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ARE THE HABITUAL PRACTICE OF PHYSICAL ACTIVITY, DIETARY HABITS, ANTHROPOMETRIC INDICATORS, AND AUTONOMIC MODULATION ASSOCIATED WITH THE PREVALENCE OF HIGH BLOOD PRESSURE?

PRÁTICA HABITUAL DE ATIVIDADE FÍSICA, HÁBITOS ALIMENTARES, MODULAÇÃO AUTONÔMICA E INDICADORES ANTROPOMÉTRICOS ESTÃO ASSOCIADOS À PREVALÊNCIA DE PRESSÃO ARTERIAL ELEVADA?

ABSTRACT

Objective: To analyze the prevalence and association between high blood pressure, general and abdominal obesity, indicators of autonomic activity, habitual physical activity, and dietary habits in public schools in Londrina / PR. Methods: 189 subjects were evaluated (75 males and 114 females), 10-17 years. Assessment of habitual physical activity and dietary habits was performed. Anthropometric measurements were performed, in addition to measurement of resting blood pressure and heart rate variability. The chi-square test was used to assess associations between blood pressure (dependent variable) and other variables. Those that were significantly associated were submitted to Poisson regression to identify the magnitude of the association. Results: Individuals with "abdominal obesity" were 2.3 times more likely (P = 0.002) to present high blood pressure. Conclusion: Individuals with abdominal obesity are approximately twice as likely to have high blood pressure, independent of obesity levels, which in turn, are not associated with increased blood pressure.

Keywords:
Nutritional status; Autonomic nervous system; Motor activity

RESUMO

Objetivo: Analisar a associação entre pressão arterial elevada, obesidade geral e abdominal, indicadores de atuação autonômica, prática habitual de atividade física e hábitos alimentares na rede pública de ensino de Londrina/PR. Métodos: Foram avaliados 189 sujeitos (75 masculino e 114 feminino), com idade entre 10 e 17 anos. Foram realizadas avaliações antropométricas, além da pressão arterial de repouso, atuação autonômica, hábitos alimentares e prática habitual de atividade física. O teste qui-quadrado foi aplicado para verificar associações da pressão arterial (variável dependente) com as demais variáveis. Aplicou-se também a regressão de Poisson para identificação da magnitude da associação. Resultados: Obesidade e obesidade abdominal foram associadas à pressão arterial elevada. Indivíduos com obesidade abdominal obtiveram 2,3 vezes mais chance (P=0,002) de apresentarem pressão arterial elevada. Conclusão: Adolescentes com obesidade abdominal possuem aproximadamente duas vezes mais chances de apresentarem pressão arterial elevada, independente dos níveis de obesidade.

Palavras-chave:
Estado nutricional; Sistema nervoso autônomo; Atividade motora

Introduction

Arterial hypertension is highly prevalent in Brazilian adults, increasing the risk of other health complications, such as cardiovascular diseases11. [VI Brazilian Guidelines on Hypertension]. Arq Bras Cardiol. 2010;95(1 Suppl):1-51.. Similarly, overweight is ranked as the second most relevant determinant for the development of cardiovascular diseases, being only less relevant than sedentarism22. Galobardes B, Costanza MC, Bernstein MS, Delhumeau C, Morabia A. Trends in risk factors for lifestyle-related diseases by socioeconomic position in Geneva, Switzerland, 1993-2000: health inequalities persist. Am J Public Health. 2003;93(8):1302-9.,33. Christofaro DG, Andrade SM, Fernandes R, Ohara D, Dias DF, Freitas Junior IF, et al. Prevalência de fatores de risco para doenças cardiovasculares entre escolares em Londrina-PR: diferenças entre classes econômicas. Rev Bras Epidemiol. 2011;14(1):27-35.. Subjects with a high body mass index (BMI) present higher blood pressure and hence an increased risk of arterial hypertension44. Cercato C, Mancini MC, Arguello AM, Passos VQ, Villares SM, Halpern A. Systemic hypertension, diabetes mellitus, and dyslipidemia in relation to body mass index: evaluation of a Brazilian population. Rev Hosp Clin Fac Med Sao Paulo. 2004;59(3):113-8.. It is also recognized that physical inactivity is associated with the development of arterial hypertension in adults55. Eriksson J, Taimela S, Koivisto VA. Exercise and the metabolic syndrome. Diabetologia. 1997;40(2):125-35.

