward-rotation shift workers. Age did not influence sleep in general, but older workers in the quickly forward-rotating three-shift system had less sleep complaints than their younger colleagues. The age differences in the inflammatory markers partly depended on the shift system. The results give some support that rapidly forward-rotating shift systems are more 'age-friendly' than backward-rotating shift systems.

A simple tool for diet evaluation in primary health care: validation of a 16-item food intake questionnaire.

Our aim was to validate a 16-item food intake questionnaire (16-FIQ) and create an easy to use method to estimate patients' nutrient intake in primary health care. Participants (52 men, 25 women) completed a 7-day food record and a 16-FIQ. Food and nutrient intakes were calculated and compared using Spearman correlation. Further, nutrient intakes were compared using kappa-statistics and exact and opposite agreement of intake tertiles. The results indicated that the 16-FIQ reliably categorized individuals according to their nutrient intakes. Methods to estimate nutrient intake based on the answers given in 16-FIQ were created. In linear regression models nutrient intake estimates from the food records were used as the dependent variables and sum variables derived from the 16-FIQ were used as the independent variables. Valid regression models were created for the energy proportion of fat, saturated fat, and sucrose and the amount of fibre (g), vitamin C (mg), iron (mg), and vitamin D (µg) intake. The 16-FIQ is a valid method for estimating nutrient intakes in group level. In addition, the 16-FIQ could be a useful tool to facilitate identification of people in need of dietary counselling and to monitor the effect of counselling in primary health care.

Genome-wide scan of job-related exhaustion with three replication studies implicate a susceptibility variant at the UST gene locus.

Job-related exhaustion is the core dimension of burnout, a work-related stress syndrome that has several negative health consequences. In this study, we explored the molecular genetic background of job-related exhaustion. A genome-wide analysis of job-related exhaustion was performed in the GENMETS subcohort (n = 1256) of the Finnish population-based Health 2000 study. Replication analyses included an analysis of the strongest associations in the rest of the Health 2000 sample (n = 1660 workers) and in three independent populations (the FINRISK population cohort, n = 10 753; two occupational cohorts, total n = 1451). Job-related exhaustion was ascertained using a standard self-administered questionnaire (the Maslach Burnout Inventory (MBI)-GS exhaustion scale in the Health 2000 sample and the occupational cohorts) or a single question (FINRISK). A variant located in an intron of UST, uronyl-2-sulfotransferase (rs13219957), gave the strongest statistical evidence in the initial genome-wide study (P = 1.55 × 10(-7)), and was associated with job-related exhaustion in all the replication sets (P < 0.05; P = 6.75 × 10(-7) from the meta-analysis). Consistent with studies of mood disorders, individual common genetic variants did not have any strong effect on job-related exhaustion. However, the nominally significant signals from the allelic variant of UST in four separate samples suggest that this variant might be a weak risk factor for job-related exhaustion. Together with the previously reported associations of other dermatan/chondroitin sulfate genes with mood disorders, these results indicate a potential molecular pathway for stress-related traits and mark a candidate region for further studies of job-related and general exhaustion.

Occupational health care identifies risk for type 2 diabetes and cardiovascular disease.

AIMS: To assess the risk for type 2 diabetes (T2D) and cardiovascular disease (CVD) among employees of a Finnish airline; to study the association of shift work with T2D and CVD risk; and to test the feasibility of risk screening in occupational health care setting. METHODS: Altogether 4169 employees were invited for a health check-up and 2312 participated in this study. The check-up included physical examinations, questionnaires on working hours, sleep, and lifestyle, diabetes risk score FINDRISC, and blood tests. Lifestyle counselling was offered for those with increased T2D risk. RESULTS: Altogether 15% of participants had a high T2D risk (FINDRISC≥15 and/or elevated, but non-diabetic blood glucose), and a further 15% had a moderate T2D risk (FINDRISC 10-14 and normal blood glucose). Of those 60% agreed to attend lifestyle counselling. Metabolic syndrome was more common, lipid profile more unfavorable and hsCRP higher by increasing FINDRISC score category. Risk factor profiles linked to shift work status were not self-evident. CONCLUSIONS: The renewed health check-up process effectively identified those employees with increased T2D and CVD risk who would benefit from lifestyle intervention. The use of FINDRISC questionnaire was a feasible first-step screening method in occupational health care setting.

The relationship between current and former shift work and the metabolic syndrome.

OBJECTIVE: The occurrence of possible health hazards among former shift workers is not well-known. We studied associations of former and current shift work with the metabolic syndrome (MetS). METHODS: Participants were 1811 full-time employees of a large airline company (1009 men). Working times were categorized into five groups: day worker [N=297 (the reference group)], former shift worker (N=341), 2-shift worker (N=418), night-shift worker (N=283), and in-flight worker (N=472). MetS was measured by the International Diabetes Federation (IDF) criteria and the National Institute of Health Adult Treatment Panel III (NCEP) guideline. The prevalence of the syndrome in the study population was 28.5% and 20.8%, respectively. RESULTS: Among male former shift workers, MetS was more prevalent compared to male day workers [IDF: age-adjusted odds ratio (OR) 2.13, 95% confidence interval (95% CI) 1.35-3.37; NCEP: OR 1.83, 95% CI 1.13-2.96]. Associations did not change after additional adjustments for education, smoking, physical activity, alcohol consumption, and insomnia symptoms (IDF: OR 2.00, 95% CI 1.26-3.19; NCEP: 1.67, 95% CI 1.02-2.72). Male 2-shift workers also had an elevated risk of IDF-defined MetS (OR 1.64, 95% CI 1.06-2.55) but the association weakened in the fully adjusted analyses (OR 1.48, 95% CI 0.93-2.24). Prevalence of the MetS was marginally significantly higher among night-shift work (IDF: OR 1.51, 95% CI 0.95-2.34) and was attenuated further with additional adjustments (OR 1.37, 95% CI 0.84-2.22). Among women, no significant differences in prevalence of the MetS between day work and shift work were observed. CONCLUSION: Findings of the cross-sectional study suggest that MetS diagnosed by standardized criteria is more prevalent among former male shift workers than current day workers who have never worked in shifts.

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.

Effects of shift rotation and the flexibility of a shift system on daytime alertness and cardiovascular risk factors.

OBJECTIVES: A controlled intervention study was conducted to evaluate the effects of two changes in shift characteristics on alertness and cardiovascular risk factors: a change in shift rotation (direction and speed) and a change in the flexibility of the shift system. METHODS: Altogether 84 male workers currently working in a backward-rotating shift system volunteered for the study. A total of 40 men changed to a rapidly forward-rotating shift system, 22 changed to a more flexible shift system, and 22 remained with the old shift system. Health effects were studied with the use of clinical measurements, blood tests, and questionnaires before and after the shift changes. Analyses of variance were used with repeated measures to study associations of cardiovascular risk factors and daytime sleepiness according to the change in shift systems. RESULTS: The mean number of days on which the workers reported sleepiness decreased in the group with the forward-rotating shift system when compared with that of the group on the old shift system (from 2.9 to 2.1 days/week, P=0.02). Systolic blood pressure decreased (from 142 to 136 mm Hg, P=0.049), and heart rate showed a declining trend (from 66 to 60 beats/minute, P=0.06) in the flexible shift system when the three groups were compared. CONCLUSIONS: The study indicates that a faster speed, together with a change to the forward direction, in shift rotation alleviates daytime sleepiness. Combining individual flexibility with company-based flexibility in a shift system may have favorable effects on shift workers' blood pressure.