DAD - Danish Working Hour Database

Comprehensive data on working hours

The Danish Working Hour Database (DAD) was established with the purpose to provide a detailed data source to describe and investigate possible associations between the working environment including working hours, well-being and health and labor market-related outcomes such as labor market attachment and retention. 

DAD is based on administrative data and includes daily starting and ending time of working hours for all employees in the five administrative Danish Regions since 2007. As of today, the database contains information from 343,620 individuals. DAD consists of three datasets, which are described in more detail below:

1. DAD – working hour includes information from payroll registers (n=343,620) 
2. DAD – lifestyle includes questionnaire data (n=37,077) 
3. 1001 nights cohort includes questionnaires, logbooks, continuous technical measures and biological samples (n=1075) 

Purpose of DAD

In 2012, the Danish Working Hour Database (DAD) was established as a research data structure for scientific investigations of health and safety risks associated with shift work, which can be used as a human model for circadian disruption. Up until then, research in shift work was limited by lack of large-scale epidemiological cohorts with accurate and detailed assessment of working hours and diseases. The establishment of DAD provided the possibility to assess important working hour characteristics such as type of shifts, e.g. day, evening, and night shifts, as well as other relevant features related to the scheduling of shifts, e.g. number of consecutive night shifts and duration of shifts. The capturing of such measures in future epidemiological studies is crucial for the design of healthy working hours in general and shift work schedules in particular.

The foundation for future research and societal change

Over the years it has become evident that the unique and highly granulated information on working hours around the clock at an individual level has great potential when it comes to research in areas as divergent as biomedicine, public health and economics, technical and computational sciences, e.g. for studies on:

• Biomedical mechanisms in development, treatment and prevention of disease related to circadian disruption, using night work as a model in humans; 
• Design of healthy and safe 24-7 working hour schedules and lighting conditions for the benefit of employees and employers across industries;
• Development of models using machine learning

DAD has been used to study multiple outcomes in relation to shift work including accidents, long and short-term sickness absence, and pregnancy-related outcomes. The results of these studies have already been used for making recommendations on how to organize work schedules to reduce risk related to health, safety and pregnancy. These recommendations have, in turn, been taken up and put to practice by authorities, employer and employee organizations, work environment professionals, workplaces and employees.

DAD – working hour 

With “DAD – working hour” the main aim is to study health and safety effects of working hours, particularly shift work, which can be used as human model for circadian disruption. Data contains day-to-day information on working hours from 2007 and onwards for all employees in the Danish Regions i.e. covering all the Danish public hospitals (343,620 employees). Data may be linked to health outcomes at individual level through Danish national health registers. This provides the possibility to study associations between shift work or circadian disruption and outcomes such as cardio-metabolic disease, diabetes, cancer, mental disorders, injuries and pregnancy-related diseases.

DAD – lifestyle 

The dataset includes self-reported information on lifestyle (smoking, alcohol consumption, height, weight (at age 20 and current), previous night work and diurnal preference. A brief questionnaire was sent to all employees from three of the five Danish regions. Hereof, 37,077 employees (56.2%) responded.

1001 nights cohort

The dataset includes information and a biobank from 1075 employees at public Danish hospitals with and without night shift work, who were enrolled in a comprehensive data collection in 2022-2024. For all participants this included a background questionnaire, blood sample, blood pressure and anthropometric measures from one day, together with sleep actigraphy and a sleep and activity diary for 14 consecutive days. In addition, saliva samples were collected every 4 hour on one selected day. Light exposure, physical activity, skin temperature and blood glucose were measured continuously for seven days using wearables in subsamples. Data can be used for short-term effect studies of circadian disruption and biomarkers of cardiometabolic disease, diabetes and cancer.

Data access policy

Use of data for research within in the purpose of the aim is most welcome. All data are accessible at Statistics Denmark through collaboration with a Danish research institution e.g. the National Research Centre for the Working Environment. 

Data from DAD – working hour and DAD – lifestyle may be accessed for research purposes through application to the DAD steering committee.

General provisions regarding the Danish Working Hour Database 

Data from 1001 nights cohort may be accessed for research purposes through application to the custodian Anne Helene Garde (ahg@nfa.dk).

Linkage to national register

The datasets may be linked at an individual level. Information on a number of outcomes including health (all diagnoses including cardiometabolic disease, cancer and mental health) and labor market affiliation (including sickness absence, social benefits and pension) may be obtained through linkage to national registers at an individual level. Examples of such registers are given below:

• Danish National Patient Registry with data on clinical diagnoses for inpatients 1977-2020 and outpatients 1994-2020 according to International Classification of Diseases 8th revision (ICD-8) 1977-1993 and to International Classification of Diseases 10th revision (ICD-10) 1994-2020.
• Danish Register of Causes of Death with date and classification of causes of death by ICD-10 codes, 1970-2020.
• Statistics Denmark's education registry with information on all educations attained 1970-2020.
• Danish National Prescription Registry with information on all fillings of prescriptions coded according to Anatomical Therapeutic Chemical (ATC) classification, 1995-2020.
• Danish Personal Registration System with individual level data on first-degree relatives, vital status and date of disappearance, emigration and death 1968-2020.
• AMR-UN with information on labor market affiliations from 2008 and onwards of all Danish citizens with less than 4% imputed paid hours of work for employees in 2013. 
• Danish Cancer Registry with records on all cancers diagnosed in Denmark since 1943.
• Danish Medical Birth Registry with information related to all births in Denmark since 1973.

DAD Steering Committee

The DAD Steering Committee consists of:

• Professor Anne Helene Garde, The National Research Centre for the Working Environment (NFA), ahg@nfa.dk (custodian), 
• Senior researcher Johnni Hansen, The Danish Cancer Society Research Center, Denmark, johnni@cancer.dk, 
• Professor, overlæge Henrik Kolstad, Department of Occupational Medicine, Danish Ramazzini Centre, Aarhus University Hospital, Aarhus, Denmark, henkol@rm.dk, 
• Professor Emerita Åse Marie Hansen, Department of Public Health, University of Copenhagen, Denmark, asemarie.hansen@sund.ku.dk.

Advisory board

There is an advisory board with representatives from each of the Danish Regions.

Contact

For more information, please contact Professor Anne Helene Garde, The National Research Centre for the Working Environment (NFA), ahg@nfa.dk