6. Kullo IJ, Hensrud DD, Allison TG. Relation of low cardiorespiratory fitness to the metabolic syndrome in middle-aged men. Am J Cardiol. 2002;90(7):795-7.
-77. Johnson JL, Slentz CA, Houmard JA, Samsa GP, Duscha BD, Aiken LB, et al. Exercise training amount and intensity effects on metabolic syndrome (from Studies of a Targeted Risk Reduction Intervention through Defined Exercise). Am J Cardiol . 2007;100(12):1759-66. and high blood pressure in adolescents88. Vale S, Trost SG, Rego C, Abreu S, Mota J. Physical Activity, Obesity Status, and Blood Pressure in Preschool Children. The Journal of pediatrics. 2015.. Additionally, diets rich in processed foods have also been related to high blood pressure in pediatric groups99. Kell KP, Cardel MI, Bohan Brown MM, Fernandez JR. Added sugars in the diet are positively associated with diastolic blood pressure and triglycerides in children. Am J ClinNutr. 2014;100(1):46-52..

Taking into account the large amount of scientific evidence, techniques developed to assess functions of the cardiovascular system have great relevance in the promotion of health. Among them, the assessment of the autonomic nervous system is highlighted, due to its significant action on the control of the cardiovascular system1010. Vanderlei LC, Pastre CM, Freitas Junior IF, Godoy MF. Geometric indexes of heart rate variability in obese and eutrophic children. Arq Bras Cardiol . 2010;95(1):35-40.,1111. Aubert AE, Seps B, Beckers F. Heart rate variability in athletes. Sports medicine. 2003;33(12):889-919.. The autonomic nervous system can be assessed through the use of heart hate variability (HRV) (1010. Vanderlei LC, Pastre CM, Freitas Junior IF, Godoy MF. Geometric indexes of heart rate variability in obese and eutrophic children. Arq Bras Cardiol . 2010;95(1):35-40.

11. Aubert AE, Seps B, Beckers F. Heart rate variability in athletes. Sports medicine. 2003;33(12):889-919.
-1212. Rajendra Acharya U, Paul Joseph K, Kannathal N, Lim CM, Suri JS. Heart rate variability: a review. Medical & biological engineering & computing. 2006;44(12):1031-51..

Few studies have assessed the relationship between HRV and high blood pressure in adolescents, however, they point out that higher blood pressure is related to lower activity of the autonomic system1313. Gui-Ling X, Jing-Hua W, Yan Z, Hui X, Jing-Hui S, Si-Rui Y. Association of high blood pressure with heart rate variability in children. Iranian journal of pediatrics. 2013;23(1):37-44.,1414. Zhou Y, Xie G, Wang J, Yang S. Cardiovascular risk factors significantly correlate with autonomic nervous system activity in children. Can J Cardiol. 2012;28(4):477-82., suggesting that even in young groups, the adoption of unhealthy habits seems to promote harmful physiological adaptations related to neuronal control.

It is well documented that physical activity22. Galobardes B, Costanza MC, Bernstein MS, Delhumeau C, Morabia A. Trends in risk factors for lifestyle-related diseases by socioeconomic position in Geneva, Switzerland, 1993-2000: health inequalities persist. Am J Public Health. 2003;93(8):1302-9.,33. Christofaro DG, Andrade SM, Fernandes R, Ohara D, Dias DF, Freitas Junior IF, et al. Prevalência de fatores de risco para doenças cardiovasculares entre escolares em Londrina-PR: diferenças entre classes econômicas. Rev Bras Epidemiol. 2011;14(1):27-35., food habits99. Kell KP, Cardel MI, Bohan Brown MM, Fernandez JR. Added sugars in the diet are positively associated with diastolic blood pressure and triglycerides in children. Am J ClinNutr. 2014;100(1):46-52., anthropometric indices44. Cercato C, Mancini MC, Arguello AM, Passos VQ, Villares SM, Halpern A. Systemic hypertension, diabetes mellitus, and dyslipidemia in relation to body mass index: evaluation of a Brazilian population. Rev Hosp Clin Fac Med Sao Paulo. 2004;59(3):113-8., and the autonomic nervous system1313. Gui-Ling X, Jing-Hua W, Yan Z, Hui X, Jing-Hui S, Si-Rui Y. Association of high blood pressure with heart rate variability in children. Iranian journal of pediatrics. 2013;23(1):37-44.,1414. Zhou Y, Xie G, Wang J, Yang S. Cardiovascular risk factors significantly correlate with autonomic nervous system activity in children. Can J Cardiol. 2012;28(4):477-82. are factors that affect blood pressure in isolation. However, when considering blood pressure as the outcome, the assessment of isolated and clustered effects of anthropometric, behavioral, and physiological variables could clarify the actual determinants of high blood pressure in adolescents. The use of appropriate statistical models seems to improve knowledge about covariates in this complex relationship.

