Print version

SUMMARY

Introduction: The prevalence of hypertension in children is 1-3% in childhood and reaches 10% in adolescence. Body weight has a direct relationship with blood pressure, and its association with high blood pressure has been documented in different age groups. Objective: To evaluate the association between hypertension and anthropometric variables in adolescents from public and private schools in the city of Salta. Material and Methods: A cross sectional study. School adolescents, 16 to 20 years, evaluated in 2009. Variables: Blood Pressure, Body Mass Index (BMI), waist circumference (WC) and  WC / Height Ratio . Education: Public / private. Statistical analysis: Student test, Chi square, Fischer, Logistic regression. SPSS 15 Program. Results: The final sample was composed of 395 students from 5 public schools and 3 private. Logistic regression models adjusted for sex and school type showed that the probability of hypertension was 7.85 in adolescents with overweight / obesity in relation to normal nutrition status and 4.43 and 6.06 times in the WC and WC / Height Ratio increased. Also there was a higher probability of hypertension in men (OR between 4 and 5). Conclusions: It confirms the presence of a current health problem in adolescents: Hypertension, closely related to weight gain. The three indicators of obesity analyzed showed significant association with the presence of the disease.

Key words:Adolesecense. Arterial hypertension. Anthropometric variables.

Rev Fed Arg Cardiol. 2012; 41(2): 96-102

Introduction

The prevalence of hypertension (HTN) in childhood is 1-3% and reaches 10% in adolescence [1]. It has been proved that blood pressure in this stage of life follows a dragging pattern which continues until the third or fourth decade. It may result in a risk indicator for hypertension in adults and the early introduction of strategic interventions may lead to a reduction in its high prevalence in adulthood.

Obesity in childhood and adolescence is increasing in an alarming fashion both in developed and developing countries. In a recent paper that included epidemiological studies from different countries, it was reported that 1 every 5 children in the world have overweight and 2.0%-3.0% of the population between 5-17 years of age, obesity [2]. Body weight is directly related to blood pressure, and the association between BMI with high pressure has been documented in different age groups, being the most important determinant for HTN in children and adolescents, besides being a predisposing factor for adulthood [3]. Students located in the top decile of BMI have a greater prevalence of high pressure in comparison to those in the bottom decile [4].

BMI is the parameter used most frequently to determine the degree of overweight, although there are numerous papers that establish that the risk of morbidity is associated not with the increase in body fat per se, but with the increase in fat in the abdominal area, specifically with intra-abdominal fat. Waist circumference (WC) is a useful measure for abdominal obesity and is more closely related to the risk factors of CVD than obesity [5], besides the distribution of the rathertrunk fat mass (android distribution) is associated to an increase in systolic BP and left ventricular mass [6]. In turn, WC/height ratio was used for the first time in the Framingham Study [7], and different investigations [8,9] concluded that the WC/height ratio is more strongly associated to risk factors of CVD than body mass index.

For all these reasons, it is important to consider anthropometry as a useful tool, not only in evaluating the risk associated to the nutritional state per se, but also to that of other disorders, such as blood pressure increase.

Objective
To analyze in adolescents in high school in the city of Salta, Argentina, the association between hypertension and anthropometric variables.

Material and methods
Transversal, descriptive study. The data were obtained from the registries of the Project on Cardiovascular Risk Factors in school adolescents from the city of Salta [10], in which considering a prevalence estimated in 5.0% for hypertension (3%-7%), confidence interval 95%, and considering a registration of 6,000 students in the last course of the polymodal level (high school) from the capital city of Salta (year 2009), a sample of 424 students was estimated. With the aim of maintaining the distribution of students according to public or private schools (registration: 64.0% and 36.0% respectively), a simple random draw was carried out, with five public and three private institutions being chosen. All adolescents in the last course(s) of each selected school were evaluated.

Studies were made in schools by professionals and technicians from the National Center of Nutritional Investigations, with a prior authorization by the director and a consent signed by parents and students.

The following were exclusion criteria: the students that did not accept the invitation to participate in this project, those not authorized, those who reported having diseases (diabetes, heart diseases, hypertension), known eating disorders (bulimia, anorexia), pregnant girls and fast of less than 10 hours.

Ethical aspects:The study had the support of the Committee on Bioethics of the National Institute of Epidemiology “Dr. Juan H. Jara” (National Administration of Institutes and Health Laboratories, ANLIS).

Variables
Blood pressure: technique: a digital blood pressure monitor, with the brand Microlife BP 3BTO-A, automatic, the method of measurement of which is validated by the British and European Societies of Hypertension. An average was made between two pressure measurements with a 15-minute interval. The criteria for Hypertension were: tables of blood pressure according to gender, age, and height of the American Academy of Pediatrics (Task Force) [11].

