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  • The HELENA study was based on data from a random sample of European adolescents who were tested on a wide range of nutrition and health-related parameters. The data were collected in 2006 and 2007 in ten cities from nine European countries. A detailed description of the HELENA sampling and recruitment methodology, harmonization processes, data collection, analysis strategies and quality control activities has been published elsewhere [12]. After receiving complete information about the aims and methods of the study, all parents/guardians signed an informed consent form and the adolescents agreed to participate in the study. The protocol was approved by the Human Research Review Committees of the centers involved. Data from the BRACAH study were collected in 2007 in the city of Maringá, PR, Brazil, population approximately 330,000 (51,428 adolescents, 50.1% female). The adolescents were selected by random sample and evaluated on a broad range of cardiovascular risk factors and various health behavior parameters. The complete sample size methodology of this study has been described previously [13]. A formal request to conduct this survey was submitted to and accepted by the boards of several public and private schools. This study was also approved by the Ethics Committee on Research Involving Human Participants of the University Center of Maringá and authorized by the Ethics Committee on Research Projects of the University of São Paulo in accordance with Brazilian laws. For the current study, we selected adolescents from HELENA and BRACAH with complete data regarding gender, age, systolic BP (SBP), diastolic BP (DBP) (outcomes), PA levels, SB, socioeconomic status, parental education, regular tobacco consumption, body mass index and waist circumference. These variables are described in detail below. A total of 3,308 adolescents from the HELENA study (12.5–17.5 years old) and 991 adolescents from the BRACAH study (14.0–17.5 years old) met all the inclusion criteria and were included in the analyses. In both studies, BP measurements were performed following the recommendations for adolescent populations [14]. In both studies BP was measured twice after weight and height measurements were taken. The subjects were seated in a separate, quiet room for 10 min with their backs supported and feet on the ground. Two BP readings were taken with a 10 min interval of quiet rest. The lower of the two measurements was used. Systolic and Diastolic BP were measured by the arm blood pressure oscillometric monitor device OMRON® M3 (HEM 742) in the BRACAH study and the OMRON® M6 (HEM 70001) in the HELENA study. The OMRON® M3 (HEM 742) has been clinically and epidemiologically validated for adolescents by the Brazilian Research Group[15]. The OMRON® M6 (HEM 70001) has been approved by the British Hypertension Society [16]. These data collection procedures have been described in an earlier study [17]. The PA and SB levels were considered independent variables and measured by means of questionnaires in both studies. The questionnaire model used for PA measurements in both studies was developed to assess PA levels (moderate-to-vigorous levels) in adolescents [18]. In the HELENA study, PA was also measured with accelerometers (Actigraph MTI, model GT1M, Manufacturing Technology Inc., Fort Walton Beach, FL, USA) for seven consecutive days, with a minimum of 8 hours recording/day for at least 3 days [19]. The time sampling interval (epoch) was set to 15 seconds. Inactive, moderate and vigorous PA was defined as <100, 2000–3999 and ≥4000 counts per minute, respectively. The cutoffs selected were similar to those used in previous studies [20], [21]. In both methodologies (questionnaire and accelerometry), and following current PA guidelines, [22], [23] subjects were classified as active when they accumulated at least 60 min/d of moderate-to-vigorous PA. Sedentary behavior levels were assessed with a structured questionnaire, including questions on time habitually spent in front of the television, the computer and/or playing video games. In both studies, the questionnaire used questions such as "During weekdays, how many hours do you usually spend watching television? "-"During weekdays, how many hours do you usually spend on computers?-"During weekdays, how many hours do you usually spend playing video games?" Sedentary behavior was totaled and classified into the following categories: 0–2 h/d; >2–4 h/d; ≥4 h/d according to Dunstan et al. [24]. The same questions were asked for weekend days and this questionnaire was used with adolescents from both studies as a realiability, validity and translated tool [25]–[27]. We also established six clusters of PA according to PA recommendations [22], [23] and SB according to Dunstan et al. [24] for use with both measurement methods, which are described below. <60 min/d of PA +>4 h/d of SB;<60 min/d of PA +2–4 h/d of SB;<60 min/d of PA +<2 h/d of SB;≥60 min/d of PA +>4 h/d of SB;≥60 min/d of PA +2–4 h/d of SB;≥60 min/d of PA +<2 h/d of SB;Accelerometer (using PA recommendations and tertiles of sedentary time): <60 min/d of PA of PA +3rd tertile of SB;<60 min/d of PA +2nd tertile of SB;<60 min/d of PA +1st tertile of SB;≥60 min/d of PA +3rd tertile of SB;≥60 min/d of PA +2nd tertile of SB;≥60 min/d of PA +1st tertile of SB; The potential confounders for this study were: Country (HELENA only):Age (years):Socioeconomic status: based on the family's household goods. In the HELENA study, the same definitions were used in previous HELENA studies [28], [29]. In the BRACAH study, the Brazil Criterion of Economic Classification [30] was employed. Three levels were used to classify socioeconomic status: low, medium and high.Parental education: determined with a self-reported questionnaire and classified into four levels: elementary education, lower secondary education, upper secondary education and university degree.Regular tobacco smoking: defined as the regular consumption of at least one cigarette per day for a minimum of one month [31];Body mass index (BMI): calculated as weight (kg)/height(m2). BMI was used as a continuous variable in the analysis. Wearing light clothes and no shoes, the adolescents' height was measured to the nearest 0.1 cm with a wood stadiometer and their body mass to the nearest 0.1 kg with a calibrated portable digital scale.Waist circumference: measured in both studies at the midpoint between the lowest point of the rib cage and the top of the iliac crest next to skin with a non-elastic measuring tape to the nearest 0.1 cm. The descriptive analyses were presented as means (quantitative variables), percentages (qualitative variables) and 95% confidence intervals (CI95%). Multilevel linear regression models using fixed effects intercept were fitted to analyze the relationship between each BP level and independent variables [32], [33], considering two levels of data organization: (i) individual behaviors and (ii) potential confounders (not shown) [34]. The context variable used was the school. Homoscedasticity was graphically assessed in all regression models to meet the analysis criteria. p-values of ≤0.20 were adopted in the univariate analysis [34] since they were necessary to include variables in the multivariate analysis and then the hierarchical model method according to the above-mentioned levels. P-values <0.05 or those representing >10% modification in the β of any variable already in the model were considered significant. The multilevel analyses were performed with two objectives: 1st) to test the associations between BP and two separate measures of individual behavior; 2nd) to test the extent to which country-specific characteristics and contextual variables mediate the associations between SBP and DBP levels and PA and SB. Stata 12 (Stata Corp., College Station, TX, USA) was used for all statistical calculations. All analyses were adjusted for the clustered nature of the sample using the "svy" set of commands and stratified by gender, since interactions between sex and the studied variables were observed (p<0.001). For adolescents from the HELENA study (boys  = 1,106; girls  = 960) we conducted a comparative analysis between the PA and SB levels found with the questionnaires and the PA measures found with and without the use of accelerometers. No significant differences were found for either sex (p = 0.406 for boys and p = 0.714 for girls).
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