Therefore, the aim of the present study was to analyze the association of blood pressure with anthropometric indices, HRV, food habits, and physical activity practice in schoolchildren from Londrina, southern Brazil.

Methods

Sample

The sample was composed of adolescents of both sexes, with ages ranging from 10 to 17 years-old, regularly registered in public elementary schools. The minimum sample size was estimated taking into account a prevalence of 10%1515. Moura AA, Silva MA, Ferraz MR, Rivera IR. Prevalence of high blood pressure in children and adolescents from the city of Maceió, Brazil. J Pediatr (Rio J). 2004;80(1):35-40., statistical power of 80%, and error of 5%. The required sample was 150 subjects. Taking into account the conglomerate sampling, the sample was increased by 20%.

Parents signed a written consent form as the inclusion criteria. The study was approved by the Ethical Research Board of the University (CAAE Nº 0281.0.268.000-07 - Report Nº 295/07).

Anthropometry

All anthropometric measures were taken with the subjects wearing light clothing and no shoes. Body mass was measured using a digital scale with a maximum capacity of 150kg, and height using a portable stadiometer. BMI was estimated dividing body mass by height squared. The cutoffs proposed by Cole et al.1616. Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. Establishing a standard definition for child overweight and obesity worldwide: international survey. BMJ. 2000;320(7244):1240-3. were used to identify nutritional status.

Food habits

Food habits were assessed through the use of a questionnaire composed of four questions, in which the adolescents reported the frequency (none; 1-2 days; 3-5 days; seven days) of consumption of several types of foods (vegetables; snacks and beverages; fruits; fried foods) in the week prior to the assessment. The response "6-7 days" was adopted as "high consumption" (categorical variable) for these types of food. The habit of skipping any meal was also assessed.

Physical activity practice

Physical activity practice was assessed using a questionnaire1717. Baecke JA, Burema J, Frijters JE. A short questionnaire for the measurement of habitual physical activity in epidemiological studies. Am J Clin Nutr. 1982;36(5):936-42.) previously validated for the Brazilian pediatric population1818. Guedes DP, Lopes CC, Guedes JERP, Stanganelli LC. Reprodutibilidade e validade do questionário Baecke para avaliação da atividade fisica habitual em adolescentes. Rev Port Ciênc Desp. 2006;6(3):265-74.. The questionnaire generates a score considering the physical activity performed at school, sport practice, leisure-time, and overall physical activity (school, sport, and leisure-time). Adolescents who were ranked in the lowest quartile for physical activity score were classified as "low physical activity practice" (categorical variable).

Waist circumference

Waist circumference was defined as the minimum circumference between the iliac crest and last rib using a metallic tape measure to the nearest millimeter (mm). The cutoffs adopted to identify "absence" or "presence" of abdominal obesity were proposed by Taylor et al.1919. Taylor RW, Jones IE, Williams SM, Goulding A. Evaluation of waist circumference, waist-to-hip ratio, and the conicity index as screening tools for high trunk fat mass, as measured by dual-energy X-ray absorptiometry, in children aged 3-19 y. Am J ClinNutr . 2000;72(2):490-5..

