Normative Values of Height, Bodyweight and Body Mass Index of 12–17 Years Population from Extremadura (Spain)

Simple Summary Growth charts constitute an essential tool for monitoring adolescents’ development. The percentile growth charts currently used are based on Basque Country population. Considering socioeconomic differences between Spanish regions, growth chart data could be inappropriate. Thus, a descriptive cross-sectional study with 4130 adolescents was conducted to describe the percentile distribution of adolescents from Extremadura and compares these percentiles with those used as reference. Bodyweight, height and BMI of Extremadura adolescents differ from the reference values currently applied. Thus, the need to use new indicators should be considered, adapted to the physical and anthropometric reality of children and young people to avoid the possible normalization of situations of thinness, overweight or obesity. Abstract Background: Growth charts constitute an essential tool for monitoring adolescents’ development. In Extremadura, the percentile growth charts by Faustino Orbegozo Foundation are used. However, they are based on Basque Country population data. Considering socioeconomic differences between Spanish regions, growth chart data could not be appropriate. Aims: to describe the percentile distribution of adolescents from Extremadura and compare these percentiles with those proposed by the Faustino Orbegozo Eizaguirre Foundation that are currently applied in the Extremadura Health Service. Methods: A descriptive cross-sectional study was conducted. A total of 4130 adolescents (12–17 years) participated into the study. Bodyweight and height were assessed. Results: Significant differences were found comparing real measured values with commonly used reference tables for bodyweight at all ages between 12 and 13 years and at 14 years in both gender (p < 0.05). Differences were also found in boys at 15, 16.5 and 17 years (p < 0.05). Regarding height, significant differences were reported at 12, 13, 14.5, 15, 16.5 and 17 years old (p < 0.05) in males; while females’ results only revealed differences at 12, 12.5, 14.5 and 15.5 years (p < 0.05). BMI outcomes showed differences in both gender at 12, 12.5, 13, 14 and 15 years old (p < 0.05). Differences were also found at 16 and 14.5 years for boys and girls, respectively (p < 0.05). Conclusion: Bodyweight, height and BMI of adolescents from Extremadura differ of the reference values currently applied. Hence, this study’s outcomes suggest the need to use new indicators, adapted to the physical and anthropometric reality of children and young people to avoid the possible normalisation of situations of thinness, overweight or obesity.


Introduction
Intergenerational changes in bodyweight, height, and body mass index (BMI) have been exposed in different long-term trend studies on physical characteristics of children and

Ethics Approval
A favourable report was obtained from the Bioethics Committee of the University of Extremadura, considering that it complied with all the relevant regulations (reference code 11/2006).

Participants
Thirty-nine secondary schools from Extremadura were contacted to participate in this study. A total of 4130 adolescents (2128 males and 2002 females), aged between 12 and 17 years, participated into this study. Participants had to meet the following eligibility criteria to be included in this project: (1) age: 12 to 17 years; (2) registered and/or resident in the autonomous community of Extremadura; (3) authorised by parents or legal guardians; (5) acceptance of the adolescents to participate in the study.

Sample Size
To provide estimates with a certain degree of reliability of the survey at Autonomous Community level, a sample of 4130 individuals between 12 and 17 years of age has been selected. Based on data from the National Institute of Statistics of Spain (www.ine.es, accessed on 16 June 2021) [22], the population for this age bracket is 74,239 in Extremadura (51.3% males, 48.7% females).
Sections are made within each stratum with probability proportional to its size. Proportional allocation between strata (health areas) was used. Within each stratum, the size of each sub-stratum (rural or urban area) was used. The type of sampling was proportional in age and gender quotas, randomly selected within the educational centre of the determined populations.

