Sleep duration and quality in permanent night work: an observational field study.

PURPOSE: Permanent night workers conceivably show better adaptation of circadian rhythms to night work than shift workers and therefore better possibilities of obtaining sufficient sleep of good quality after night shifts. We investigated the effect of night shifts including number of consecutive shifts on sleep among self-selected permanent night workers, and studied if the effect of night shifts differed between morning and evening types and compared with 3-shift workers. METHODS: The study population included 90 permanent night workers followed for 14 days (warehouse workers, 1228 observation days, 80% males). For comparison, we included 70 3-shift workers followed for 26 days (police officers, 1774 observation days, 100% men). Total sleep time (TST), primary sleep duration (PSD), and sleep efficiency were assessed by actigraphy. Measures of sleep quality and diurnal type were self-reported. RESULTS: Among permanent night workers, TST, PSD, difficulties falling asleep, disturbed sleep, and the number of awakenings decreased after night shifts compared with days without night work. Sleep efficiency, difficulties awakening, and non-refreshing sleep increased. More consecutive night shifts were associated with shorter TST and PSD. Sleep outcomes did not differ by diurnal type. Permanent night workers had fewer awakenings after night shifts than 3-shift workers, but no other differences were observed. CONCLUSION: This study does not provide evidence that supports recommendation of permanent night work to reduce adverse effects of night shifts on sleep. A limited number of consecutive night shifts is recommended to reduce accumulation of sleep debt.

History of working conditions and the risk of old-age dependency: a nationwide Swedish register-based study.

AIMS: There is substantial evidence that previous working conditions influence post-retirement health, yet little is known about previous working conditions' association with old-age dependency. We examined job strain, hazardous and physical demands across working life, in relation to the risk of entering old-age dependency of care. METHODS: Individually linked nationwide Swedish registers were used to identify people aged 70+ who were not receiving long-term care (residential care or homecare) at baseline (January 2014). Register information on job titles between the years 1970 and 2010 was linked with a job exposure matrix of working conditions. Random effects growth curve models were used to calculate intra-individual trajectories of working conditions. Cox regression models with age as the timescale (adjusted for living situation, educational attainment, country of birth, and sex) were conducted to estimate hazard ratios for entering old-age dependency during the 24 months of follow-up (n = 931,819). RESULTS: Having initial adverse working conditions followed by an accumulation throughout working life encompassed the highest risk of entering old-age dependency across the categories (job strain: HR 1.23, 95% CI 1.19-1.27; physical demands: HR 1.36, 95% CI 1.31-1.40, and hazardous work: HR 1.35, 95% CI 1.30-1.40). Initially high physical demands or hazardous work followed by a stable trajectory, or initially low-level physical demand or hazardous work followed by an accumulation throughout working life also encompassed a higher risk of dependency. CONCLUSIONS: A history of adverse working conditions increased the risk of old-age dependency. Reducing the accumulation of adverse working conditions across the working life may contribute to postponing old-age dependency.

Does it matter for health if steps are taken during work or leisure? A prospective accelerometer study using register-based long-term sickness absence.

BACKGROUND: Walking is known to be good for health. However, it is unknown whether it matters if steps are taken during work or leisure. Therefore, we aimed to examine the prospective association between accelerometer-measured steps taken during work or leisure and register-based long-term sickness absence (LTSA). METHODS: We included 937 blue- and white-collar workers from the PODESA cohort who wore a thigh-based accelerometer over four days to measure number of steps during work and leisure. Steps were divided into domain based on diary data. First event of LTSA was retrieved from a national register with four years' follow-up. We used Cox proportional hazard models to analyze the association between domain-specific and total daily steps and LTSA, adjusted for age, sex, job type, smoking, and steps in the other domain (e.g., work/leisure). RESULTS: We found more steps at work to be associated with a higher LTSA risk [Hazard Ratio (HR):1.04; 95% CI: 1.00-1.08 per 1000 steps]. No significant association was found between steps during leisure and LTSA (HR: 0.97; 95% CI: 0.91-1.02), nor between total daily steps and LTSA (HR: 1.01; CI 95% 0.99-1.04). CONCLUSIONS: More steps at work were associated with higher risk of LTSA, while steps during leisure was not clearly associated with LTSA risk. These findings partly support 'the physical activity paradox' stating that the association between physical activity and health depends on the domain.