Blood pressure

Blood pressure was assessed through the use of an automatic device (Omron HEM 742) previously validated for adolescents2020. Christofaro DG, Casonatto J, Polito MD, Cardoso JR, Fernandes R, Guariglia DA, et al. Evaluation of the Omron MX3 Plus monitor for blood pressure measurement in adolescents. Eur J Pediatr. 2009;168(11):1349-54.. Adolescents remained seated for 10 minutes prior to the assessment. The procedures adopted for blood pressure measurement have been previously published2121. Pickering TG, Hall JE, Appel LJ, Falkner BE, Graves JW, Hill MN, et al. Recommendations for blood pressure measurement in humans: an AHA scientific statement from the Council on High Blood Pressure Research Professional and Public Education Subcommittee. J ClinHypertens (Greenwich). 2005;7(2):102-9.. The criteria to classify adolescents as "normotensive" or "hypertensive" were those established by the National High Blood Pressure Education Program2222. Program NHBPE. The fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents. Pediatrics; 2005. p. 826-7.. Adolescents ≥95 percentile for systolic and/or diastolic blood pressure were classified as "high blood pressure".

Heart rate variability

HRV was measured using a previously validated heart rate monitor (Polar - RS800CX)2323. Quintana DS, Heathers JA, Kemp AH. On the validity of using the Polar RS800 heart rate monitor for heart rate variability research. Eur J Appl Physiol. 2012(Epub ahead of print).. The R-R intervals were recorded by the device for 10 minutes and subsequently uploaded to a computer using the software Polar Precision Performance (release 3.00, Polar Electro Oy), considering only the final five minutes of measurement. Fourier's transformation was performed to quantify the very low, low, and high frequency bands, following the recommendations of the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology2424. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Circulation. 1996;93(5):1043-65.. The quantitative analysis "beat-by-beat" was performed using the Poincaré plot. The analyzed variables were RMSSD (time domain), LF, HF, and LF/HF (frequency domain). Adolescents ranked in the lowest quartile for HRV were classified as "low" HRV (RMSSD, LF, HF, and LF/HF).

Experimental design

Initially, the Municipality Department of Education provided a list of all school units in the city and their geographical location. Taking into account the geographical regions (north, south, east, west and downtown), a random process was used to select one school unit per geographical region, totalizing five. The selected school units provided a list of all schoolchildren of the target age and from this students were randomly selected. Following the previously established minimum sample size, 36 adolescents were assessed in each school unit. Only adolescents whose parents/legal guardians signed the written consent form were assessed.

Data collection began with questionnaire filling (food habits and physical activity), followed by anthropometric measures (height, body mass, and waist circumference). Next, the adolescents received guidance and help (if necessary) on how to wear the heart rate monitors used to assess HRV. HRV measures were taken in a quiet room in a supine position and the adolescents were requested not to speak and to avoid movements. After the HRV measures, the adolescents were carefully positioned in the sitting position for blood pressure measures.

Statistical analysis

Initially, the normality assumption (stratified by sex) was assessed using the Kolmogorov-Smirnov's test. Next, the Mann-Whitney U test (continuous data) was used to compare the sexes. The Chi-square test (categorical data) assessed the existence of associations of blood pressure (dependent variable) with nutritional status, waist circumference, HRV, food habits, and physical activity (independent variables). Associations with p<0.200 were analyzed in the Poisson regression to determine the magnitude of the associations between the dependent and independent variables (prevalence ratio [PR]). Statistically significant associations in the crude model were inserted in the adjusted multivariate model. Numerical variables were presented as median and interquartile range. Significance was set at P<0.05. Statistical analysis was performed using the statistical software SPSS version 17.0 and STATA version 8.

Results

The general characteristics of the sample are presented in Table 1. For anthropometric variables, boys were taller than girls (P=0.025). Systolic blood pressure was on average 6 mmHg lower in girls than boys. Boys and girls were similar in age, body mass, BMI, waist circumference, and diastolic blood pressure.

Table 1
General characteristics of the sample (numerical variables). Median and IR.

It was detected that one out of six adolescents was classified as overweight, while the obesity rate was around four percent in both sexes. The prevalence of overweight and obesity was higher in girls compared to boys. On the other hand, boys presented a higher prevalence of abdominal obesity and high blood pressure than girls (Table 2).

Table 2
Prevalence of nutritional status, abdominal obesity, and blood pressure in schoolchildren from Londrina, Parana State, Brazil.