Procedures and Measures
Data collection was carried out in their respective educational institutions by trained and standardised health personnel. The measurements were performed under standardized conditions, following the protocol established in the Data Collection Procedure Manual, developed specifically for Childhood Obesity Surveillance Initiative (COSI) [23]. For measuring bodyweight and height, participants were asked to remove their shoes and socks and any heavy clothes (coats, sweaters, jackets, etc.) or accessory (pockets, belts). Height was measured with a stadiometer (Tanita Tantois, Tanita Corporation, Tokyo, Japan) placed on a vertical surface with the measurement scale perpendicular to the ground. It was measured on a standing position, with shoulders balanced and arms relaxed along the body. The outcome was taken in cm, to the nearest mm. Bodyweight was evaluated using a bioimpedancemeter (Tanita MC-780 MA, Tanita Corporation, Tokyo, Japan) and was recorded in kg, up to the nearest 100 g. BMI was calculated using the formula: bodyweight (kg) divided by height squared (m 2 ).

Statistical Analyses
All information collected was tabulated in a database specifically designed for this purpose. Statistical analyses were carried out using IBM SPSS Statistics software, version 25. Descriptive statistics were performed for all parameters, including as measures of central tendency the mean and standard deviation (SD) for the dispersion of quantitative variables and percentiles (2,3,10,15,20,25,50,50,75,80,85,90, 97 and 98) as measures of position.
Normality and homogeneity of data was checked applying Kolmogorov-Smirnov and Levene's test, respectively. Then, differences between the Extremadura data and the reference study by Faustino Orbegozo Eizaguirre (currently used by the Extremadura Health Service) were examined by applying an Independent samples T-Test adjusted by age and gender. Alpha level was set at p ≤ 0.05. Hedge's g effect size (95% confidence interval) was calculated to determine the magnitude of between reference methods comparisons. Effect size thresholds were interpreted, as follow [24]: >0.2, small; >0.5, moderate; >0.8, large. Table 1 shows participant's characteristics of bodyweight, height and BMI stratified by gender and age. The number of participants assessed for each group is also indicated. Results indicates that boys experience an increase in bodyweight (12.3 kg) and height (10.2 cm) between 13.5 and 15 years old, stabilizing both in posterior ages. With respect to BMI, there is a progressive increase from 12 to 17 years, obtaining the maximum value at 15 years old. Girls' outcomes show a progressive increase in bodyweight through age increases, obtaining maximum values at 16-16.5 years. Similar results were found for height since a progressive increase until 15 years was reported, when height stabilises. BMI follows a progressive and constant increase until 16 years, where its maximum value is reached.  Tables 2 and 3 illustrate the comparative of our bodyweight, height and BMI values and others reported in a previous cross-sectional study by Sobradillo et al. [11] for boys and girls, respectively. Between-study comparison outcomes for bodyweight shows significant differences in bodyweight between 12 and 13 years old in both gender (boys: p < 0.001; girls: p < 0.001 to 0.003) and at 14 years old (boys: p = 0.002; girls: p = 0.005). A meaningful difference was also found in boys at 15 (p < 0.001), 16.5 (p = 0.001) and 17 years (p < 0.001). Regarding height, significant differences were reported in boys at 12 (p < 0.001), 13 (p < 0.001), 14.5 (p = 0.027), 15 (p = 0.005), 16.5 (p < 0.001) and 17 (p < 0.001) years, while girls' outcomes only revealed differences at 12 (p < 0.001), 12.5 (p < 0.001), 14.5 (p < 0.001) and 15.5 (p = 0.009) years. Likewise, BMI comparisons also showed differences between studies. Coincidently, there were significant differences for BMI in both gender at 12 (boys: p = 0.032; girls: p < 0.001), 12.5 (boys: p = 0.001; girls: p < 0.001), 13 (boys: p = 0.027; girls: p = 0.007), 14 (boys: p = 0.007; girls: p < 0.001) and 15 years old (boys: p < 0.001; girls: p = 0.030). Moreover, meaningful differences were found at 16 (p = 0.034) and 14.5 years (p = 0.012) for boys and girls, respectively.   Tables 4-6 displays the percentile distribution of bodyweight, height, and BMI, respectively, by gender and age.