HTN in adolescents from 16-17 years old: systolic blood pressure (SBP)/diastolic blood pressure (DBP) ≥95th pc [1].
HTN in adolescents ≥18 years old: ≥140/90 mmHg [12].

A pilot test was conducted to standardize and determine the variability of intraobserver and interobserver measurements by comparison of measurements (Student-t) and intraclass correlation coefficient.

Body mass index (BMI): Technique: weight; scale of the Cam type, capacity 150 kg, very few clothes, no shoes, recorded in kg and g. Height: standing, metallic tape measure graduated in cm and mm, recorded in cm and mm [13].

Tables of z score of BMI according to gender and age (WHO)[14], 16-18 years old: malnutrition ≥-2DE; normal nutrition: -2 to  +1DE; overweight ≥+1DE, obesity ≥+2DE; >19 years old: malnutrition <18.5; normal ≥18.5 <25; overweight ≥25<30; obesity ≥30 (WHO) [15].

Abdominal circumference (WC): Technique: flexible tape measure, inextensible, graduated in millimeters. With the patient standing, arms relaxed at the sides of the body, measurement in the middle point between the costal margin and the iliac crest, in exhalement. Cutoff points ≥80 cm in women; ≥94 cm in men (WHO) [16].

WC/height index:<0.5 normal; ≥0.5 increased.

Measurements were made by anthropometrist nurses and were standardized to have a mistake not higher than 100 g in weight and 0.49 cm in height.

School regime: Public/private.

Statistical analysis:The results are presented in tables and graphs of frequency and association distribution, and comparison of averages, Chi square, Fisher, Student’s t test. Multivariate logistic regression analysis: risk estimations are estimated by Odds Ratio (OR with CI 95%, p<0.05). Statistical program SPSS 15 (Window version).

Results
The final sample was constituted by 247 students from 5 public schools (134 females; 114 males, average age 17.6±0.8 years old) and 147 from 3 private schools (93 females and 54 males, average age 17.2±0.4 years old), a total of 395 students; 8 (1.7%) did not complete their studies and 63 (13.5%) had parents who did not authorize the participation of their children.

A general prevalence of hypertension of 11.4% (n=45) was verified. In adolescents from public schools, it was 10.9% (n=27) and 12.2% in private schools (n=18); in females it was 5.7% (n=13) and in males, 19.0% (n=32). The prevalence of hypertension for both genders was not statistically different, whether they belonged to a private or public school.

Table 1: The prevalence of increased BMI, WC and WC/Height was not different in the analysis of females and males according to the type of school. Due to the low prevalence of malnutrition surveyed in the analysis, in the analysis it was regrouped along with those with normal nutrition. The general prevalence of overweight and obesity in women was 14.9 and 3.5 and in males 15.5 and 3.6 respectively.

Table 2: In females and males from public schools, the averages of SBP were significantly higher, according to the cutoff points in all anthropometric variables considered. In private schools, significant differences were observed with the BMI variable, in the averages of SBP for women and SBP and DBP for men.

Table 3: The prevalence of HTN in females only resulted significantly higher by BMI in women in private schools. In males from public schools, the prevalence was significantly higher according to all variables, while in private schools just according to BMI.

Table 4: Different models were analyzed for each anthropometric variable, by the correlation existing between them, adjusted according to gender and school regime. Multivariate logistic regression models showed that the chance of hypertension was 7.85 times for adolescents with overweight/obesity in relation to those with normal nutrition and 4.43 and 6.06 times in those with increased WC and WC/height. Likewise, a greater probability of hypertension was associated to the male gender (OR between 4 and 5).

Discussion
Three indicators of obesity were analyzed in regard to the presence of hypertension in adolescents; all of them showed a significant association and corroborated that the increases in BMI and waist circumference are good risk predictors, also adding the waist/height ratio.

This paper shows a general prevalence of hypertension of 11.4% with no significant differences whether in public or private schools, although there is a marked predominance in males (19.0%). The Consensus of the Argentine Society of Pediatrics establishes that the prevalence of HTN ranges around 10% in adolescence. The real prevalence for the country and for this age group is unknown; however, data from the last specific studies performed in our country show higher figures of HTN prevalence, with differences between males and females. In Avellaneda, province of Buenos Aires [17] (year 2000), the prevalence of HTN was 4.7% in women and 13% in men; in turn, in students from high schools from the autonomous city of Buenos Aires [18] the prevalence about the 95th pc was 6.4% in women and 11.3% in men. In Corrientes [19], the prevalence of HTN was 13.4% in 10-15-year-old students, and in Misiones [20] (year 2005) in adolescents from 11-20 years old a prevalence was detected of 15.8% (9.4% in females and 25.4% in males).