Table 3 presents the results of the chi-square test, which tested the association of blood pressure with anthropometric indices (BMI and waist circumference), HRV indices (RMSSD, LF, HF, and LF/HF), food habits (fried foods, vegetables, snacks/beverages, fruits, skipping meals, and knowledge about food habits), and physical activity (school, sport, leisure-time, and overall).

Table 3
Association of blood pressure with anthropometric indices, heart rate variability, food habits and physical activity.

For the anthropometric indices, abdominal obesity was associated with high blood pressure, while HRV, food habits, and physical activity were not.

In the crude model (Figure 1), values of PR and the 95% confidence interval (95%CI) are presented for the association of high blood pressure with anthropometric indices (BMI and waist circumference), HRV (LF), food habits (knowledge about food habits), and physical activity (performed at school). Obese adolescents were twice as likely to present high blood pressure compared with normal weight individuals (PR=2.12[95%CI=1.06-4.21]). In the association with "waist circumference", the chance of adolescents with abdominal obesity having high blood pressure was 134% higher than non-abdominally obese adolescents (PR=2.34[95%CI=1.47-3.73]). There were no significant associations with the other independent variables.

Figure 1
Crude model of the association of high blood pressure (dependent variable) with anthropometric indices, HRV, food habits, and physical activity.

In the adjusted model (Figure 2), for anthropometric indices (BMI and waist circumference) the association between "nutritional status" and "high blood pressure" was no longer significant (PR=0.97[95%CI=0.44-2.18]). The association between "waist circumference" and "high blood pressure" remained significant, in which abdominally obese adolescents were 136% more likely to present high blood pressure (PR=2.36[95%CI=1.37-4.07]).

Figure 2
Adjusted model of the association between high blood pressure (dependent variable) and anthropometric variables.

Discussion

The present study analyzed the prevalence of high blood pressure and its associations with anthropometric indices, HRV, food habits, and physical activity in schoolchildren from public schools aged from 10-17 years in the city of Londrina. The prevalence of high blood pressure observed in this study is higher than observed in previous studies33. Christofaro DG, Andrade SM, Fernandes R, Ohara D, Dias DF, Freitas Junior IF, et al. Prevalência de fatores de risco para doenças cardiovasculares entre escolares em Londrina-PR: diferenças entre classes econômicas. Rev Bras Epidemiol. 2011;14(1):27-35.,2525. Casonatto J, Ohara D, Christofaro DGD, Fernandes RA, Milanez V, Dias DF, et al. Pressão arterial elevada e obesidade abdominal em adolescentes. Rev Paul Pediatr. 2011;29(4):567-71.,2626. Christofaro DG, Casonatto J, Fernandes RA, Reichert FF, Lock MRL, Guariglia DA, et al. Pressão arterial elevadaemadolescentes de alto níveleconômico. Rev Paul Pediatr . 2010;28(1):23-8. carried out in the same city. The increase of 16% in the prevalence of high blood pressure over the last five years is concerning, while the prevalence of high blood pressure shows a significant increase of around 10%, even when compared to the prevalence in older high school students2727. Romanzini M, Reichert FF, Lopes AS, Farias Junior JC. Prevalência de fatores de risco cardiovascular em adolescentes. Cad Saúde Pública. 2008;24(11):2573-81..

