An approach of hypertension prevalence in a sample of 5381 Portuguese children and adolescents. The AVELEIRA registry. “Hypertension in Children”

Abstract

Introduction. The distribution of blood pressure (BP) in children and adolescents remains relatively unknown. Thus, it is imperative to ascertain BP distribution at a young age, which constitutes the main objective of this registry. Methods. Cross-sectional assessment of BP in 5381 Portuguese children and adolescents, mean age 12.50±3.23 years (4–18 years), body mass index (BMI) 19.65±4.00 kg/m² (9.37–60.30 kg/m²), mostly male (4519), mean age 12.70±3.16 years, and with 862 females, mean age 11.44±3.34 years. BP and heart rate were measured three times after a 10-min resting period, with a validated automatic blood pressure monitor (OMRON 705IT) and an appropriately sized cuff over the brachial artery. About 30% of the youngsters were amateur registered athletes and 70% were beginning their sportive activity at the time of evaluation. Results. BP distribution was 12.8% stage 1 hypertension, 21.6% high-normal, and 65.6% normal (similar between genders). Registered athletes and subjects beginning their sports activity revealed different hypertension prevalence (9.8% vs 14.3%, respectively; p < 0.0001). Overweight was found in 7.8%. Hypertension and high-normal BP increased with increasing BMI. Body weight classification was independently associated with hypertension and high-normal BP. Registered sportive practice was independently associated with a reduction in hypertension prevalence. Conclusions. The proportion of children with BP above the 90th percentile was high, with an overall prevalence of hypertension of 12.8%, independent of gender and related to overweight. The implications of these observations are even more important when we consider the epidemiology of hypertension in Portugal and its link with stroke as the leading cause of death and disability.

Key Words::

• Hypertension
• blood pressure
• pediatrics
• prevalence
• overweight

Introduction

Cardiovascular disease is the leading cause of death in industrialized countries (1). In Portugal, it is a major public health problem that is closely linked to the high prevalence of hypertension (2,3). Recent studies have reported a prevalence of 42.1% in Portugal, the patient very often being unaware of the condition (1). In addition to these worrying figures, the percentage of patients with treated but uncontrolled hypertension is high, with only 11.2% having their blood pressure (BP) controlled (3).

This situation is relatively well documented in the adult population, but information on children and adolescents is scarce, which reflects the view of hypertension as a disease of adulthood. However, it is essential to determine the blood pressure distribution in children and adolescents, given the direct link between blood pressure at these ages and in adulthood (4). Furthermore, the fact that BP levels have tended to rise in children and adolescents in recent years adds weight to the existing evidence of the seriousness of public health problems caused by hypertension (5). In this context, knowledge of the physiological and biological processes taking place during maturation is essential to understand the etiopathogenesis of hypertension and of other risk factors associated with major cardiovascular events (6,7). This is crucial for the implementation of public health measures designed to improve cardiovascular prevention. The aim of the present study was to increase our knowledge of blood pressure distribution in children and adolescents, in particular the prevalence of hypertension.

Methods

Population sample

The sample was composed of 5381 children and adolescents, with a mean age 12.50±3.23 years (ranging from 4 to 18 years), mostly male, referred for sports medicine consultations in a clinic in the Central region of mainland Portugal. Table I summarizes the main characteristics of the sample. Overweight was found in 7.8% of the subjects (6% in females and 8.25% in males), 14.4% were at risk of overweight and 77.8% had normal weight.

Table I. Demographic characteristics (n=5381).

Age (years)	12.5±3.23 (4–18)
Sex
Male	84%
Female	16%
BMI classification
Healthy weight (5th–<85th percentile)	77.8%
At risk of overweight (85th–<95th percentile)	14.4%
Overweight (≥95th percentile)	7.8%
SBP (mmHg)	115.43 ± 10.66
DBP (mmHg)	66.87 ± 8.29
HR (mmHg)	71.42 ± 13.36

BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; HR, heart rate.