Studies in different populations in the world have shown that the increase in hypertension in children and adolescents is significantly associated to an increase in body weight. Our data on overweight and obesity are still somehow above those surveyed in Misiones [19], where the prevalence in women (14%) and in men (15.9%) was observed, although with a similar tendency. The number of young people with overweight problems increases continually, with the increase in health problems that lead to this situation [21], and in adolescents from Salta, the probability of HTN associated to overweight was 7.85 times greater (CI 3.90-15.78). An even greater prevalence was observed in our comparison paper of female adolescents between 15 and 18 years old in Norway and Argentina, in which obesity was strongly associated to the prevalence of hypertension in both populations (OR 11.4 CI 1.6-82.0; OR 28.3 IC 11.8-67.7) [22] and in USA (2003-2006), where children and adolescents with obesity presented a significant risk of having HTN (males 13-17 years old, OR 9.62 IC 4.86-19.06; females OR 2.33, CI 1.31-4.13) compared to those with normal weight [23].

Although BMI was traditionally the method of choice to evaluate the nutritional state in epidemiological studies, alternative measurements such as WC, waist-hip ratio and waist-height ratio have been suggested as superior to predict the risk of cardiovascular disease. This is so, because the accumulation of abdominal fat is strongly associated to a series of metabolic alterations [24,25].

In the population of students being evaluated, WC and WC/Height index show a significant association with the prevalence of hypertension (OR 4.43 and 6.06), which coincides with the data from a recent paper about German adolescents from 12 to 18 years of age, in whom the grouping of risk factors was 3-4 times more frequent in those with central obesity, predicting in a significant way the greater risk for non-anthropometric factors of CVD, among them hypertension (OR 2.5) [26]. In another representative sample of 4811 Iran students from 6 to 18 years old, BMI and the WC/Height index were the most appropriate anthropometric measures to predict CVD risk factors, concluding that they are useful as a screening tool to identify young people in high risk [27].

The strong association between the alteration in body weight and hypertension is a proven fact. The mechanisms that justify this association are several, although abdominal obesity in the present plays an essential role in the pathogenesis of hypertension associated to overweight, from there the significance of a proper use of the indicators of adiposity.

Limitations
One of the main limitations of the present study is its transversal design, which does not allow to make inferences of causality; the characteristic of the sample can be added to this, since it restricts the results to the population studied. Although the clinical and biological evidence may lead us to assume that body weight is a determining factor for hypertension, only longitudinal studies that would allow evaluating its evolution would confirm this association.

A fact to be highlighted is the high prevalence of hypertension found, which could very well be related in part, to the fact of not making measurements in the subsequent days.

Conclusions
The strong association of hypertension with the increase in body weight confirms the presence of a vital public health problem in adolescents. The three indicators of obesity analyzed show a significant association in regard to the presence of disease. BMI, WC and WC/Height are low cost indicators and easy to apply in the evaluation of the health state of young people, and the altered presence of these indicators is related with a higher chance of developing the disease.

Acknowledgement
The National Center of Nutrition Investigations and the ANLIS, that provided the chance of conducting this study, as part of the activities of the Master’s Degree on Epidemiology in Public Health, ANLIS-FIOCRUZ agreement.

To the nurses of the CNIN, who surveyed the anthropometric and blood pressure data in the field.

