Prevalence of Elevated Arterial Pressure and Associated Risk Factors in 10 to 15 Year Old Students from the Municipality of Cajazeiras-PB , Brazil

Background: Overweight and obesity are rising in developing countries among all age groups. Children and adolescents are, therefore, exposed to higher risk of developing hypertension. Early identification can help avoiding or lessening complications through the life span. In order to plan adequate prevention programs, cities need to identify the prevalence of such condition. We aimed to identify the prevalence of Elevated Arterial Pressure (EAP) and associated factors in students from the municipality of Cajazeiras-PB, Brazil, a region in the Northeast of Brazil.


Introduction
Hypertension (HTN) is a syndrome mainly characterized by high systemic arterial blood pressure associated with cardiovascular, metabolic and hormonal changes [1].Health of people worldwide is affected by HTN, which is considered one of the main modifiable associated factors of mortality by cardiovascular disease and stroke.Although HTN is more frequent in the elderly and adults [1], the prevalence of Elevated Arterial Pressure (EAP) in children and adolescents have been on the raise [2], ranging from 2.3% to nearly 8.0% in Brazil [3,4].Research indicate that children with EAP are 2.4 times more likely to become adults with HTN [2].Studies with students suggest that variability of arterial blood pressure levels depends of factors such as age, abdominal circumference and increased Body Mass Index (BMI) [2,3,5].
In many cases, HTN is not associated with clinical symptoms, being considered a silent disease.Its detection is only possible through regular blood pressure monitoring.Measurement of arterial pressure in children and adolescents has been recommended at every clinical assessment after age three, at least annually as part of primary care, and must follow the standards established for adults.[1] Interpretation of Systolic Arterial Pressure and Diastolic Arterial Pressure readings in this population must take into account age, gender, and height according to the guideline of The Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents.[4] There are few studies in Brazil describing prevalence of EAP among children and adolescents in Brazil.Specifically, we did not identify any study on the municipality of Cajazeiras, in the estate of Paraíba (PB), Brazil, located in the Northeast of the country.Understanding the prevalence of EAP among students in this region is important to promote early detection and adequate intervention.Thus, this study aimed to determine EAP prevalence and associated risk factors among 10 to 15-year-old students from the municipality of Cajazeiras-PB, Brazil.

Study design and sampling method
We conducted a cross-sectional study with 10 to 15-year-old students from urban and rural areas of the Brazilian municipality Cajazeiras-PB, between September and October, 2011.We identified 33 target schools to be part of the sample using data from the city and state Secretaries of Education and Culture.Sample calculation was based on previous studies, considering the lowest prevalence rate of 1.2%, and anticipating a 15% sample loss.We used a multi-stage random sampling to select 11 schools and students in 6 th to 9 th grade.The final sample was proportional to the percentage of students enrolled in the study regions.

Data collection
General information.We used the Global-based Student Health Survey to assess adolescents' exposure to health-risk behaviors [6].This survey has sections on demographics (e.g.: gender, age, re-of arterial pressure is important to early identification of EAP in this population.Stake holders in the state of Paraiba, Brazil, should include this monitoring in the protocol of pediatric visits in public health facilities.sidential area), socioeconomic characteristics, and life characteristics (e.g.: exposure to tobacco and alcohol, dietary habits, practice of physical activities).
Anthropometric measurement.Height and weight were measured with a portable scale (Toledo).We followed the Centers for Diseases and Control and Prevention guidelines to collect data on waist circumference (WC) and BMI [7].
Arterial blood pressure.After five minutes of rest, Systolic Blood Pressure (SBP) and Diastolic Blood Pressure (DBP) were measured on the right arm, twice in a single visit, with a 2-minute interval; the lowest values were recorded.We classified as EAP measures for SBP and/or DBP equal or greater than the percentile 95 at reference tables for children and adolescents.Prevalence of EAP was estimated according to widely used criteria [8].All measuring instruments were calibrated following the norms of the Brazilian National Institute of Metrology, Quality and Technology (Inmetro).

Statistical analysis
Data analysis were performed using Stata/IC 12.1 software.As data were not normally distributed, we used Mann-Whitney and Chi-Square/Fisher's exact tests to describe the data and investigating associations among EAP and study variables.To look at these associations, we used the criterion providing the highest prevalence (SBP or DBP elevated) to increase statistical power.We run a multiple logistic regression model using as independent variables those associated with EAP in the bivariate analysis.Statistical significant level was set to .05.

Ethical aspects
This study was approved by the Institutional Review Board of the Health Sciences Center, Universidade Federal da Paraíba, Brazil (#035/11).