Heart rate variability during sleep after two, four and seven consecutive night shifts and recovery days: a cross-over intervention study.

OBJECTIVE: Recovery after shift work is an important part reducing the health problems related to shift work. Heart rate variability (HRV) is an indicator of the balance between sympathetic and parasympathetic activity in the autonomic nervous system and can be used as a measure of recovery after night shifts. The aim of the study is to investigate autonomic recovery during sleep in response to night work in a crossover intervention study. METHODS: Seventeen male police officers working in call centres in five different police district participated in the HRV measurements. The participants were exposed to three interventions: 2 + 2: two consecutive night shifts followed by two consecutive day recovery days; 4 + 4: four consecutive night shifts followed by four consecutive recovery days; 7 + 7: seven consecutive night shifts followed by seven consecutive recovery days. On the last day with night shift and the last recovery day in each intervention the participants underwent 24 h HRV recordings. We analysed HRV during sleep. The five 5-min intervals with the lowest heart rate during each sleep period were chosen for spectral analysis of the heart interbeat interval time series. The five 5-min intervals could occur at any time during sleep. RESULTS: There were overall differences in HRV during sleep between days with night shifts and recovery days, primarily in parasympathetic activity. There was no difference in the lowest heart rate obtained, but the timing was different for the three interventions. The lowest heart rate after night shifts occurred 112 (SD 79) min, 174 (SD 115) min and 135 (SD 94) min after sleep onset for the 2 + 2 night shift, the 4 + 4 night shift and the 7 + 7 night shift, respectively. CONCLUSION: Overall sleep-related autonomic recovery had higher parasympathetic modulation of cardiac rhythm on the 2 + 2 shift system compared to the 4 + 4 and 7 + 7 shift system.

How Risk Management During COVID-19 Influences Eldercare Personnel's Perceptions of Their Work Environment.

OBJECTIVE: To investigate the association between workplace COVID-19 (coronavirus disease 2019) risk management and eldercare workers' perception of their social environment at work. METHODS: Cross-sectional questionnaire data from 952 participants were collected by the Danish labor union, FOA, and analyzed using multinomial logistic regression. RESULTS: Unclear guidelines, insecurity regarding organization of work, lack of attention to vulnerable employees, and lack of instruction in the use of personal protective equipment were associated with perceived negative changes in the social environment at work. Also, higher local incidence rates of SARS-CoV-2 infections were associated with a weaker sense of community (odds ratio, 1.18; 95% confidence interval, 1.04-1.36). CONCLUSIONS: These findings indicate that risk management is important not only for prevention of infection but also for individual and workplace resilience toward external demands and health threats.

Educational attainment in young adulthood and self-rated health in midlife - Does allostatic load mediate the association?

This study aimed to examine the extent to which allostatic load (AL), measured in midlife, mediates the association between educational attainment in young adulthood and self-rated health (SRH) in midlife among women and men. The study used data from the Copenhagen Aging and Midlife Biobank (CAMB; n = 5467 participants, aged 48-62 years, 31.5% women). Educational attainment was assessed as years of education. SRH was assessed with one item: 'In general, how would you say your health is?' with response options from "excellent" to "poor". AL mediated 31.7% and 19.7% of the association between educational attainment and SRH in women and men, respectively. We observed that higher educational attainment was associated with better SRH and lower AL in both women and men. Our study showed that AL partly mediates the association between educational attainment in young adulthood and SRH in adulthood among both men and women. This study indicates that educational attainment in young adulthood affects health throughout life. Such knowledge of a potential mediator may be important in breaking the social heritage.

The role of combined modifiable lifestyle behaviors in the association between exposure to stressors and allostatic load: A systematic review of observational studies.

BACKGROUND: Exposure to stressors can evoke psychological, physiological, and behavioral stress responses, which may lead to the adoption of health-damaging behaviors that dysregulate multiple biological systems contributing to a high allostatic load. This review explored the role of combined modifiable lifestyle behaviors in the relationship between stressors and allostatic load among healthy adults. METHODS: A systematic search was conducted in Medline Complete, PsycINFO, CINAHL, and Embase databases up to September 2021. The PRISMA guidelines guided reporting and study quality was assessed using the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Checklist. RESULTS: Database searches identified 319 papers. Eight cross-sectional and two longitudinal studies met our inclusion criteria. Among the ten studies, combined modifiable lifestyle behaviors partly explained the association between exposure to stressors and elevated allostatic load in four cross-sectional and two longitudinal studies. CONCLUSION: Some evidence suggests that combined modifiable lifestyle behaviors may help explain the relationship between stressors and an elevated allostatic load. Further longitudinal studies with mediation analyses would strengthen these findings and help to confirm the mechanistic role of combined modifiable lifestyle behaviors underlying the relationship between stress exposure and allostatic load.