REFERENCES

1. Consenso sobre factores de riesgo de enfermedad cardiovascular en pediatría. Hipertensión arterial en niños y adolescentes. Arch Argent Pediatr 2005; 103 (4): 348-357
2. Lobstein T, Baur L, Uauy R. Obesity in children and young children: a crisis in Public Health. Obesity Reviews 2004; Suppl 1: 4-85.
3. Dietz WH, Bellizzi MC. Introduction: the use of body mass index to assess obesity in children. Am J Clin Nutr 1999; 70 (1): 123S-5S.
4. Rosner B, Prineas R, Daniels SR, et al. Blood pressure differences between blacks and whites in relation to body size among US children and adolescents. Am J Epidemiol 2000; 151: 1007-1019.
5. Hirschler V, Delfino AM, Clemente G, et al. ¿Es la circunferencia de cintura un componente del síndrome metabólico en la infancia? Arch Argent Pediatr 2005; 103 (1): 7-13.
6. Daniels SR, Kimball TR, Morrison JA, et al. Effect of lean body mass, fat mass, blood pressure, and sexual maturation on left ventricular mass in children and adolescents. Statistical, biological, and clinical significance. Circulation 1995; 92: 3249-3254.
7. Freedman DS, Kahn HS, Mei Z, et al. Relation of body mass index and waist-to-height ratio to cardiovascular disease risk factors. 2007; 86 (1): 33-40.
8. Hsieh SD, Muto T. The superiority of waist-to-height ratio as an anthro- pometric index to evaluate clustering of coronary risk factors among non-obese men and women. Prev Med 2005; 40: 216-220.
9. Bosy-Westphal A, Geisler C, Onur S, et al. Value of body fat mass vs anthropometric obesity indices in the assessment of metabolic risk fac- tors. Int J Obes (Lond) 2006; 30: 475-483.
10. Gotthelf SJ, Jubany LL. Prevalencia de factores de riesgo cardiovascular en adolescentes de escuelas públicas y privadas de la ciudad de Salta, año 2009. Arch Argent Pediatr 2010; 108 (5): 108(5): 418-426.
11. The Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents. Pediatrics 2004; 114 (2): 555-576.
12. The Seventh Report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. Hypertension 2003; 42: 1206-
13. Sociedad Argentina de Pediatría. Guías para la evaluación del crecimiento. 2a ed. Buenos Aires: SAP, Comité de Crecimiento y Desarrollo. 2001.
14. The WHO Childgrowth Standars. Acceso marzo 2009. Disponible en: www.who.int/childgrwth
15. BMI Classification. Acceso febrero 2009. Disponible en: www.apps.who.int/bmi/index jsp
16. Obesity: preventing and mananging the global epidemic. Report of a WHO Consultation. Geneva. World Health Organization. 2004.
17. Dei-cas Silo A, Dei-cas IJ, Dei-cas PG, et al. Estudio de la presión arterial en adolescentes de 15 años. Su relación con características antropométricas y factores de riesgo de hipertensión arterial. Arch Argent Pediatr 2000; 98 (3): 161-170.
18. Simsolo RB, Romo MM, Rabinovich L, et al. Family history of essential hypertension versus obesity as risk factors for hypertension in adolescents. Am J Hypertens. 1999; 12 (3): 260-263.
19. Poletti OH, Barrios L. Obesidad e hipertensión arterial en escolares de la ciudad de Corrientes, Argentina. .Arch Argent Pediatr 2007; 105 (4): 293-298.
20. Pedrozo WR, Bonneau GA, Castillo Rascon MS, et al. Prevalencia de obesidad y síndrome metabólico en adolescentes de la ciudad de Posadas, Misiones. Rev Argent Endocrinol Metab. 2008; 45 (4): 131-141.
21. Population-Based Prevention of Obesity: The Need for Comprehensive Promotion of Healthful Eating, Physical Activity, and Energy Balance: A Scientific Statement From American Heart Association Council on Epidemiology and Prevention, Interdisciplinary Committee for Prevention. Shiriki K. Kumanyika, Eva Obarzanek, Nicolas Stettler, Ronny Bell, Alison E. Field, Stephen P. Fortmann, Barry A. Franklin, Matthew W. Gillman, Cora E. Lewis, Walker Carlos Poston, II, June Stevens and Yuling Hong. Circulation 2008; 118: 428-464; originally published online Jun 30, 2008; DOI: 10.1161/CIRCULATION AHA.108.189702.
22. Stray-Pedersen M, Helsing RM, Gibbons L, et al. Weight status and hypertension among adolescent girls in Argentina and Norway: Data from the ENNyS and HUNT studies BMC Public Health 2009, 9: 398. Disponible en: http://www.biomedcentral.com/1471-2458/9/398
23. Ostchega Y, Carroll M, Prineas RJ, et al. Trends of Elevated Blood Pressure Among Children and Adolescents: Data From the National Health and Nutrition Examination Survey 1988-2006.Am J Hyperten 2009; 22 (1): 59-67.
24. Despres JP, Lemieux I, Prud'homme D. Treatment of obesity. Need to focus on high risk abdominally obese patients. Br Med J 2001; 322: 716-720.
25. Cox BD, Whichelow MJ. Ratio of waist circumference to height is better predictor of death than body mass index. Br Med J 1996; 313 (7070): 1487.
26. Schwandt P, Bertsch T, Haas GM. Anthropometric screening for silent cardiovascular risk factors in adolescents: The PEP Family Heart Study. Atherosclerosis 2010; 211(2): 667-671.
27. Kelishadi R, Gheiratmand R, Ardalan G, et al on behalf of CASPIAN Study Group. Association of anthropometric indices with cardiovascular disease risk factors among children and adolescents: CASPIAN Study. Int J Cardiol 2007; 117 (3): 340-348.

Publication: June 2012