The sample comprised a subgroup of 1805 registered athletes, with a mean of 1.01±2.01 years of sports activity and a mean 5.86±2.78 training hours/ week, mostly in soccer or gymnastics. The remaining 3576 children were just beginning to participate in organized sports at the time of evaluation. Table II summarizes the main characteristics of both subgroups. Differences were found mainly in hours of weekly training and in years of sports activity, which were null for the registering children. Registered athletes were older, explaining the differences found in body mass index (BMI), blood pressure and heart rate, which disappeared after age adjustment was performed for the comparative analysis.

Table II. Demographic characteristics stratified by sportive practice.

	Non-athletes	Registered athletes	p
n	3576	1805*	<0.05
Age (years)	11.82 ± 3.17	13.85 ± 2.89	<0.05
Sex	86.6%	78.8%	ns
Male
Female	13.4%	21.2%	ns
BMI classification
Healthy weight (5th–<85th percentile)	75.4%	82.5%	<0.05
At risk of overweight (85th–<95th percentile)	15.6%	12.0%	ns
Overweight (≥95th percentile)	9.0%	5.5%	<0.05
BMI (kg/m^2)	19.34 ± 4.19	20.29 ± 3.64	<0.05
Registered sports practice (years)	–	1.01 ± 2.01	–
Training load (h/week)	–	5.86 ± 2.78	–
SBP (mmHg)	114.45 ± 10.83	117.35 ± 10.05	<0.05
DBP (mmHg)	66.95 ± 8.40	66.71 ± 8.04	ns
HR (beats/min)	72.57 ± 13.01	66.71 ± 8.04	<0.05

*p < 0.05; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; HR, heart rate.

Overweight was more prevalent in the non-athletes children (9.0% vs 5.5% in the registered athletes, p< 0.05).

Study procedure

BP measurement was performed in all subjects by experienced operators with a validated automatic blood pressure monitor (OMRON 705IT) and with an appropriately sized cuff, following the recommendations of the American Academy of Pediatrics (8). BP was measured initially in both arms, and was then measured three times in the arm with the higher value, together with heart rate, on a single occasion, after a 10-min resting period and with a 2-min interval between measurements. Whenever BP values were high, confirmation was made with a standard mercury sphygmomanometer. The mean of the values obtained was used in the analysis. BP was classified according to the criteria of the American Academy of Pediatrics (8), with hypertension defined as systolic (SBP) and/or diastolic (DBP) BP above the 95th percentile for gender, age and height. Prehypertension, or high-normal BP, was defined as SBP and/or DBP between the 90th and the 95th percentiles. Waist, hip, weight and height were also measured, and BMI was calculated by dividing weight in kilograms by the square of height in meters. BMI was then classified by its distribution by percentiles for gender and age, based on the criteria of the US Centers for Disease Control and Prevention, defining obesity as BMI above the 95th percentile and overweight as BMI between the 85th and 95th percentiles (9).

Subjects’ weight was measured with a calibrated digital scale and height with a stadiometer graduated with an accuracy of 0.1 cm.

All participants also filled out a questionnaire on social, demographic and behavioral characteristics and personal and family history of disease. This information was not analyzed in this phase of the registry.

All participants’ parents gave informed consent for the use of their data for research purposes.

Statistical analysis

Data on the population sample were analyzed using SPSS for Windows, version 16.0. The distribution of the variables was tested for normality using the Kolmogorov–Smirnov test and for homogeneity of variance with the Levene test. Continuous variables were analyzed descriptively, and means, standard deviation, standard error of the mean, median and range of variation were estimated. The chi-square test was used to analyze the association between categorical variables. The Student's t-test or the Mann–Whitney U test were used to compare two groups, depending on whether the variable under consideration was parametric or non-parametric. Comparison between more than two groups was by analysis of variance (ANOVA) or the Kruskal–Wallis H test as appropriate. Bivariate correlations were also analyzed (Pearson's r) when necessary. Logistic regression analysis was performed to identify the main determinants of hypertension. A value of p≤ 0.05 was taken to indicate statistical significance for a 95% confidence interval.