The effect of COVID-19 on schoolteachers' emotional reactions and mental health: longitudinal results from the CLASS study.

PURPOSE: We investigated schoolteachers' emotional reactions to COVID-19 and mental health during three phases of the COVID-19 pandemic. We further analyzed if teachers, who belonged to a COVID-19 risk group, had more emotional reactions and poorer mental health than "non-risk" groups. METHODS: We collected questionnaire data in May, June, and November-December 2020 and used data from 2665 teachers at public schools (871 individuals participated in all three surveys). Participants reported their fear of infection, fear of transmission of infection to their home or pupils, perceived burnout and stress, and worries about their ability to manage the working conditions. We included information about COVID-19 risk group status, gender, age, organization of teaching (physical presence or remote teaching), and the pupils' grade. We estimated prevalence ratios and took repeated measures into account. RESULTS: Emotional reactions and poor mental health increased significantly with 27-84% from May to November-December 2020. Teachers, who were particularly vulnerable to the adverse consequences of COVID-19, had the highest prevalence of fear of infection and poor mental health. CONCLUSION: Teachers play a crucial role in a society's response to a pandemic. Yet, the dual role of teaching and virus control along with concerns regarding the health consequences of an infection may contribute to the observed increase in emotional reactions to COVID-19 and poor mental health.

Socioeconomic Position and Late-Onset Dementia: A Nationwide Register-Based Study.

OBJECTIVES: Previous research on the association between socioeconomic position (SEP) and dementia has not sufficiently accounted for the complex relationship between education and occupation. We investigated the independent and joint effects of educational attainment and occupation-based SEP on dementia. METHODS: We used register-based information about educational attainment, occupation-based SEP, and dementia from 1,210,720 individuals. Information about cognitive ability at conscription was available for a subsample of men. RESULTS: When mutually adjusted, lower educational attainment and occupation-based SEP were associated with higher dementia risk in a dose-response manner. Higher occupation-based SEP partly mitigated the higher dementia risk associated with lower educational attainment. After adjusting for cognitive ability in a subgroup of men, only unskilled work was associated with higher dementia risk. DISCUSSION: Occupation-based SEP is independently associated with dementia and may mitigate the higher dementia risk associated with short education. Future research should elucidate the mechanisms underlying social inequality in dementia.

Day-to-day pattern of work and leisure time physical behaviours: are low socioeconomic status adults couch potatoes or work warriors?

BACKGROUND: Most studies on day-to-day patterns of physical behaviours (i.e. physical activities and sedentary behaviour) are based on adults with high socioeconomic status (SES) and without differentiating between work and leisure time. Thus, we aimed to characterise the day-to-day leisure time physical behaviours patterns among low SES adults and investigate the influence of work physical behaviours. METHODS: This cross-sectional study included 963 adults from low SES occupations (e.g. manufacturing, cleaning and transportation). The participants wore accelerometers for 1-7 days to measure physical behaviours during work and leisure time, expressed as time-use compositions consisting of time spent sedentary, standing or being active (walking, running, stair climbing, or cycling). Compositional multivariate multilevel models were used to regress daily leisure time-use composition against work time-use compositions. Interaction between weekday and (1) type of day, (i.e., work/non-work) and (2) the work time-use composition were tested. Compositional isotemporal substitution was used to interpret the estimates from the models. RESULTS: Each weekday, workers consistently spent most leisure time being sedentary and most work time standing. Leisure time physical behaviours were associated with type of day (p < 0.005, more sedentary on workdays vs. non-workdays), weekday (p < 0.005, more sedentary on Friday, Saturday and Sunday), standing work (p < 0.005, more sedentary and less standing and active leisure time on Sunday), and active work (p < 0.005, less sedentary and more standing and active leisure time on Sunday). Sedentary leisure time increased by 18 min, while standing and active leisure time decreased by 11 and 7 min, respectively, when 30 min were reallocated to standing at work on Sunday. Conversely, sedentary leisure time decreased by 25 min, and standing and active leisure time increased by 15 and 10 min, respectively, when 30 min were reallocated to active time at work on Sunday. CONCLUSIONS: While low SES adults' leisure time was mostly sedentary, their work time was predominantly standing. Work physical behaviours differently influenced day-to-day leisure time behaviours. Thus, public health initiatives aiming to change leisure time behaviours among low SES adults should consider the influence of work physical behaviours.