The prevalence of overweight was similar to previous studies involving Brazilian students2828. Ricardo GD, Caldeira GV, Corso ACT. Prevalência de sobrepeso e obesidade e indicadores de adiposidade central em escolares de Santa Catarina, Brasil. Rev Bras Epidemiol . 2009;12(3):424-35.,2929. Reuter CP, Burgos LT, Camargo MD, Possuelo LG, Reckziegel MB, Reuter EM, et al. Prevalence of obesity and cardiovascular risk among children and adolescents in the municipality of Santa Cruz do Sul, Rio Grande do Sul. São Paulo Med J. 2013;131(5):323-30., and the prevalence of obesity was lower2828. Ricardo GD, Caldeira GV, Corso ACT. Prevalência de sobrepeso e obesidade e indicadores de adiposidade central em escolares de Santa Catarina, Brasil. Rev Bras Epidemiol . 2009;12(3):424-35.,2929. Reuter CP, Burgos LT, Camargo MD, Possuelo LG, Reckziegel MB, Reuter EM, et al. Prevalence of obesity and cardiovascular risk among children and adolescents in the municipality of Santa Cruz do Sul, Rio Grande do Sul. São Paulo Med J. 2013;131(5):323-30.. It is noteworthy that the present study does not take into account economic condition, limiting inferences of the finding, since higher economic status is related to higher rates of overweight and obesity33. Christofaro DG, Andrade SM, Fernandes R, Ohara D, Dias DF, Freitas Junior IF, et al. Prevalência de fatores de risco para doenças cardiovasculares entre escolares em Londrina-PR: diferenças entre classes econômicas. Rev Bras Epidemiol. 2011;14(1):27-35.,3030. Wang Y, Monteiro C, Popkin BM. Trends of obesity and underweight in older children and adolescents in the United States, Brazil, China, and Russia. Am J Clin Nutr . 2002;75:971-7..

Disagreeing with other studies2929. Reuter CP, Burgos LT, Camargo MD, Possuelo LG, Reckziegel MB, Reuter EM, et al. Prevalence of obesity and cardiovascular risk among children and adolescents in the municipality of Santa Cruz do Sul, Rio Grande do Sul. São Paulo Med J. 2013;131(5):323-30.,3131. Silva KS, Farias Junior JC. Fatores de risco associados a pressão arterial elevada em adolescentes. Rev Bras Med Esporte. 2007;13(4):237-40.,3232. Hoffmann M, Silva ACP, Siviero J. Prevalência de hipertensão arterial sistêmica e inter-relações com sobrepeso, obesidade, consumo alimentar e atividade física, em estudantes de escolas municipais de Caxias do Sul. Pediatria (São Paulo). 2010;32(3):163-72. the present study did not find a significant association between obesity and high blood pressure, however when "overweight" and "obesity" were combined there was an association with "high blood pressure" (P=0.043 - data not shown). Other studies combining "overweight" and "obesity" also found significant associations2626. Christofaro DG, Casonatto J, Fernandes RA, Reichert FF, Lock MRL, Guariglia DA, et al. Pressão arterial elevadaemadolescentes de alto níveleconômico. Rev Paul Pediatr . 2010;28(1):23-8.,3333. Pinto SL, Silva RCR, Priore SE, Assis AMO, Pinto EJ. Prevalência de pré-hipertensão e de hipertensão arterial e avaliação de fatores associados em crianças e adolescentes de escolas públicas de Salvado, Bahia, Brasil. Cad Saúde Pública . 2011;6:1065-76.. In the statistical analysis, only the obese adolescents were maintained as evidence shows that "overweight" does not significantly increase the risk of diseases3434. Orpana HM, Berthelot JM, Kaplan MS, Feeny DH, McFarland B, Ross NA. BMI and mortality: results from a national longitudinal study of Canadian adults. Obesity (Silver Spring). 2010;18(1):214-8.

35. Flegal KM, Graubard BI, Williamson DF, Gail MH. Excess deaths associated with underweight, overweight, and obesity. JAMA. 2005;293(15):1861-7.
-3636. Flegal KM, Graubard BI, Williamson DF, Gail MH. Cause-specific excess deaths associated with underweight, overweight, and obesity. JAMA. 2007;298(17):2028-37..

On the other hand, in the crude models, obese adolescents were twice as likely to present high blood pressure. Regarding abdominal obesity, there was an association with high blood pressure and the magnitude observed was similar to that observed for obesity. However, in the adjusted model the association with nutritional status was no longer significant. In this sense, abdominal obesity increased twice the likely risk of high blood pressure. Previous studies have observed similar associations2525. Casonatto J, Ohara D, Christofaro DGD, Fernandes RA, Milanez V, Dias DF, et al. Pressão arterial elevada e obesidade abdominal em adolescentes. Rev Paul Pediatr. 2011;29(4):567-71.,3737. Domingos E, Domingues V, Pires Júnior R, Caldeira AS, Christofaro DGD, Casonatto J. Associação entre estado nutricional antropométrico, circunferência de cintura e pressão arterial em adolescentes. Rev Bras Cardiol. 2013;26(2):94-9.,3838. Slentz CA, Houmard JA, Kraus WE. Exercise, abdominal obesity, skeletal muscle, and metabolic risk: evidence for a dose response. Obesity (Silver Spring) . 2009;17 Suppl 3:S27-33., suggesting that increased abdominal fatness constitutes a risk factor for the development of cardiovascular complications. The risk for health related to abdominal fatness is higher than overall fatness3838. Slentz CA, Houmard JA, Kraus WE. Exercise, abdominal obesity, skeletal muscle, and metabolic risk: evidence for a dose response. Obesity (Silver Spring) . 2009;17 Suppl 3:S27-33.