Results

Overall prevalence of hypertension in this sample of children and adolescents was 12.8% (all stage 1 hypertension), and 21.6% were classified as having high-normal BP, with 65.6% having normal BP. The hypertension prevalence was similar in males and females (12.8% in both), but males presented higher prevalence of high-normal BP (22.5% vs 17.3% in females; p<0.05) and females showed a greater distribution in the normal category (69.9% female vs 64.8% male; p<0.05). Mean BP levels were significantly different, with boys having mean BP values of 115.93±10.64 and 67.00±8.37 mmHg and girls having 112.77±10.37 and 66.12±7.81 mmHg (SBP and DBP, respectively; p<0.05). Mean heart rate was significantly lower in boys compared with girls (71.00±13.35 and 73.64±13.16 beats/min, respectively; p< 0.05).

Considering the BP distribution in non-athletes and registered athletes, significant differences were observed. Hypertension was seen in 14.3% of the non-athletes against 9.8% of the registered-athletes (p<0.05). High-normal BP was also more prevalent in the non-athletes subgroup (22.90% against 19.20% in the registered athletes subgroup, p<0.05).

The relation between BP and anthropometric characteristics was also assessed in view of the well-known link between hypertension and obesity. Simple linear correlation analysis showed statistically significant positive correlations between SBP and age (r=0.50), BMI (r=0.32), hip (r=0.48) and waist (r=0.47). The relation of DBP with the same variables was also significant, although less strongly, with linear correlation coefficients of <0.3 age and BMI and r=0.58 for waist and hip. The overall prevalence of overweight was 7.8% (6.0% and 8.2% in girls and boys, respectively, p< 0.05), being 9.0% in the non-athletes and 5.5% in the registered athletes.

Stratified prevalence by sportive practice and overweight status is shown in Table III. An increase in arterial hypertension prevalence with overweight is observed in both groups, but with greater expression in the non-athletes subgroup. Logistic regression analysis (Table IV) further emphasizes this relation, with overweight appearing independently associated with hypertension (OR=1.94, 95% CI 1.50–2.50) and with normal-high BP classification (OR=1.60, 95% CI 1.26–2.03). A linear trend of increase in hypertension prevalence with BMI classification was clearly depicted. The absence of sportive practice was also independently associated with a 47% increase in the risk of being diagnosed with arterial hypertension (OR=1.47, 95% CI 1.22–1.76), and a 30% increase in the risk of having normal-high BP (OR=1.30, 95% CI 1.12–1.50). Male gender was only independently associated with high-normal BP classification (OR=1.36, 95% CI 1.12–1.65).

Table III. Prevalence of hypertension by sportive practice and weight status.

	Normotension	Normal-high BP	Hypertension
Non-athletes (n = 3567)
Healthy (n = 2690)	65.1%	22.2%	12.8%
At risk (n = 556)	59.0%	24.5%	16.5%
Overweight (n = 321)	51.1%	26.2%	22.7%
Registered athletes (n = 1793)
Healthy (n = 1479)	73.1%	18.2%	8.7%
At risk (n = 215)	62.8%	20.9%	16.3%
Overweight (n = 99)	58.6%	28.3%	13.1%

BP, blood pressure.

Table IV. Crude and adjusted odds ratios for elevated vs normal blood pressure.

	Normal-high BP		Hypertension
	Crude OR	Adjusted OR	Crude OR	Adjusted OR
Weight
Healthy	1.0 ref	1.0 ref	1.0 ref	1.0 ref
At risk	1.28 (1.06–1.54)	1.25 (1.03–1.50)	1.54 (1.25–1.91)	1.50 (1.21–1.86)
Overweight	1.65 (1.30–2.10)	1.60 (1.26–2.03)	2.01 (1.56–2.60)	1.94 (1.50–2.50)
Sex
Female	1.0 ref	1.0 ref	1.0 ref	1.0 ref
Male	1.40 (1.16–1.70)	1.36 (1.12–1.65)	1.00 (0.81–1.24)	0.93 (0.75–1.16)
Registered athlete
Yes	1.0 ref	1.0 ref	1.0 ref	1.0 ref
No	1.35 (1.17–1.56)	1.30 (1.12–1.50)	1.53 (1.27–1.83)	1.47 (1.22–1.76)

Adjusted OR, odds ratio adjusted for age and gender; BP, blood pressure; OR, odds ratio; ref, referential.