COVID-19 Risk Management and Emotional Reactions to COVID-19 Among School Teachers in Denmark: Results From the CLASS Study.

OBJECTIVES: We explored teachers' emotional reactions to the COVID-19 pandemic, and the association between COVID-19 risk management and these emotional reactions. METHODS: We used cross-sectional data from 2665 teachers working at public schools. Participants responded to a questionnaire in May 2020. The analyses were adjusted for sex, age, cohabitation, and region. RESULTS: Knowledge about adequate test behavior and feeling secure regarding colleagues' actions to hinder spread of virus were associated with less frequent emotional reactions. Lack of access to personal protective equipment and exposure to infected pupils, parents or colleagues were associated with more frequent emotional reactions. CONCLUSION: Similar to other groups of frontline employees, teachers experience negative emotional reactions to the COVID-19 pandemic. Gaining knowledge about teachers' worries and fears during pandemics is an important first step enabling leaders and occupational health professionals to address these.

COVID-19 risk management at the workplace, fear of infection and fear of transmission of infection among frontline employees.

OBJECTIVES: We compared COVID-19 risk management, fear of infection and fear of transmission of infection among frontline employees working within eldercare, hospital/rehabilitation, psychiatry, childcare and ambulance service and explored if group differences in fear of infection and transmission could be explained by differences in risk management. We also investigated the association of risk management with fear of infection and fear of transmission of infection among eldercare personnel. METHODS: We used cross-sectional questionnaire data collected by the Danish labour union, FOA . Data were collected 5½ weeks after the first case of COVID-19 was registered in Denmark. Data for the first aim included 2623 participants. Data for the second aim included 1680 participants. All independent variables were mutually adjusted and also adjusted for sex, age, job title and region. RESULTS: Fear of infection (49%) and fear of transmitting infection from work to the private sphere (68%) was most frequent in ambulance service. Fear of transmitting infection during work was most frequent in the eldercare (55%). Not all differences in fear of infection and transmission between the five areas of work were explained by differences in risk management. Among eldercare personnel, self-reported exposure to infection and lack of access to test was most consistently associated with fear of infection and fear of transmission, whereas lack of access to personal protective equipment was solely associated with fear of transmission. CONCLUSION: We have illustrated differences and similarities in COVID-19 risk management within five areas of work and provide new insights into factors associated with eldercare workers' fear of infection and fear of transmission of infection.

Stress diagnoses in midlife and risk of dementia: a register-based follow-up study.

OBJECTIVES: Previous studies indicated that stress diagnoses increase the risk of dementia. However, previous results may be biased by confounding, reverse causation and misclassification. Therefore, the main aim of this study was to investigate the association between clinically diagnosed stress in midlife and later dementia risk, while addressing limitations of previous studies. METHODS: The study population was selected from all individuals in Denmark born 1935-1956. Individuals diagnosed with stress in midlife (aged 37-58 years) were matched (1:5) with individuals without stress diagnoses based on sex and birthdate (N = 103,484). Data were retrieved from national registers. Cox regression models were adjusted for socio-demographic factors and different morbidities. RESULTS: We found a 2.20 (95% CI: 1.93-2.50) times higher rate of dementia among individuals with any stress diagnosis registered in midlife compared with no stress diagnosis. Hazard rate ratios of dementia were 1.73 (95% CI: 1.13-2.65) among individuals with acute stress reactions, 2.37 (95% CI: 2.05-2.74) among individuals with adjustment disorders, and 2.20 (95% CI: 1.73-2.80) among individuals with unspecified stress reactions. Individuals with PTSD and other stress reactions had non-significantly elevated rates of dementia. Adjustment for confounding only slightly attenuated the association, and reverse causation did not appear to bias the results substantially. CONCLUSION: Our results support the hypothesis that severe stress in midlife is an important risk factor for dementia. This finding emphasizes the importance of identifying and treating severe stress in midlife to reduce potential detrimental consequences for brain health in later life.

The effect of occupational physical activity on dementia: Results from the Copenhagen Male Study.