Results
Among all participants, 55.4% were females and 47% were self-classified, in terms of race/skin color, as "pardo"(brown).Average age was 12.8 years (SD: 1.38) and predominant monthly family income was one to four minimum wage (64.4%).Around 77% lived in urban area and the majority of households (59.3%) had four to six people.Mean values for WC and BMI were 70.9 cm (SD: 9.7) and 19.4 kg/m 2 (SD: 3.8).Average SBP was 101.0 mmHg (SD: 12.4), while average DBP was 65.9 mmHg (SD: 9.5).Table 1 presents sociodemographic, behavioral, and clinical characteristics of participants for the total sample, as well as bivariate association according to the presence of EAP.
Comparison between individuals with and without EAP showed no association with gender, age, race/ skin color, residence area, religion, monthly family income, and number of people living in the household (Table 1).Among individuals with EAP, 16.7% had experienced at least one episode of hunger in the past compared to 4.5% of those without EAP (p= .026).EAP was also associated with exposure to tobacco (p= .022),as well as high WC (p=.001) and high BMI (p=.003) (Table 1).Students 13-to 15-year old presented higher SBP average compared to the 10-to 12-year old group.However, the difference was statistically significant only for males (p < .05)(Table 2).
According to the bivariate analysis, episodes of hunger in the past, exposure to tobacco, waist circumference, and BMI were associated with EAP.Thus, we modeled a multinomial logistic regression using these four variables as predictors of EAP.We found statistically significant association among ex-

Discussion
Prevalence of EAP in this study was 3.5%, which is within a range of 1.2 to 13% observed in previous similar studies.In bivariate analysis, we observed that EAP was associated with exposure to tobacco, experience of hunger in the past, high WC and BMI.
In out multivariate model, students exposed to tobacco or who ever experienced hunger were more likely to present EAP.
A study in the United States found a prevalence of 2.7% for elevated systolic blood pressure and 2% for elevated diastolic blood pressure among 10-to 15-year old students [3].In South Africa, the variation was from 2.3% to 5.9% [9].In Brazil, prevalence rates varied between 2.3% [4] and 7.7% [10].Several factors influence the variability in these prevalence, such as time when blood pressure was measured and number of subjects from different age groups [11].
Participants with EAP reported more episodes of hunger in the past.Although our confidence interval is wide (95% IC: 1.134-12.256)and our results need to be interpreted with cautious, it has been suggested that hypertension is more frequent among the poorest [12] and experience of hunger is a proxy for lower socioeconomic status.Average values for SBP and DBP were higher for 13-to 15-year old males compared to their younger peers (Table 3).This difference is statistically significant and clinically relevant given that essential hypertension tends to be more frequent among adolescents and young adults [13].
We found a significant association between exposure to tobacco and EAP in exploratory multivariate analysis.A link between EAP and tobacco exposure has been described before [10,14].Tobacco use is considered the lead cause of mortality   in cardiovascular diseases.Quitting the habit does not reduce pressoric levels, but reduces cardiovascular risks [1].The habit of smoking tobacco usually starts during childhood.A study conducted in the south region of Brazil reported a prevalence of 12.1% of tobacco use among children and adolescents between ages 10 and 19 [15].In the same study, the authors found that 75% of subjects with elevated arterial blood pressure were exposed to tobacco.
We also observed, in bivariate analysis, an association between EAP and BMI, as described by other authors [16].Although the significance did not hold in the multivariate analysis, relationship between EAP and obesity has been reported in epidemiologic studies with children and adolescents [16,17].Larger WC has been associated with reduced HDL cholesterol, as well as increased triglycerides, EAP, and left ventricular volume, as observed in adults [18].Implication of this finding is worrisome because obese children and adolescents are at higher risk to present HNT in adulthood and more likely to develop cardiovascular disease [4].
As any other studies, ours had strengths and limitations.We used a prospective design and the computed sample size was inflated, which allowed to collect information for the estimated sample size.This approach reduces information bias in our results.Moreover, in combination with the stratification of the sample proportionally to the percentage of students enrolled in the study regions, this sample can be considered representative of students between ages 10 and 15 enrolled in the school system of the municipality of Cajazeiras-PB, Brazil in the academic year of 2011.An important limitation of our study is the inability of making inferences of causality because of its cross-sectional design; the associations presented are only exploratory.Some categories in the multivariate analysis had small cell sizes (between four and six observations).Therefore, results should be interpreted cautiously.Data presented here, however, can be used to support designing specific programs to monitor arterial pressure in children and adolescents, as well as to inform future studies in this municipality.

Conclusion
To sum up, this study found that prevalence of EAP among students from the municipality of Cajazeiras-PB is within the average observed among Brazilian students.EAP was especially associated with exposure to tobacco and episodes of hunger in the past.Current findings add to a growing body of literature on the importance of assessing arterial blood pressure in students because high values are predictors of HNT and associated complications through the life span.
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International Archives of Medicine is an open access journal publishing articles encompassing all aspects of medical science and clinical practice.IAM is considered a megajournal with independent sections on all areas of medicine.IAM is a really international journal with authors and board members from all around the world.The journal is widely indexed and classified Q1 in category Medicine.
The difference column presents results of chi-square or Fisher exact's test (categorical variables) or Mann-Whitney (continuous variables).An asterisk (*) indicates statistical significance (p < .05).SD = Standard deviation; MW = Minimum wage; WC = Waist Circumference; BMI = Body Mass Index; SBP = Systolic Blood Pressure; DBP = Diastolic Blood Pressure posure to tobacco, episodes of hunger in the past and EAP (Table3).

Table 2 .
Comparison among mean systolic blood pressure, diastolic blood pressure according to age categories and gender for 690 students, 10-to-15-year-old, of Cajazeiras-PB, Brazil.