39. Despres JP. Is visceral obesity the cause of the cause of the metabolic syndrome? Ann Med. 2006;38:52-63.
-4040. Despres JP, Lemieux I. Abdominal obesity and metabolic syndrome. Nature. 2006;444(881-7)., which is concerning due to the increase in the waist circumference of adolescents in recent years4141. Li C, Ford ES, Mokdad AH, Cook S. Recent trends in waist circunference and waist-height ratio among US children and adolescents. Pediatrics. 2006;118(5):1390-8..

The association between abdominal fatness and high blood pressure, even without clear pathways so far, seems to be supported by imbalances in insulin sensitivity, with compensatory hyperinsulinemia4242. Nieves DJ, Cnop M, Retzlaff B, Walden CE, Brunzell JD, Knopp RH, et al. The atherogenic lipoprotein profile assocated with obesity and insulin resistance is largely attributable to intra-abdominal fat Diabetes. 2003;52:172-9.,4343. Cnop M, Landchild MJ, Vidal J, Havel PJ, Knowles NG, Carr DR, et al. The current acumulation of intra-abdominal an subcutaneous fat explains the association between insulin resistance and plasma leptin concentrations. Diabetes. 2002;51:1005-15.. Due to excessive insulin secretion, blood pressure increases, since insulin secretion stimulates sodium and hence water retention, leading to higher sympathetic activity4444. Caprio S, Tamborlane WV. Metabolic impact of obesity in childhood. Endocrinol Metab Clin North Am. 1999;28:731-47.. Abdominal fatness is also related to higher blood concentration of fat-free-acids, leading to body fatness accumulation and lower sensitivity of the liver and skeletal tissues to insulin action4545. Phillips DI, Caddy S, Ilic V, Fielding BA, Frayn KN, Borthwick AC, et al. Intramuscular triglyceride and muscle insulin sensitivity: evidence for a relationship and nondiabetic subjects. Metabolism. 1996;45:947-50.,4646. Ferranniini E, Barrett EJ, Bevilacqua S, DeFronzo RA. Effect of fatty acids on glucose production and utilization in man. J Clin Invest. 1983;72(5):1737-47..

There was no association between high blood pressure and HRV indices. The absence of association could be supported by the low number of obese adolescents in the sample. Previous studies identified an association between autonomic modulation and obesity in children1010. Vanderlei LC, Pastre CM, Freitas Junior IF, Godoy MF. Geometric indexes of heart rate variability in obese and eutrophic children. Arq Bras Cardiol . 2010;95(1):35-40.,4747. Baum P, Petroff D, Classen J, Kiess W, Bluher S. Dysfunction of autonimic nervous system in childhood obesity: a cross-sectional study. PLoS One. 2013;8(1):e54546.,4848. Kaufman CL, Kaiser DR, Steinberger J, Kelly AS, Dengel DR. Relationships of cardiac autonomic function with metabolic abnormalities in childhood obesity. Obesity (Silver Spring) . 2007;15(5):1164-71.. There are few data about the relationship between blood pressure and HRV in children. In the study conducted by Zhou et al.1414. Zhou Y, Xie G, Wang J, Yang S. Cardiovascular risk factors significantly correlate with autonomic nervous system activity in children. Can J Cardiol. 2012;28(4):477-82.) there was an association between obesity and reduced activity of the vagus nerve, as well as an association between high blood pressure and modifications in vagal and sympathetic activity. The differences between the studies could be attributed to differences in the analyzed sample as well as the methods/classifications used for HRV.