Leisure-time physical activity (LTPA) reduces the risk of dementia, while the effect of occupational physical activity (OPA) on dementia is uncertain. Therefore, the aim of this study was to investigate the effect of OPA on dementia. For comparison, also the association between LTPA and dementia was analyzed. In this longitudinal study, we used self-reported questionnaire data on OPA and LTPA collected in 1970-71 from 4721 male employees, who were 40-59 years old at baseline. Dementia was identified through national registers and participants were followed from they turned 60 years and until 2016. We estimated incidence rate ratios (IRR) and adjusted for age, socioeconomic status, marital status, and psychological stress. In additional analyses, we included health behaviors and blood pressure and mutually adjusted OPA and LTPA. We identified 697 dementia cases during 86 557 person-years. We found an IRR of 1.48 (95% CI: 1.05-2.10) among participants with high OPA compared with participants in sedentary jobs. Participants with high LTPA had a non-significantly lower IRR of dementia compared with participants with a sedentary leisure time. In conclusion, LTPA and OPA are differentially associated with dementia. Therefore, current recommendations regarding the beneficial effect of physical activity on dementia only concern LTPA, and more research on OPA and dementia is needed.

Physical and psychosocial work factors as explanations for social inequalities in self-rated health.

OBJECTIVE: We investigated the contribution of physical and psychosocial work factors to social inequalities in self-rated health (SRH) in a sample of Danish 40 and 50 years old occupationally active women and men. METHODS: In this longitudinal study, the study population consisted of 3338 Danish women and men. Data were collected by postal questionnaires in 2000 (baseline) and 2006 (follow-up). The independent variable, socioeconomic position (SEP), was assessed by the highest achieved educational level at baseline. We conducted gender-stratified parallel multiple mediation analyses. In the mediation analyses, SEP was categorised as SEP I, II, III, VI and V among men. Among women, SEP was dichotomised into SEP I-IV and V. The outcome, SRH, was assessed at baseline and follow-up. A wide range of physical and psychosocial work factors were included as potential mediators. RESULTS: We found a social gradient in SRH across all levels of SEP among men. Among women, we only found a poorer SRH among those with the lowest SEP. Mediation analyses showed that work factors together accounted for 56% of the social inequalities in SRH among men and 44% among women. In both genders, ergonomic exposures and job insecurity seemed to play the major role for social inequalities in SRH. For women only, we also found noise to contribute to the social inequalities in SRH. CONCLUSION: Physical and psychosocial work factors partially explained social inequalities in SRH among both genders. Improvement of the working environment can potentially contribute to the reduction of social inequalities in health.

How to schedule night shift work in order to reduce health and safety risks.

Objectives This discussion paper aims to provide scientifically based recommendations on night shift schedules, including consecutive shifts, shift intervals and duration of shifts, which may reduce health and safety risks. Short-term physiological effects in terms of circadian disruption, inadequate sleep duration and quality, and fatigue were considered as possible links between night shift work and selected health and safety risks, namely, cancer, cardio-metabolic disease, injuries, and pregnancy-related outcomes. Method In early 2020, 15 experienced shift work researchers participated in a workshop where they identified relevant scientific literature within their main research area. Results Knowledge gaps and possible recommendations were discussed based on the current evidence. The consensus was that schedules which reduce circadian disruption may reduce cancer risk, particularly for breast cancer, and schedules that optimize sleep and reduce fatigue may reduce the occurrence of injuries. This is generally achieved with fewer consecutive night shifts, sufficient shift intervals, and shorter night shift duration. Conclusions Based on the limited, existing literature, we recommend that in order to reduce the risk of injuries and possibly breast cancer, night shift schedules have: (i) ≤3 consecutive night shifts; (ii) shift intervals of ≥11 hours; and (iii) ≤9 hours shift duration. In special cases - eg, oil rigs and other isolated workplaces with better possibilities to adapt to daytime sleep - additional or other recommendations may apply. Finally, to reduce risk of miscarriage, pregnant women should not work more than one night shift in a week.

Does Midlife Forgetfulness Influence Positive and Negative Aspects of Social Relations at Work?: Results From the Danish Working Environment Cohort Study.