Discussion
The main findings of the present study show significant differences in bodyweight, height and BMI growth charts between the studied population and the reference parameters applied in the Extremadura Health System [11], for numerous age and gender groups, as previously reported studies in other regions from Spain [4,11]. These studies also showed relevant differences in some age groups for bodyweight, height, and BMI. Thus, these results question the use of one or other data as state-wide references. Therefore, taking as national reference the data reported by only one community or several communities may not be representative for the development of children and adolescents from other regions of the same country. Moreover, the situations of thinness, overweight or obesity could be normalised if inappropriate or unrepresentative benchmarks are applied.
More specifically, when comparing our study with the two previous studies [4,11], results show that bodyweight progressively increases with age in boys, finding a pronounced increase at 15 and 15.5 years old in our study and the study by Sobradillo et al. [11]. However, this pronounced increase was not found by Lezcano et al. [4]. Coincidently, the maximum values for all three studies were reached around 17 years old, being lower in our study. Similarly, the results also show a progressive increase in bodyweight with age in girls. The maximum value is reached at 16 years old and stabilises thereafter, in agreement with previous studies [4,11].
Regarding height, both genders experienced a progressive increase with age, reaching a maximum value at 16 years old. Female results agree with those reported by previous studies [4,11]. In contrast, previous studies reported a considerable increase in height (more than 3 cm) between 16 and 17 years in males [4,11] that was higher than our study outcomes.
As well as bodyweight and height, BMI increased progressively with age, in line with the findings previously presented by Sobradillo et al. [11], with a noticeable increase around 15 and 15.5 years as in our outcomes. However, this increase was not found in the cross-sectional study conducted by Lezcano et al. [4], which only showed a progressive increase in BMI with age. Coincidentally, the three studies showed maximum BMI values at 17 years old. Despite the similarities found between our study and the study by Sobradillo et al. [11], the comparative results show significant greater BMI values compared to the outcomes presented by Sobradillo et al. [11] for several age groups between 12 and 15 years. However, our BMI values were quite similar to those presented by Lezcano et al. [4]. A pronounced increase in females BMI was also observed at 16 years old, reaching a maximum of 22.38 kg/m 2 , like previous studies [4,11]. Furthermore, significant differences were found between our female BMI outcomes and those reported by Sobradillo et al. [11], for most age groups between 12 and 15 years (Table 3). Contrarily, our BMI outcomes are very similar to those obtained by Lezcano et al. [4], as happens in males.
The differences and similarities found with the studies by Sobradillo et al. [11], and Lezcano et al. [4], respectively, may be due to different reasons. Firstly, the territorial representativeness of the selected sample in every study. While Sobradillo et al. [11] obtained data from children and adolescents from a single region of Spain, Lezcano et al. [4] based their results on several autonomous communities. Furthermore, the disparity in the level of physical-sport activity between the different regions of Spain could also explain these differences. It has been shown that regions with a higher level of organised physicalsports activity have a lower rate of childhood obesity [25]. Specifically, when comparing the regions of Extremadura and Basque Country, a lower percentage of children doing organised sport in Extremadura than in Basque Country was observed (70% vs. 85% in boys and 44% vs. 70% in girls). In fact, the rate of sedentarism is 37% in Extremadura compared to 28% in the Basque Country [25].
It should be known that there are socio-demographic variables, such as socio-economic level or region [26], as well as cultural variables, that must be considered because they affect the problem. These variables must be studied if we want to carry out adequate and effective preventive programmes and strategies [27]. Considering socio-demographic factors, the differences found with respect to anthropometric parameters between children and young people in the communities of the Basque Country and Extremadura could be based, among other reasons, on the economic and educational level of both regions. Data from the State System of Education Indicators of the Ministry of Education [28] indicate that the graduation rate in compulsory secondary education in the Basque Country exceeds 70%, while in Extremadura, it is below the national average. The autonomous community with the highest gross rate of Baccalaureate graduates is the Basque Country and in terms of the rate of higher education graduates the Basque Country is in second place. However, Extremadura is at the bottom of both rankings.
According to Eurostat 2008 [29], the Gross Domestic Product (GDP) of Extremadura is 18,250 million, the GDP per capita is 16,720 euros, the unemployment rate is 18.1% and the risk of poverty is 35.3%; while the Basque Country has a GDP of 66,779 million, a GDP per capita of 30,819 euros, an unemployment rate of 8.5% and a poverty risk of 9.1%.
Furthermore, these differences between regions could also be conditioned by the classification of urban (Basque Country) and rural (Extremadura) environments. In urban environments, the access to sports facilities, team-programmed activities, transport networks, etc., can directly influence adherence to a lifestyle and affect physical activity practices or the following of healthy diets [30,31]. The Quality of Life Indicator [14] established by Eurostat, which is multidimensional in nature (material living conditions, work, health, education, leisure, etc.), could explain the differences between regions in the rates of growth and overweight/obesity in Spain [32,33].
There is also evidence of a direct relationship between long-term acceleration of growth and more favourable socio-economic and health conditions (nutrition and/or absence of disease). Thus, these allow the phenotypic expression of the maximum genetic potential for growth in the child and adolescent population [34]. For example, if we take the Human Development Index of the different Spanish Autonomous Communities as an indicator of educational, economic and health levels, the Basque Country ranks as the most developed Autonomous Community in contrast to Extremadura, which is at the bottom of the list [15]. Therefore, the reference values included in the growth tables may not be applicable from one region to another, mainly due to the difference in context and environments.
In summary, the comparison of anthropometric parameters of children and young people with specific graphs from other communities that do not correspond to their own, can lead to mistakes when these children grow by percentiles higher or lower than those stipulated as maximum or minimum [35]. Moreover, it could normalise situations of anthropometric imbalances. The existence of differences between both percentile distributions could make visible the need to use new indicators, adapted to the physical and anthropometric reality of children and young people to avoid the possible normalisation of situations of thinness, overweight or obesity.
One of the strengths of this study is the representativeness of the sample, as it was 4130 children and young people from Extremadura between 12 and 17 years old, compared to the sample of the study used to elaborate the reference tables by Sobradillo et al. [11] (6443 children and young people from Basque Country aged between 0-18 years). In addition, the comparison has been made between data obtained in similar years and is therefore more reliable. If current data were used to make the comparison, the differences could be even greater probably, due to the increase in obesity levels in recent years [4,[8][9][10][11]. Nevertheless, this study also presents several limitations. Considering that the main differences occur at the youngest ages, very markedly in girls, it is necessary to point out that the present study has the limitation of having focused on individuals over 12 years old. Thus, future studies focusing on younger ages than 12 years would be of great interest. Moreover, our study does not allow us to predict how the development of these children and young people will behave, since due to its cross-sectional design it is not possible to know the growth rate of participants. In addition, it should be considered that both girls and boys have not yet been completed the muscle and skeletal development at these ages. Thus, it would be interesting if future studies consider the influence of chronological and biological age on the monitored parameters.

