Decrease in the prevalence of hypertension in Spanish schoolchildren from 2010 to 2017: Cuenca Study

Abstract

Aims

To examine the secular trends in blood pressure measurements and normal or high blood pressure classification among Spanish schoolchildren from 2010 to 2017, to analyze the persistence in the blood pressure category reported in 2017 compared with 2013 in those children born in 2007–08 and to compare in this cohort the prevalence of high blood pressure using both definitions, the 2004 and 2017 guidelines.

Methods and results

The data for the prevalence/trend analysis were obtained from cross-sectional analyses conducted in 2010, 2013, and 2017 of 2709 schoolchildren aged 4–6 and 8–11 years from 22 schools in the province of Cuenca, Spain. The data for the longitudinal analysis were obtained from cross-sectional analyses of measurements gathered in 2013 and 2017 in the same cohort of children (n = 275). The prevalence of normal blood pressure increased by 5.4% in children aged 4–6 years from 2013 to 2017 and by 2.2% in children aged 8–11 from 2010 to 2017. This increase was mainly driven by a decrease in the children classified in any stage of hypertension by 4.2% and 2.3% in each age range, respectively. In the same birth cohort, there was an increase of 7.6% in normal blood pressure prevalence.

Conclusion

The high blood pressure prevalence in Spanish children has clearly decreased over the last decade, but is still important to detect this condition to design specific school-based interventions and the evaluation of children classified as hypertensive who might need medical supervision and treatment.

Graphical Abstract

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Introduction

The prevalence of childhood hypertension (HTN) has rapidly increased worldwide in recent decades. A recent systematic review and meta-analysis revealed global prevalences of 4% for HTN and 9.6% for prehypertension in children under 19 years old.¹ The few studies reporting data about the prevalence of high blood pressure in Spanish schoolchildren estimated it in a range from 1.7% to 8%,^2,3 although there is no consensus about the guidelines used to establish these blood pressure categories among Spanish studies.

In children, HTN was considered a rare disease in the past, but some studies have demonstrated that adult HTN originates in the early period of the lifespan.⁴ In this sense, children with elevated blood pressure are found to be at risk of developing HTN in adulthood,^5–7 leading to a higher risk of cardiovascular events.

Assessing the prevalence of childhood HTN and monitoring its changes over time may be crucial from a public health perspective. Secular trends in blood pressure in children have been reported in different countries, although the findings are not conclusive. While some studies have stated that blood pressure might have decreased in the USA,^8,9 Japan,^10,11 and Korea,¹² other countries, such as China and Thailand, have shown an increase,^13–16 although the general trend seems to be a secular decrease.¹⁷ To our knowledge, no study has analyzed the trend in blood pressure in a Spanish paediatric population.

In 2017, the American Academy of Pediatrics (AAP) recommended a new Clinical Practice Guideline that establishes new blood pressure levels to diagnose elevated blood pressure between children and adolescence.¹⁸ This new guideline introduced some changes in the cut-offs that define abnormal blood pressure and HTN in children, being 2–3 mmHg lower than systolic blood pressure (SBP) and diastolic blood pressure (DBP) levels previously established in 2004 by the National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents.¹⁹ Thus, the use of these new criteria, may have changed the HTN prevalence in children, and it seems relevant to identify the prevalence according to the current recommendations.

Therefore, the objectives of this study were (i) to examine the secular trends in blood pressure measurements and normal or high blood pressure classification among schoolchildren from Cuenca, Spain, from 2010 to 2017 according to the new AAP classification; (ii) to analyze the persistence in the blood pressure category reported in 2017 compared with 2013 in those children born in 2007 and 2008; and (iii) to compare the prevalence of high blood pressure using the AAP classification of 2017 and the previous 2004 National High Blood Pressure Education Program Working Group guidelines in a paediatric cohort from 2013 to 2017.