OBJECTIVES: We investigated whether midlife forgetfulness was prospectively associated with changes in social relations at work (SRW) among occupationally active individuals in Denmark. METHODS: We analyzed data of 2339 men and women participating in the first (1990) and second (1995) survey of the Danish Work Environment Cohort Study, responding to questions on working environment, SRW, and forgetfulness. We used multiple linear regression analysis while adjusting for potential confounders. RESULTS: At baseline (1990), 517 (22.1%) study participants were categorized as forgetful. Forgetfulness was prospectively associated with a decline in one of the investigated items reflecting a negative aspect of SRW (experiencing teasing, regression coefficient = 0.07, 95% CI: 0.03 to 0.11), while no association was observed with positive aspects of SRW. CONCLUSIONS: Our findings did not support the hypothesis that memory problems such as midlife forgetfulness negatively affect SRW.

The Effect of Psychosocial Work Factors on Headache: Results From the PRISME Cohort Study.

OBJECTIVE: To investigate the cross-sectional and longitudinal association between psychosocial work factors, assessed as work-unit averages, and headache. For comparison, we also applied individual exposure measures. METHODS: We used questionnaire-data on headache and psychosocial work factors (PWF). In total, 2247 employees were included in the cross-sectional analyses and 553 in the longitudinal analyses using work-unit averages. The corresponding numbers for the analyses using individual exposure measures were 4261 and 942 employees. RESULTS: Low skill discretion and low decision authority were most consistently associated with higher odds of headache across all analyses. Role conflicts, bullying, and effort-reward imbalance were associated with headache in some analyses. All PWF were associated with headache in cross-sectional analyses with individual exposure measures. CONCLUSION: This study partly supports the hypothesis of an effect of PWF, as a source of psychological stress, on the risk of headache.

Mid- to late-life migraine diagnoses and risk of dementia: a national register-based follow-up study.

BACKGROUND: Previous studies found an association between migraine and dementia, which are two leading causes of disability. However, these studies did not differentiate between migraine types and did not investigate all prevalent dementia subtypes. The main objective of this national register-based study was to investigate whether migraine was a risk factor for dementia. Additionally, we explored potential differences in dementia risk for migraine with and without aura. METHODS: We obtained data on birth cohorts born between 1935 and 1956 (n = 1,657,890) from Danish national registers. Individuals registered with migraine before age 59 (n = 18,135) were matched (1:5) on sex and birthdate with individuals without migraine (n = 1,378,346). Migraine was defined by International Classification of Diseases (ICD) diagnoses and dementia was defined by ICD diagnoses and anti-dementia medication. After matching, 62,578 individuals were eligible for analysis. For the statistical analyses, we used Cox regression models and adjusted for socio-demographic factors and several psychiatric and somatic morbidities. RESULTS: During a median follow-up time of 6.9 (IQR: 3.6-11.2) years, 207 individuals with migraine developed dementia. Compared with individuals without migraine, we found a 50% higher rate of dementia among individuals with migraine (HR = 1.50; 95% CI: 1.28-1.76). Individuals without aura had a 19% higher rate of dementia (HR = 1.19; 95% CI: 0.84-1.70), and individuals with aura had a two times higher rate of dementia (HR = 2.11; 95% CI: 1.48-3.00). CONCLUSIONS: Our findings support the hypothesis that migraine is a midlife risk factor for dementia in later life. The higher rate of dementia in individuals with a hospital-based diagnosis of migraine with aura emphasizes the need for studies on pathological mechanisms and potential preventative measures. Furthermore, given that only hospital-based migraine diagnoses were included in this study, future research should also investigate migraine cases derived from the primary healthcare system to include less severe migraine cases.

Shift work and incidence of dementia: A Danish Nurse Cohort study.

INTRODUCTION: A few studies suggest that working night and rotating shifts increase the risk of dementia. We examined the association between shift work and the incidence of dementia in a cohort of female Danish nurses. METHODS: We linked Danish Nurse Cohort participants, who reported work schedules (day, evening, night, rotating shifts) in 1993 and/or 1999 and their duration in 2009, to Danish registers to obtain information on dementia hospitalizations and prescription medication until November 2018. RESULTS: Among 6048 nurses who reported work schedules in 1993 and 1999, nurses working night shifts ≥6 years had higher dementia incidence (hazard ratio: 2.43, 95% confidence interval: 1.39 to 4.23) than those working day shifts ≥6 years. Among 8059 nurses who reported shift work duration, nurses working night shifts ≥6 years had higher dementia incidence than those working night shifts <1 year (1.47, 1.06 to 2.06). DISCUSSION: Persistent night shift work may increase the risk of dementia.