Conclusions
The findings of this study showed that bodyweight, height and BMI of children and young people from Extremadura differ from the reference values proposed by the Faustino Orbegozo Eizaguirre Foundation that are currently used in the Extremadura Health Service. Moreover, the development-associated changes of children and young people from Extremadura compared to those from Basque Country raise the question of which values should be considered to define the levels of development and growth in the current population. Thus, we conclude that the reference values used by Extremadura Health Service may not be applicable to children and adolescents from Extremadura due to the different contexts of regions.
Hence, this study presents growth tables and graphs adapted to the physical and anthropometric reality of Extremadura adolescents. Therefore, the results presented in this study could be an important contribution to the need to use new indicators, adapted to the physical and anthropometric reality of children and young people to avoid the possible normalisation of situations of thinness, overweight or obesity. Funding: This research was funded by Extremadura Health Service, grant number 041/06. The funders played no role in the study design, the decision to publish, or the preparation of the manuscript.

Institutional Review Board Statement:
The study was conducted according to the guidelines of the Declaration of Helsinki and was approved by the Bioethics Committee of the University of Extremadura reference code (11/2006).

Informed Consent Statement:
Informed consent was obtained from all subjects involved in the study.

Data Availability Statement:
The datasets used during the current study are available from the corresponding author on reasonable request.