Methods

Design and study participants

This study includes panel cross-sectional data from different baseline measurements gathered in 2010 (n = 1158), 2013 (n = 626), and 2017 (n = 362 and n = 563) of four cluster-randomized trials conducted in schools of the province of Cuenca, Spain. These ‘MOVI’ trials aimed to evaluate the effectiveness of leisure-time physical activity on the prevention of childhood obesity and cardiometabolic risk. Inclusion criteria for all RCTs required that children in the age range did not have any malformation that prevented them from learning the Spanish language (or Spanish sign language), or any type of physical or mental disorder that parents and/or teachers identified that could prevent the performance of physical activities, or any disease that, according to the criteria of their paediatrician—after analysis of the programme of activities—prevents from their participation in the measurements or the interventions. Supplementary material online, Figure S1 depicts the flow chart of all included studies.

Studies included in the prevalence and trend analysis

4–6 years: In 2013 (MOVI-KIDS study, n = 626) and 2017 (MOVI-da 10! study, n = 362) two similar studies were conducted among schoolchildren in the third grade of preschool (aged 4–6 years) at 10 schools in the province of Cuenca, Spain.^20,21

8–11 years: In 2010 (MOVI-2 study, n = 1158) and 2017 (MOVI-daFit! study, n = 563), similar studies were conducted among schoolchildren attending the 4th and 5th grades (aged 8–11 years) of 20 schools in the province of Cuenca, Spain. The methodology of these studies has been described elsewhere.^22,23

Studies included in the follow-up analysis

The data for the follow-up analysis were obtained from those schoolchildren born in 2007 and 2008 that participated first in the MOVI-KIDS study (basal and endpoints measured in 2013 and 2015) and after, in the MOVI-daFit! study in 2017 (see Supplementary material online, Figure S1). Although it was the same cohort, the schoolchildren that could be measured again in the MOVI-daFit! study was considerably lower (n = 275), mainly because children did not remain in the same school and others because the parents did not sign the consent form when children were 8–11 years. The studies’ methods have been reported elsewhere.^20,23

Ethical and legal aspects

The Clinical Research Ethics Committee of the Virgen de la Luz Hospital in Cuenca approved all studies. The studies were also approved by the Director and Board of Governors (‘Consejo Escolar’) of each school. For data collection, parents gave written consent for their child to participate in the study, and children gave verbal consent when they were asked to collaborate in informative talks held class-by-class. After the data were gathered, the parents were informed by letter of their children’s results.

Study variables

In all the cross-sectional studies, trained and certified nurses collected anthropometric and blood pressure data in each school. Height was assessed as the mean of two measures with a wall-mounted height rod (Seca® 222, Vogel and Halke, Hamburg, Germany) with shoeless children standing straight against the wall so that their spine was vertically aligned with the centre of the height rod. The head was placed with the chin parallel to the floor, and height was measured to the nearest millimetre.

Systolic and diastolic blood pressure, respectively, were measured twice at an interval of 5 min, with the subject resting for at least 5 min before the first measurement, using an OMRON-M5-I automatic tensiometer (Omron Healthcare Europe BV, Hoofddorp, Netherlands). Measurements were taken in a quiet, calm environment, with the child seated with their right arm placed in a semiflexed position at heart level; the most appropriate cuff size was chosen according to recommendations of the National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents.¹⁹ The mean of the two readings was considered for the analysis. The mean arterial pressure (MAP) and the pulse pressure (PP) were calculated as follows: MAP = DBP + [0.333 × (SBP − DBP)], and PP = SBP − DBP.

Statistical analyses

The continuous variables are expressed as the mean [standard deviation (SD)], and the categorical data are expressed as a frequency [95% confidence intervals (CIs)]. Statistical normality was tested using both graphical (normal probability plot) and statistical (Kolmogorov–Smirnov test) procedures using the statistical software package IBM SPSS Statistics 24.0 (SPSS Inc., Chicago, IL, USA). All variables included in the analysis had a normal distribution.

