We identified all inhabitants in Central Denmark Region between 18-75 years on December 31 2018 in the Danish Civil Register (n=942,572).  From this population all persons with diabetes were identified by the use of national Danish registers. Persons with diabetes were identified based om hospital diagnoses (ICD-10 codes DE10-DE14) from the Danish National Patient Register, redeemed glucose-lowering medications were retrieved from the Danish National Prescription Register (ATC-code A10, except Saxenda), diabetes-specific podiatrist services from the Danish National Health Service Register, and laboratory results for HbA1c (≥ 48 mmol/mol) from the Clinical Laboratory Information System in Central Denmark Region, LABKA II (NPU27300 and NPU03835) (See Register data).

In total, 44,648 persons with diabetes were identified. From the remaining population in the Central Denmark Region (n=895,065), a group without diabetes (n=46,187) matching the population with diabetes on gender, age and municipality were drawn by use of a simple random sample i.e. the matched group without diabetes is not matched directly with an individual with diabetes.

We distributed an electronic questionnaire to the eligible members of the cohort on November 18 2020 and the survey data collection ended on February 7 2021.In total, 51,854 persons responded to the questionnaire (57.1% of the invited). Among persons with type 1 diabetes 2,832 (55.9%) responded to the survey, among persons with type 2 diabetes 21,140 (53.2%), and of those without diabetes 27,882 (60.4%) responded to the survey.

The following information was collected through questionnaire between Nov 18 2020 and Feb 7 2021:

• Anthropometrics
• Well-being
• Symptoms and diseases
• Sleeping problems
• Dyspnoea
• Sexual dysfunction
• Taste and smell
• Dental health
• Fertility
• Diabetic status
• Diabetes-specific problems and motivation

The following register data are available in the HICD:

Danish National Patinet Register

Danish National Health Service Registry

Danish National Prescription Register Statistic

Clinical Laboratory Information System (LABKA), The Central Denmark Region

Register of Laboratory Results for Research

Cause of Death Register

Statistics Denmark

Most of the registers data are available more than 20 years before inclusion in the cohort.

Register data will be updated every second year until the end of 2030.

The study population will be followed up on questionnaires and registers during follow up until the end of 2030. We plan to send out questionnaire twice during this period. Follow-up questionnaires will be send out to the first invited population even if the first questionnaire was not completed. Register data will be updated every second year. For those who develop diabetes during the follow-up period, we will register the date of diagnosis according to the same algorithm used by the initiation of the HICD cohort.

In 2022, a second questionnaire was distributed to 13,000 individuals who had confirmed that they would like to participate in future studies from SDCA. More than 8,000 individuals answered this questionnaire. This population is now a source for recruiting participants to clinical studies based on SDCA.

In February 2024 a new questionnaire will be distributed to all individuals who were invited in 2020 and to all who have been diagnosed with diabetes since 2020 and to a matching control group. In total more than 130,000 will receive the questionnaire.

Cohort profile: Health in Central Denmark (HICD) cohort - a register-based questionnaire survey on diabetes and related complications in the Central Denmark Region
Characteristics of the cohort is published in the cohort profile paper: https://pubmed.ncbi.nlm.nih.gov/35798528/

Perception of Artificial Intelligence in Healthcare Among People with and Without Diabetes
Furthermore, a study examining Artificial Intelligence among individuals with and without diabetes has been published https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4181697 

Oral health in diabetes
A cross-sectional study with more than 40.000 participants found that a higher proportion of people with type 2 diabetes reported poor oral health compared to those without diabetes. Moreover, educational attainment modified the effect of diabetes on oral health, showing that the risk of reporting poor oral health increased with lower educational attainment https://pubmed.ncbi.nlm.nih.gov/37500424/

Inequalities in healthcare utilisation among adults with type 2 diabetes
A new study sheds light on the healthcare attendance of adults with type 2 diabetes in the Central Denmark Region. The cross-sectional register-based study examined the prevalence of attending the ophthalmologist, podiatrist and dentist/dental hygienist among over 40.000 Danes with type 2 diabetes and found significant sociodemographic inequality in healthcare utilisation among people with type 2 diabetes, especially for dental attendance. The full article is available here https://pubmed.ncbi.nlm.nih.gov/37890705/

The HICD is managed by a steering committee at SDCA consisting of members from both epidemiological and clinical diabetes research. The steering committee strongly encourage interested researchers across discipline to use this research resource. SDCA will provide applicants with detailed information on the available data and the application procedure. To get access to data please apply to the steering committee: auh.helbredimidt@rm.dk

Research on HICD-data based on questionnaires and register data require no ethical approval of projects. All data analyses are to be performed on SDCA's remote access to Statistics Denmark's server.  Clinical studies which want to recruit participants from HICD likewise apply to the steering committee: auh.helbredimidt@rm.dk

A senior researcher affiliated with SDCA will be the contact person to a potential research project and 'and responsible for the performing of analyses at Statistics Denmark's server. The application process includes project approval by the steering committee, preparation of dataset, data extraction and access to Statistics Denmark. Normally this process takes four to six months, but will be dependent on the human resources at SDCA.