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Hoorn study

Objectives

Diabetes is defined by the presence of elevated blood glucose levels and is usually accompanied by an unfavourable cardiovascular disease risk profile. In the Netherlands, approximately 10% of the population aged 50–75 years old has type 2 diabetes mellitus. Partly due to the aging population and partly due to changes in lifestyle and the resulting epidemic of obesity, the percentage of people with diabetes is growing rapidly and is estimated to increase to one-third of the adult population in 2010. One of EMGO’s diabetes research programmes is aimed at identifying risk factors for type 2 diabetes and its complications and at developing strategies for prevention. In 1989, the Hoorn Study was initiated to study the prevalence and determinants of type 2 diabetes in the general population in the Netherlands. The Hoorn Study cohort has been monitored ever since and has been extended to include additional study populations. The number of ongoing research projects within the Hoorn Study grew over time, and so, in November 2005, a new and larger Diabetes Research Centre opened near Hoorn’s local hospital. The new centre is equipped with a vascular laboratory, an ophthalmologic examination unit, storage facilities, and test equipment, and well-trained research assistants have been appointed to guarantee the quality of the research.

The initial objective of the Hoorn Study was to determine the prevalence of type 2 diabetes and associated risk factors in a population-based cohort study. In 1989, a random sample was taken from the city of Hoorn’s municipal register. Of the 3553 men and women aged 50–75 years old who were invited, 2540 (71.5%) agreed to participate. Of those, researchers excluded 56 non-Caucasian subjects, resulting in the initial Hoorn Study cohort of 2,484 subjects. All participants, except those who were on glucose-lowering medication, underwent an oral glucose tolerance test, which consisted of drinking a solution of 75 g glucose in 300 ml water after an overnight fast. They underwent a physical examination and completed questionnaires on their health status and lifestyle. The objectives were later extended to study risk factors for diabetes and cardiovascular disease and other diabetes complications in a prospective follow-up of the original cohort. The study population has since been increased to include new samples of diabetic patients and patients with impaired glucose tolerance. Repeated medical examinations and follow-ups of morbidity and mortality in a well-defined population make it possible to study new risk factors and effective methods for the prevention and treatment of chronic disease. The many facets of diabetes are being studied in a multidisciplinary approach, involving collaboration with specialists from various fields of research.

Collaborations

National collaborations

Universities of Leiden, Maastricht, Rotterdam and the University of Amsterdam

The National Institute for Public health and the Environment (RIVM), the Netherlands Institute for health Services (NIVEL) and the Dutch Institute for Healthcare Improvement (CBO).

International collaborations

Partnership in socio-economic studies in diabetes and obese people: Novo Nordisk Copenhagen, Denmark and Lund University, Sweden
Coordination of a multicentre study on the role of insulin resistance in the pathophysiology of diabetes and cardiovascular disease: CNR Institute of Clinical Physiology, University of Pisa,  Italy
Epidemiological study using combined data from 11 European population studies: The DECODE Study Group (Helsinki Finland) and Steno Diabetes Centre, Gentofte, Denmark

Study of the effects of SMBG in type 2 diabetes patients not using insulin: Life-scan, USA European Best Information through Regional Outcomes in Diabetes (EUBIROD) Twenty partners over different European countries

Results

More than 150 international publications and more than 20 dissertations are already published since 1989. There are too many results to sum them up here. We have chosen some fine examples. At the start we showed that approximately 8% of all participants had diabetes, 4% of whom were previously undiagnosed. Extensive measurements were performed in a stratified sample of the total study population. In this stratified sample vascular- and autonomic-function tests and tests for the presence of atherosclerosis, neuropathy, nephropathy, and retinopathy were performed. As expected, the risk of complications was highest in the known diabetic patients. Also was found that patients with newly diagnosed diabetes, and even patients with impaired glucose tolerance, had a worse cardiovascular risk profile and also performed worse on a number of the function tests than people with normal glucose tolerance. In addition, the follow-up study of patients with impaired glucose tolerance showed that over 30% progressed to diabetes within five years. In collaboration with the general practitioners and the local hospital, researchers are monitoring morbidity and mortality in the Hoorn Study cohort. The population register of the city of Hoorn provides information on the vital status of the participants who gave informed consent. Causes of death and information about morbidity are extracted from the medical records in the general practices and the local hospital. A specially developed computer programme is being used to classify morbidity and mortality according to the International Classification of Diseases, Injuries, and Causes of Death. During ten years of follow-up, participants with known diabetes had a four-to-five times higher risk for all-cause and cardiovascular mortality, compared to participants with normal glucose levels. The combined presence of diabetes and a history of cardiovascular disease were associated with an even higher, six-fold risk for a cardiovascular event in both men and women. These differences also reflected associations between the metabolic syndrome and cardiovascular disease. In the vascular function study part, we found that increased arterial stiffness was already apparent in participants with impaired glucose metabolism, thus preceding diabetes. The contribution of different regional fat depots or lean tissue to arterial stiffness was studied and larger trunk fat mass was associated with higher peripheral arterial stiffness, but not with central arterial stiffness. Also was shown that fat distribution was associated with differences in lipoprotein lipase activity and hepatic lipase activity, which are key enzymes in lipid metabolism. At present, a new follow-up examination is being carried out in the surviving participants of the Hoorn Study. This time, focus is on cognitive function in relation to insulin resistance, hyperglycaemia, and level of atherosclerosis. 

In 2006, the New Hoorn Study began, also a population-based cohort study, this time in 2700 men and women, aged 40–65. So, this study cohort is younger than the original Hoorn Study. The focus of this study will be on determinants of beta-cell function and the change of the prevalence of impaired glucose regulation and diabetes over time. As possible determinants of beta-cell function, initial studies will investigate the contributions of lifestyle, including stress.

Contact information

Responsible for the Hoorn Study are:

Prof. Dr. Ir. J.M. Dekker: +31204448173; mail: jm.dekker@vumc.nl
Prof. Dr. G. Nijpels: +31204449659; mail: g.nijpels@vumc.nl