According to the AAP guidelines, blood pressure values were established according to the percentile for sex, age, and height in children younger than 13 years as follows: normal blood pressure (<90th percentile), elevated blood pressure [≥90th percentile to <95th percentile or 120/80 mmHg to <95th percentile (whichever is lower)], HTN stage 1 [≥95th percentile to <95th percentile + 12 mmHg, or 130/80 to 139/89 mmHg (whichever is lower)], and HTN Stage 2 [≥95th percentile + 12 mmHg, or ≥140/90 mmHg (whichever is lower)].¹⁸

Depending on the analysis, elevated blood pressure, HTN Stage 1 and HTN Stage 2 categories were grouped into a single category.

The prevalence and 95% CI were calculated for each blood pressure category in all MOVI included studies (2010, 2013, and both of 2017). We calculated the differences in proportion distributions of each blood pressure category using χ  ² test and mean differences of each blood pressure measurement using Student’s t-test from 2010 to 2017 by age group and sex using EPIDAT 4.2 software.

The 275 schoolchildren from the birth cohort born between 2007 and 2008 who participated in both measurements were included in the analysis of categorization in the same blood pressure category between 2013 and 2017, which was analyzed by calculating the percentage observed agreement based on a contingency table. Finally, the relative risk of remaining in the same blood pressure category in 2017 (normal and any stage of HTN) among schoolchildren who were in that category in 2013 was calculated.

To compare the blood pressure status of the schoolchildren with the previous classification in 2004, categories of high blood pressure in the schoolchildren were also established according to the percentile for sex, age, and height published in 2004.¹⁹ Differences in proportion distributions between 2004 and 2017 classifications after 4 years of follow-up were calculated using the χ  ² test with EPIDAT 4.2 software.

Results

The response rate of schools at baseline was 67.0% in 2010, 65.9% in 2013, and 66.9% in 2017. There was a similar proportion of girls and boys in each study (∼50%), with no statistically significant differences in age by sex.

Trends in blood pressure measurements and prevalence of hypertension in children aged 4–6 and 8–11 years from 2010 to 2017

In children aged 4–6 years, the prevalence in the normal category significantly increased from 85.1% (95% CI: 82.1–87.8) in 2013 to 90.5% (95% CI: 87.0–93.4) in 2017, reducing the prevalence in the elevated blood pressure category by 1.2% (95% CI: −4.4 to 2.0), reducing the prevalence in the HTN Stages 1 and 2 categories by 4.2% (95% CI: −6.9 to −1.4).

In children aged 8–11 years, the prevalence of normal blood pressure from 2010 to 2017 increased from 89.1% (95% CI: 87.2–90.9) to 91.3% (95% CI: 88.5–93.3) (P = 0.168). Differences were only found when both categories of HTN (Stages 1 and 2) were analyzed together, with a reduction in the prevalence of 2.3% (95% CI: −4.1 to −0.3) (P < 0.05).

Among the blood pressure variables, there was a marked reduction in PP in 2017 in both comparisons: in children aged 4–6, there was a decrease of 8.7 mmHg (95% CI: −9.6 to −7.8) (P < 0.001) and a decrease of 3.6 mmHg (95% CI: −4.3 to −2.9) (P < 0.001) in children aged 8–11 years. These results are consistent with the reduction in SBP and the increase in DBP in the 2017 clusters compared with the 2013 data in preschool children and older children in 2010 (Table 1).

Data according to sex are shown in Supplementary material online, Table S1 (girls) and Supplementary material online, Table S2 (boys). In girls aged 4–6 years, the normal blood pressure prevalence increased by 6.1% (95% CI: 0.1–12.0). In girls aged 8–11 years, the prevalence of HTN Stages 1 and 2 decreased, but there was an increase in girls classified as having elevated blood pressure [from 5.1% (95% CI: 3.4–7.3) in 2010 to 7.5% (95% CI: 4.8–11.2) in 2017, P = 0.153] (see Supplementary material online, Table S1).

