Details of the non-participants are described elsewhere [17]. Blood samples were collected from 62,664 of the study population whenever they attended, and stored at HUNT 2 Biobank [16]. In 2002, all surviving participants (n = 61,426) were asked for permission to use the blood samples in genetic analyses. Over 98% (n = 60,241) accepted this [16]. Analyses on the Val158Met polymorphism have been carried out on 5,531 participants, of whom 4513 (82%) were selected completely at random. The first 1018 (18%) subjects were randomly selected among an older group who did not have self-reported diabetes mellitus [18]. This group was generated in connection with a planned genetic study on diabetes that needed age-matched controls to a diabetic population. As a consequence, the prevalence of self-reported diabetes mellitus was somewhat lower among individuals with known genotype than among those without COMT data available (1.3% versus 3.2%, p < 0.001).
