Part 1 | Vascular risk factors for depression and apathy 65 4 Physical activity was measured using a short version of the Voorrips questionnaire counting household activities and sports. The use of tertiles to categorize a low, a medium or a high level of physical activity is validated for an elderly population living at home 37. Acknowledging that in epidemiological research, self-reported CVRF and CVD are proxies for cerebrovascular lesions, we established a ranking in 4 levels on how closely they represent cerebrovascular damage: • The reference group had none or 1 diagnosed cerebrovascular risk factor and no cardiac disease or cerebrovascular disease (level 0 in our ranking) . • ’ ≥2 vascular risk factors’ consisted of ≥2 CVRF (hypertension, diabetesmellitus, hyper- cholesterolemia, smoking, severe obesitas, low physical activity) without evidence of cardiovascular or cerebrovascular disease. This category was ranked level 1. The use of this cut-off was based on statistical arguments: (1) this cut-off would result in large enough groups to study interactions; (2) a higher cut-off did not result in a larger association with depression (data not shown). • ‘Cardiac disease’ was defined as myocardial infarction, angina pectoris, heart failure or atrial fibrillation) (level 2). • Participants that had experienced a transient ischemic attack (TIA) or cerebrovascular accident (CVA) were classified as ’ stroke’ (level 3). • When we use the term ‘ vascular disease’ we refer to all 3 levels: ’ ≥2 vascular risk factors’; ‘cardiac disease’ or ‘stroke’. Possible confounders In the knowledge that a history of depression, somatic comorbidity and sociodemographic variables predict a large portion of the variance of elderly major and subsyndromal depression in the general population 38 39, the following possible confounders were assessed: age, educational level, marital status, disability, chronic diseases and a history of major depression. Educational level was based on the highest level of education completed by participants and coded low/medium/high. Marital status was asked for and dichotomized into ‘currently living together with partner’ or ‘currently living alone’. Disability was established by asking if participants walked freely or used a stick or wheelchair outside. This variable was dichotomized into ‘none’ or ‘some disability’. The self-reported presence of chronic lung disease, chronic kidney disease, chronic liver disease, Morbus Crohn or colitis ulcerosa, cancer and rheumatic arthritis or arthrosis were added to compute a composite score for somatic comorbidity. Three levels of somatic comorbidity were used: none; one comorbid disease; two or more comorbid diseases. This definition yielded (i) large enough groups and (ii) the highest univariate associations with depression. Furthermore, a self-reported history of treated lifetime depression (yes/ no) was included as a covariate in the analysis. Statistical methods Differences between the depressed and the non-depressed control group were tested with Pearson’s Chi-square for categorical and dichotomous variables and Student’s T-test
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