In boys aged 4–6 years, the prevalence of normal blood pressure was slightly higher in 2017 than in 2013 [91.0% (95% CI: 85.7–94.7) vs. 86.2% (95% CI: 81.9–89.7), P = 0.115], which was mainly driven by a decrease in the prevalence of elevated blood pressure and HTN Stage 2. In the older sample (aged 8–11 years), boys had a significantly higher prevalence of normal blood pressure [4.8% (95% CI: 0.7–8.9), P = 0.036] in 2017 than in 2010.

Trends in blood pressure measurements and prevalence of hypertension during 4 years of follow-up (from 2013 to 2017) in the 2007–09 birth cohort

In 2013, 1190 schoolchildren were invited to participate in the baseline measurements of MOVI-KIDS, and 653 (54.8%) agreed to participate; of these same children, after 4 years of follow-up, anthropometric data were obtained from 275 schoolchildren (49.8% boys). The low follow-up rate was mainly due to changes in school or residence of schoolchildren or absence (due to illness or travel) of children in 2015 and 2017. The age of the participants at the beginning of the follow-up ranged between 57 and 81 months (mean = 70.87, SD = 6.78), and 18.8% lived in the capital (Cuenca) (Table 2).

Among these 275 schoolchildren, the evolution over 4 years showed an important decrease in HTN levels from 2013 to 2017. Specifically, the prevalence of HTN Stage 1 and Stage 2 decreased from 2013 to 2017 by 3.3% (95% CI: −5.6 to −0.9, P = 0.006) and 2.2% (95% CI: −4.2 to −0.2, P = 0.033), respectively. The normal blood pressure prevalence increased from 86.2% (95% CI: 71.5–90.0) in 2013 to 93.8% (95% CI: 90.3–96.4) in 2017. This significant increase was driven by a significant increase in DBP mean values [mean difference from 2013 to 2017: −4.9 (−5.9 to −3.8), P < 0.001].

Prevalence of categorization in the same blood pressure categories in the 2007–08 birth cohort

Table 3 shows the prevalence of categorization in the same blood pressure categories between 2013 and 2017 in the 2007–09 birth cohort. A total of 85.1% of the schoolchildren remained in the same blood pressure category after 4 years.

Specifically, the relative risk for persistence in the normal blood pressure category in 2017 was 1.32 (95% CI: 1.09–1.59). In addition, taking together the HTN categories (elevated blood pressure, HTN Stage 1 and HTN Stage 2), the relative risk for persisting in 2017 in any of these categories was 8.91 (95% CI: 3.61–21.98).

Comparison of the elevated blood pressure and hypertension prevalence between the 2004 Fourth Report guidelines and the new 2017 guidelines of the AAP in the 2007–09 birth cohort

Finally, in the same 2007–09 birth cohort, we compared the prevalence of blood pressure categories according to the National High Blood Pressure Education Program Working Group of 2004 and the Guidelines for Screening and Management of High Blood Pressure in Children and Adolescents of the AAP of 2017 in Supplementary material online, Figure S2.

In general, the prevalence of elevated blood pressure, HTN Stage 1, and HTN Stage 2 according to the AAP classification was higher, but not significantly, than in 2004. For example, for the HTN Stage 2 classification, the prevalences in 2013, 2015, and 2017 were 1.1%, 2.5%, and 0.4%, respectively, according to the 2004 classification, increasing to 2.5%, 3.3%, and remaining at 0.4%, respectively, according to the AAP 2017 guidelines (P > 0.05).

Discussion

This study examines the prevalence of high blood pressure in children aged 4–11 years from 2010 to 2017 from the province of Cuenca, Spain, of the trends in using the new AAP classification. Our results clearly show a declining trend in the prevalence of high blood pressure among children in Spain. Moreover, children diagnosed with elevated blood pressure had a relative risk of 8.91 for persisting in the same category 4 years later. Finally, we can affirm that the use of the 2017 Guidelines for Screening and Management of High Blood Pressure in Children and Adolescents slightly increased the prevalence of elevated blood pressure and HTN compared with the use of the guidelines of 2004, although these changes were not statistically significant. Therefore, the use of these new guidelines may offer a realistic view of the extension of elevated blood pressure conditions in Spanish schoolchildren.

