86 Chapter 5 5.3 METHODS 5.3.1 Participants and study design This study is based on data acquired within the Age Gene/Environment Susceptibility (AGES)-Reykjavik study, a population-based study.14 The study was approved by the Icelandic National Bioethics Committee, VSN:00-063, and the institutional review board responsible for the National Institute on Aging (NIA) research. All participants signed informed consent. Participants of the AGES-Reykjavik study (n = 4614) were born between 1907 and 1935 and underwent brain MRI scans between 2002 and 2006.14 Diagnosis of dementia at baseline was assessed in a three-step process, as described previously.15 Briefly, all participants underwent the Mini-Mental State Examination and the Digit Symbol Substitution Test. Based on positive results of the tests, participants were administered a second battery of diagnostic tests and possibly a third step, which included neurological tests and a proxy interview.15 Possible outcomes were dementia, mild cognitive impairment, or normal cognition. Age, sex, education level, and smoking status were assessed via questionnaires at baseline. Education levels are primary school, secondary school, college, and university. The highest level of education completed was entered. Smoking status was categorized as non-smoker, former smoker, and current smoker. Participants who never smoked were classified as non-smokers, participants who smoked regularly and at least 100 cigarettes or 20 cigars in a lifetime were classified as former smokers, and participants who currently smoke were classified as current smokers. Body mass index (BMI) was calculated using height (cm) and weight (kg). Hypertension was defined as self-reported or use of antihypertensive medication or measured systolic blood pressure > 140 mm Hg and/or diastolic blood pressure > 90 mm Hg. Systolic and diastolic blood pressure were measured with a standard mercury sphygmomanometer, and the mean of two measurements was calculated. Diabetes mellitus was defined as self-reported history of diabetes, use of anti-diabetic medication, or fasting blood glucose level > 7.0 mmol/L. Coronary artery disease was defined as a self-report of angina plus the use of nitrates or evidence of myocardial infarction (on ECG). Brain infarcts were defined as the presence of subcortical, cerebellar, or cortical brain infarcts. Results from individual examinations in the study, including MRI findings, were sent to the general practitioner of the study participant in a doctor´s report. The general practitioner then acted according to clinical guidelines. In case of major incidental
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