Cindy Boer

148 | Chapter 3.2 Supplementary Materials Study population and clinical data The Rotterdam study (RS) is a large prospective population-based cohort study ongoing since 1990 to study determinants of chronic disabling diseases in the elderly[1]. All co- hort participants live in the Ommoord district of the city of Rotterdam, the Netherlands. Residents 55 years and older were first recruited in 1990. In 2000, a second cohort, RS-II, was started with individuals who had become 55 years of age or moved into the study district since the start of the study. Follow-up data were collected as follow-up visits every ~4-5 years. Details of the design and rationale of the Rotterdam Study has been published elsewhere1. Participant measurements at baseline and follow-up were obtained during visits to the research center for physical examinations, computerized pharmacy records, and from home interviews. Our study included participants of RS-I and RS-II for whom radiographs of knee and hip joints at baseline and follow-up visit were present obtained and scored. Additional information collected included: sex, age at baseline visit, body mass index (BMI, kg-1m2), physical activity (metabolic equiva- lent of task/hours per week), smoking (never, former and current smoker), education level (UNESCO education classification), Diabetes mellitus, hypertension, femoral neck bone mineral density (FN-BMD), HDL/total cholesterol ratio and Stanford Health As- sessment Questionnaire. The Medical Ethics Committee of the Erasmus MC, University Medical Center, has approved of the Rotterdam Study (MEC 02.1015). All participants provided written consent prior to participation in the Rotterdam Study. Computerized pharmacy data of VKA and antiplatelet use For 98% of the participants of the RS-I and RS-II, medication usage was available through fully computerized pharmacies within the Ommoord district. All data on dis- pensed drugs were available in computerized form on a daily basis. Information was available on the date of prescribing, the total amount of drug units for each prescription, the prescribed daily number of units, the product name and the therapeutic chemical code1. For each participant, we extracted the usage of VKAs(acenocoumarol) and anti- platelet agents (acetylsalicylic acid, carbasalate calcium and Clopidogrel), for the period between baseline and follow-up. We extracted information on the prescription of the VKA acenocoumarol. Warfarin is not prescribed, as it is not registered for use as a drug in the Netherlands. All patients taking VKAs in this study attended an anticoagulation clinic, which is standard practice in the Netherlands [2].