Our results show that the prevalence of Spanish children in the elevated blood pressure categories (elevated blood pressure and HTN Stages 1 and 2) has decreased from 2010 to 2017 in children aged 8–11 and from 2013 to 2017 in preschoolers aged 4–6.

These results are in line with other studies conducted in the USA.^8,9,24,25 Al Kibria et al.,⁸ using the National Health and Nutrition Examination Survey (NHANES) data from the USA, found that the prevalence of high blood pressure in children aged 8–12 decreased from 13.9% (95% CI: 10.8–17.8) in 2005–08 to 10.5% (95% CI: 8.9–12.4) in 2013–16 according to the 2017 AAP classification. Similar findings were reported by Overwyk et al.²⁴ from 2003–04 to 2015–16 based on the NHANES survey, where the prevalence of elevated blood pressure and HTN decreased from 16.2% (1.8) to 13.3% (1.2) in the population aged 8–12 years.

This downward trend in high blood pressure prevalence has not been detected in some Asian countries, such as China or Korea. While one study reported a stabilization in the prevalence of high blood pressure among Chinese participants aged 7–17 years,¹⁴ others found a significant increase in recent years.^26,27 In Korea, the prevalence of HTN increased from 2013 to 2015 in the paediatric population and was especially high among obese participants.¹³

Nonetheless, a systematic review published in 2016 of the secular trends in blood pressure in children concluded that blood pressure prevalence decreased in most of the included studies, while the prevalence of obesity and overweight did not, implying that other factors might mitigate the effect of overweight on blood pressure in children and adolescents.¹⁷

A recent meta-analysis showed that the global prevalence of HTN increased from 2000 to 2010 and 2015, and the increasing rates were similar across the whole included age range (6–19 years old). Although more than half of the studies collected blood pressure data with a mercury sphygmomanometer, they concluded that childhood HTN had an upward trend during the past two decades that may persist in the future.²⁸

This hypothesis was not supported in our sample, where the 4-year follow-up birth cohort (2007–09) showed a significant decrease in the prevalence of high blood pressure categories. The best possible explanation of the decrease in blood pressure in our population could be linked to the stabilization of overweight and obesity from 1992 to 2017,²⁹ possibly caused by the positive effect of intervention programmes focused on promoting healthy habits among children.^{20,21,23,30,31}

Remarkably, a significant downward trend was observed not only in blood pressure but also in PP in both paediatric cohorts due to the reduction in SBP and the increase in DBP in the 2017 cluster. Pulse pressure is determined by arterial diameter, flow volume, and aortic tissue stiffness,³² so a decreased SBP leads to lower flow rates and results in unnecessary enlargement of the diameter of large arteries, preserving normal arterial stiffness.

In fact, the evaluation of vascular function and morphological parameters in overweight/obese children has demonstrated that endothelial dysfunction, enlargement of the abdominal aorta, and elevated haemostatic biomarkers like high-molecular weight adiponectin appear from the early stages of life.^33,34 These parameters in children with elevated body mass index highlight the need to jointly evaluate childhood obesity with vascular function to reduce the risk of future HTN and prevent cardiovascular disease.³⁵

In the birth cohort (2007–09), the probability of remaining in the same blood pressure category from 2013 to 2017 was 85.1% (relative risk 8.91). This result shows that children diagnosed with HTN at an early age have a higher risk of remaining in the same category years later, which may suggest the importance of designing specific strategies for this group, including the promotion of healthy habits (physical activity and an adequate dietary pattern) and medication,³⁶ if necessary, to control this condition from the moment it has been diagnosed.