In the present study, physical activity was not related to high blood pressure, agreeing with previous studies involving pediatric groups3131. Silva KS, Farias Junior JC. Fatores de risco associados a pressão arterial elevada em adolescentes. Rev Bras Med Esporte. 2007;13(4):237-40.,3232. Hoffmann M, Silva ACP, Siviero J. Prevalência de hipertensão arterial sistêmica e inter-relações com sobrepeso, obesidade, consumo alimentar e atividade física, em estudantes de escolas municipais de Caxias do Sul. Pediatria (São Paulo). 2010;32(3):163-72.. Recent studies4949. Moraes ACF, Carvalho HB, P. R-LJ, Gracia-Marco L, Beghin L, Kafatos A, et al. Independent and combined effects of physical activity and sedentary behavior on blood pressure in adolescents: gender differences in two cross-sectional studies. PLoS One . 2013;8(5):e62006.,5050. Martinez-Gomes D, Ortega FB, Ruiz JR, Vicente-Rodriguez G, Veiga OL, Widhalm K, et al. Excessive sedentary time and low cardiorespiratory fitness in european adolescents: the HELENA study. Arch Dis Child. 2011;96:240-6. have identified that sedentary habits is the main behavioral variable related to the development of cardiovascular risk factors, such as increased blood pressure. Therefore, physical activity and sedentary habits have to be considered as independent variables5151. Ekelund U, Brage S, Froberg K, Harro M, Anderssen SA, Sardinha LB, et al. TV viewing and physical activity are independently associated with metabolic risk in children: the european youth heart study. PLoS One . 2006;3(12):e488.. In this sense, it is noteworthy to recognize that sedentary behaviors were not assessed in this study.

The association between high blood pressure and food habits was also not significant, similar to other studies2626. Christofaro DG, Casonatto J, Fernandes RA, Reichert FF, Lock MRL, Guariglia DA, et al. Pressão arterial elevadaemadolescentes de alto níveleconômico. Rev Paul Pediatr . 2010;28(1):23-8.,3131. Silva KS, Farias Junior JC. Fatores de risco associados a pressão arterial elevada em adolescentes. Rev Bras Med Esporte. 2007;13(4):237-40.. It is necessary to highlight the limitations related to the assessment of food habits through the use of the available tools, which usually have low reliability, particularly in children and adolescents. Moreover, our questionnaire assessed only weekly frequency instead of the amount of consumed food.

Obesity seems to be the most relevant condition related to the increase in blood pressure in adolescents, since other variables related to higher blood pressure in previous studies were not significantly related to high blood pressure in our multivariate model.

It is relevant to highlight that blood pressure was assessed in one opportunity in the present study and due to the effects of behavioral, nutritional, and emotional factors on blood pressure control, the inferences for arterial hypertension diagnosis should be avoided. Moreover, only adolescents from public schools were assessed, limiting generalizations to adolescents from private schools. Additionally, the cross-sectional design of the study does not offer support for causality relationships, and future research should take into account other nutritional variables related to the cardiovascular system, such as sodium and caffeine.

The present study did not assess biological maturation of the adolescents, which is a limitation. However, it is important to remember that blood pressure has been not related to sexual maturation when the effects of body mass and height are controlled5252. Gaya AR, Cardoso M, Gaya A, Santos P, Oliveira J, Ribeiro J, et al. Efeitos da maturação sexual nos níveis de pressão arterial em crianças e adolescentes do sexo masculino: associação com as variáveis massa corporal, estatura e idade cronológica. Rev Bras Educ Fis Esp. 2005;19(3):199-207.. Therefore, blood pressure in adolescents should not be determined by sexual maturation stages. Moreover, maturation is not considered in the construction of the percentile values to diagnose high blood pressure in children and adolescents2222. Program NHBPE. The fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents. Pediatrics; 2005. p. 826-7..

Conclusions

Abdominally obese adolescents present two times higher odds for high blood pressure, independent of general obesity, which in turn was not related to blood pressure. HRV indices, food habits, and physical activity were not associated with high blood pressure in the analysed schoolchildren.

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Publication Dates

  • Publication in this collection
    2016

History

  • Received
    05 Mar 2015
  • Reviewed
    28 Feb 2016
  • Accepted
    12 Mar 2016
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