Discussion and conclusions

The prevalence of hypertension, traditionally viewed as a disease of adulthood, has been increasingly studied in children and adolescents, mainly because high blood pressure in childhood is related to factors associated with hypertension in adults (4–7). At the same time, the concept of the cardiovascular continuum means that preventive measures should be adopted as soon as possible, and awareness of alterations at young ages can prompt early preventive strategies with positive long-term benefit. In Portugal, the burden of hypertension in adults is well known. Estimated prevalence is 42.1%, with over half of hypertensives unaware of the fact and only 11.2% of treated hypertensives having their blood pressure controlled (3). These figures are a stark illustration of the gravity of the public health problems associated with the pathology in adults. However, there are considerable gaps in our knowledge of the situation concerning younger age groups. In fact, the available data regarding the prevalence of hypertension in this specific context is quite inconsistent, as it was well stressed in the recently published guidelines of the European Society of Hypertension (10). There have been few studies on hypertension in children and adolescents in Portugal, and international studies have shown widely differing prevalences. O’Quin et al. (11) studied 5537 adolescents aged between 14 and 19 in the American city of Tulsa and estimated the prevalence of hypertension at 6%. Another study, by Genovesi et al. (12), of 2416 children between the ages of 6 and 11 in the Italian province of Milan, documented a prevalence of 4.2%, significantly higher in girls (5.4%) than in boys (3.1%). Prevalences of around 1% were found in a large series of adolescents (n=19,542; ages between 10 and 15) in the US state of Minnesota (13). Other studies have reported prevalences ranging from 10.6% (14) to 4.5% (15).

In the present study, the prevalence of hypertension was 12.8%, with similar figures in boys and girls (12.8% in both). The prevalence found in the study is significant, slightly higher than in the international studies referred to above (11–15), all the more so given the characteristics of the sample, which consisted of extremely healthy subjects whose levels of physical activity would clearly be above average and with overall obesity levels below those estimated for the general population (16,17). This suggests that the real prevalence of hypertension in the young may be even higher than in the present study. In fact, a stratified analysis of prevalence in the two subgroups (registered athletes and non-athletes) revealed a significantly larger proportion of hypertensive children in the non-athletes (14.3%) than in the athletes (9.8%), pointing out that the true prevalence of hypertension in the general population could be even greater. This is in line with a relatively recent study that documented a prevalence of hypertension around 22% in a sample of 2023 13-year-old Portuguese children enrolled at public and private schools in Porto, by Ramos et al. (18). This is even more worrying when considering the results of other studies, such as that by Macedo et al. (19), which assessed the prevalence of hypertension in 889 children aged 5–18 in northern Portugal and its association with obesity. The estimated prevalence of hypertension was 5.2%, around one third the overall figures in our study. Bearing in mind the decade between the two studies, we can cautiously suggest that the pathology is increasing in these age groups. The link between hypertension and obesity in Macedo et al.'s study (19), a similar tendency for which was found in our study, highlights the importance of behavioral and environmental factors in development of the disease and its distribution. In line with these arguments, our data further revealed an independent relationship of sports practice with hypertension, being associated with a reduction in its prevalence.

In view of the implications for the future, it is imperative to implement preventive strategies at these ages, with a strong emphasis on health education in general and on cardiovascular prevention in particular. We should stress the importance of reducing body weight and implementing regular sportive practice early in life.

The limitations of the present study arise from the specific characteristics of the sample and context of BP evaluation. It has an essentially regional nature, although it comprises coastal and interior populations, a situation that makes credible a rigorous approach to the national reality. Caution should therefore be exercised in interpreting its results. The fact that only children particularly interested in sport were assessed limits extrapolation of the results to these age groups in general. It should also be noted that blood pressure was assessed in one single moment, as in many other reference studies on prevalence (3,19). On the other hand, the size of the study population is considerable, and unusually large for Portugal, which gives the results added impact. Notwithstanding the study's limitations, the implications of its results are of sufficient significance to warrant further studies, representative and well designed, in order to determine the real prevalence of hypertension in children and adolescents in Portugal, on the assumption that the epidemiological data may indicate the real possibility of a clinically important situation. At the same time, the results presented here should, in our opinion, alert health authorities to the need for measures to promote cardiovascular health in these age groups, which would undoubtedly lead to a wide range of benefits in the long term.

Conflicts of interest None.