Since the publication of the new AAP guidelines in 2017 for the screening of high blood pressure in the paediatric population, some research³⁷ has been conducted in order to determine the differences in blood pressure prevalence using the 2004 Fourth Report guidelines and the new ones, because the latter established a reclassification of blood pressure categories using new tables that excluded children who were overweight and obese.¹⁸ Our findings were in line with these previous studies suggesting that the prevalence of elevated blood pressure, HTN Stage 1, and HTN Stage 2 using the 2017 guidelines was higher than that in 2004,³⁸ although these changes were not statistically significant. This result may be explained due to the age characteristic of our sample (children ≤11 years old), because the APP guidelines have introduced more significant changes in the definition of HTN for adolescents ≥13 years of age than in children <13 years.³⁹ Most of the published studies have reported an increase in the prevalence of HTN when the AAP guidelines had been used, but all of them have considered a wider age range that included adolescents, for example, healthy children aged 5–18 years,⁴⁰ or children aged 10–17 years.^41,42 Yang et al.⁴³ found that children who were reclassified in a higher blood pressure category had an adverse lipid profile and high fasting glucose and were more likely to be overweight and obese. In the same line, Du et al. ⁴⁴ found that 19% of children identified as hypertensive in childhood using APP Guidelines developed left ventricular hypertrophy in adulthood in comparison with the 12% identified by the Fourth Report.¹⁹

Thus, the use of the 2017 AAP guideline is generally recommended because due to a greater sensitivity, its application may more accurately detect elevated blood pressure in children, which might help to identify in advance those people who are most at risk of developing premature cardiovascular disease in their adulthood. Consequently, the increased cardiovascular risk for these children might be limited if the preventive strategies are designed from an early stage.¹⁷

Overall, if the trend in blood pressure in the children studied continues to decrease in the following years, it may suggest a lower risk of developing cardiovascular diseases and, therefore, a lower mortality risk for these birth cohorts. However, there is not enough evidence about the effectiveness of the treatment of children and adolescents with high blood pressure (lifestyle and/or pharmacologic) for improving the blood pressure or other intermediate variables are long term.⁴⁵

This study presents some limitations that should be noted. First, the cross-sectional design of the baseline measurements from four cluster-randomized trials prevents us from making cause-effect inferences. Second, the use of the AAP criteria to define elevated blood pressure in children does not allow comparability with other Spanish studies that analyzed high blood pressure in the paediatric population. Finally, we only analyzed a limited population of children aged 4–11 from Cuenca, Spain; extrapolation of the results to other age groups and Spanish geographic areas may not be accurate and should be done with prudence.

Conclusion

In conclusion, the childhood elevated blood pressure and HTN prevalence in Spain have clearly decreased over the last decade, showing a similar trend as those recorded in other countries. The causes of this downward trend remain unknown, so more research is necessary to understand the factors that may be implicated in this phenomenon. However, despite this tendency, more children have been categorized as having elevated blood pressure or HTN using the new AAP criteria and there is a high relative risk of 8.91 of remaining in the same blood pressure category across the years. Thus, a better detection of this condition may allow the design of specific school-based interventions for both prevention and focused on persistent hypertensive children, and for the evaluation of newly children classified as hypertensive who might need medical supervision and treatment.

Supplementary material

Supplementary material is available at European Journal of Cardiovascular Nursing online.

Acknowledgments

We thank the schools, families, and children for their enthusiastic participation in the study.

Funding

This study was funded mainly by the Junta de Comunidades de Castilla-La Mancha - Consejería de Educación y Ciencia (PII1I09-0259-9898 and POII10-0208-5325). Additional funding was obtained from the Carlos III Health Institute (FIS PI08/1297, PI12/02400, PI12/00761, and PI19/01919) and from the Ministerio de Economía y Competitividad - Research Network on Preventative Activities and Health Promotion (Ref. RD06/0018/0038 and Ref. RD12/0005/0009).

Data availability

The data that support the findings of this study are available from the corresponding author, A.D.-F. upon reasonable request.

Author agreement: Substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data: N.M.-E., M.S.-M., A.D.-F., and V.M.-V. Drafting the article or revising it critically for important intellectual content: A.I.C.-C., N.M.-E., A.D.-F., M.G.-M., A.D.-F., and V.M.-V. Final approval of the version to be published: all authors.

References

Author notes