Is income area level associated with blood pressure in adults regardless of individual-level characteristics? A multilevel approach Doroteia A. H ¨ ofelmann a,n , Jose ´ Leopoldo F. Antunes b , Diego A. Santos Silva c , Marco A. Peres a a Post-Graduate Program in Public Health, Federal University of Santa Catarina, Floriano ´polis, Brazil b Department of Epidemiology, School of Public Health, University of S ~ ao Paulo, S ~ ao Paulo, Brazil c Post-Graduate Program in Physical Education, Federal University of Santa Catarina, Floriano ´polis, Brazil article info Article history: Received 13 October 2011 Received in revised form 5 March 2012 Accepted 9 June 2012 Available online 26 June 2012 Keywords: Blood pressure Cross-sectional studies Income Multilevel analysis Residence characteristics abstract This population-based health survey was carried out in Florianopolis, Brazil, to assess the association between adult systolic blood pressure (SBP) and contextual income level, after controlling for potential individual-level confounders. A statistically significant negative association between SBP levels and contextual income was identified after adjusting for individual-level characteristics. SBP levels in the highest and in the intermediate tertiles of contextual income were 5.78 and 2.82 mmHg lower, respectively, than that observed in the bottom tertile. The findings suggest an association between income area level and blood pressure, regardless of well-known individual-level hypertension risk factors. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Individual socio-demographic characteristics, such as income, schooling, and race, along with obesity, physical activity, and smoking, are well-known factors associated with an increase in blood pressure. Evidence strongly suggests that the neighborhood in which people live influences their health status, and recent research points out that the contextual aspect may affect blood pressure (Merlo et al., 2004; Chaix et al., 2008). Socioeconomic neighborhood conditions, mainly when measured by income, can be highly variable with time, and there is evidence that blood pressure is sensitive to those fluctuations (Matthews et al., 2002). Blood pressure is also considered a physiological consequence of differential exposure to social, physical, and psychological stressors (Spruill, 2010). There is limited information linking contextual socioeconomic characteristics and blood pressure after controlling for individual blood pressure risk factors in middle- and low-income countries. We are not aware of any study focusing on this issue in Latin American countries, where income inequality ranks among the highest in the world (Lopez and Perry, 2008). Profound socioeconomic inequalities are observed in Brazil. Despite advances in recent decades, the country has one of the highest Gini indexes (0.53) in the world (United Nations, 2011). Furthermore, studies across the country have shown that the prevalence of hypertension among adults ranges from 21.9 to 44.4. The differences can be attributed to different methods of measurement and socioeconomic backgrounds of the studied population (Passos et al., 2006). The aim of this study was to assess the association of adult systolic blood pressure (SBP) and high levels of blood pressure (HBP) with contextual income level in 63 census tracts in a Southern Brazilian city. 2. Methods 2.1. Sampling procedures A population-based cross-sectional study called EpiFloripa was carried out in Floriano ´ polis, the capital of the southern Brazilian state of Santa Catarina, from September 2009 to January 2010. The city has a population of nearly 400,000. The sample size was calculated considering the following parameters: prevalence (50%), 95% confidence level, a sample error of 3.5 percentage points, a design effect of 2 because of the cluster sample design, and the addition of 10% to compensate for refusals. An over- sample of 15% was included to allow controlling for confounders in the study of associations (n ¼ 2016 adults). We selected 60 of the 420 urban census tracts of the city, ranked according to average monthly income of the head of the family (IBGE—Instituto Brasileiro de Geografia e Estatı ´stica, 2001). We used a systematic sample, with six census tracts in each income decile. All selected census tracts were visited by the fieldwork team, Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/healthplace Health & Place 1353-8292/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.healthplace.2012.06.010 n Corresponding author. Tel.: þ55 51 48 9941 4312. E-mail address: doroaph@yahoo.com.br (D.A. H ¨ ofelmann). Health & Place 18 (2012) 971–977