Baseline data collection of the HELIUS database took place from January 2011 until November 2015. Approximately 25,000 participants were included, including an equal distribution of participants of Turkish, Moroccan, African Surinamese, South-Asian Surinamese, Ghanaian, and Dutch origin. Ethnic origin is determined from a person’s country of birth and that of his/her parents. Subjects were randomly sampled, stratified by ethnic origin, from those aged 18–70 years listed in the Amsterdam Municipal Register, and invited to participate in HELIUS.
When individuals agreed to participate, they filled in an extensive questionnaire. Participants unable to fill in the questionnaire were offered assistance from a trained (ethnically matched) interviewer. The questionnaire addresses the presence (or symptoms) of cardiovascular diseases, mental health disorders, and infectious diseases as well as determinants or risk factors for these diseases and disorders. Examples of risk factors that were addressed: demographic variables (marital status, household composition), migration history, educational and occupational level, religion, cultural distance (acculturation), perceived discrimination, lifestyle factors (smoking, alcohol intake, cannabis use, physical activity, travel behavior, sexual behavior), health care use, family history of diseases, stressful life events. For a complete overview of the design and variables see Stronks et al. (BMC Public Health 2013) and Snijder et al (BMJ Open 2017).
The baseline physical examination took place at a local research site, and the following measurements were performed: anthropometry (weight, height, circumferences of waist, hip, thigh, arm, calf), handgrip strength, body fat percentage (bio-electrical impedance), blood pressure, ankle-arm index, electrocardiogram, arterial stiffness, heart function (non-invasive haemodynamics such as stroke volume and cardiac output). Medication use was recorded. Fasting blood samples were drawn for determination of haemoglobin, HbA1c, glucose, lipid profile, and creatinine levels. Microalbumin and creatinine were determined from a morning urine sample. Female participants were asked to take a self-administered vaginal swab. Urine and blood samples were stored in biobank for future analyses.
In different subsamples, additional data/samples were collected: dietary intake (n≈5,000), endothelial glycocalyx (n≈5,000), faeces samples (n≈6,000), health literacy test (n≈10,000), nasal and throat swabs (n≈7,000).
Expansion of infrastructure
Currently (2019-2020), participants are re-invited for follow-up measurements to study changes in risk factors and the incidence of diseases over time. In addition, participants’ data are and will be linked to registry data for routinely collected data on health outcomes and health care (e.g. mortality, hospital admission) at the individual level (through a double anonymized linking procedure). Potentially useful databases/registries to be linked to the HELIUS data collection include local GP registries, hospital discharge registries, pharmacy data (prescriptions), and health care insurance registries (health care use).
Possibilities for research
The unique ethnic differentiation in the HELIUS infrastructure can be utilized for scientific research in two ways. First, the HELIUS infrastructure can be used to investigate which factors possibly explain ethnic inequalities in health, such as socio-economic factors, culture, migration history, ethnic identity, discrimination, and genetic factors. Second, the HELIUS infrastructure provides an excellent opportunity to study the etiology of medical conditions, because ethnic variation amplifies variations in underlying risk factors, facilitating the study of those risk factors. HELIUS will thus contribute to the evidence base for the prevention of diseases and promotion of population health in general, and the reduction of ethnic inequalities in health in particular.