114 Chapter 6 in a random sample from the general population in Iceland. Participants were born between 1907 and 1935 and were living in Reykjavik in 1967. Remaining participants of the cohort were randomly selected for a follow-up and underwent a baseline brain MRI scan between 2002 and 2006. Baseline diagnosis of dementia was assessed in a 3-step process, as described previously.9 In short, participants underwent the Mini-Mental State Examination and the Digit Symbol Substitution Test. Participants were administered a second battery of diagnostic tests based on positive results in the previous tests and possibly a third stage, which included neurologic tests and a proxy interview.9 Based on these tests, participants were considered to have normal cognition, mild cognitive impairment, or dementia at baseline. Dementia diagnosis based on the Diagnostic and Statistical Manual, Fourth Edition, guidelines was made in a consensus meeting with a geriatrician, neurologist, neuropsychologist, and neuroradiologist. Education level and smoking status were collected using questionnaires. The highest completed education level (primary school, secondary school, college, and university) was entered. Participants who never smoked were categorized as non-smokers, participants who smoked regularly and at least 100 cigarettes or 20 cigars in a lifetime were categorized as former smokers, and participants who currently smoke were categorized as current smokers. Height (in centimeters) and weight (in kilograms) were measured and used to calculate body mass index. Hypertension was based on self-report, use of antihypertensive medication, or based on the measurements of systolic blood pressure >140 mm Hg and/or diastolic blood pressure >90 mm Hg. A standard mercury sphygmomanometer was used to measure systolic and diastolic blood pressure; the mean of 2 measurements was calculated. Diabetes mellitus was based on self-report of diabetes, use of antidiabetic medication, or fasting blood glucose level >7.0 mmol/L. Coronary artery disease was based on self-report plus the use of nitrates or evidence of a myocardial infarction on electrocardiogram. Participants were followed from the date of the baseline MRI scan until diagnosis of dementia, loss to follow-up, or end of follow-up. Loss to follow-up means that the participants died or could not be contacted. Tracking for dementia diagnosis was done through vital statistics and hospital records and by the nursing home and home-based resident assessment instrument. The dementia follow-up of the AGES Reykjavik Study was concluded in 2015 (end of follow-up). The inclusion and exclusion of participants from the AGES Reykjavik Study for the current study is illustrated in Figure 6.1. For example, participants who were demented at baseline were excluded.
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