We obtained deidentified data from 2 primary care electronic health records databases: the BIFAP (Base de Datos para la Investigación Farmacoepidemiológica en Atención Primaria [Database for Pharmacoepidemiological Research in Primary Care]) and the SIDIAP (Sistema de Información para el desarrollo de la Investigación en Atención Primaria [Information System for Research in Primary Care]). Both rely on data from the regional health services integrated in the Spanish national health system, which provides universal access to health care to the entire Spanish population. Both databases contain demographic data and height and weight measurements recorded at repeated intervals during childhood and adolescence by pediatric primary care health professionals. BIFAP is a multiregional dataset that, in 2017, contained data for 9.4 million people from 7 out of the 17 autonomous regions of Spain, starting in 2001.18 The data are provided by primary care health professionals on a voluntary basis in some regions and include the entire population in others. At the time of the study, BIFAP included data from of 6857 primary care physicians (5862 general practitioners and 995 pediatricians) from 7 regions (Aragon, Asturias, Cantabria, Castile and Leon, Madrid, Murcia, and Navarre). This yields a total of 9.4 million patients, representing 67% of the population of these regions (14 million) and 20% of the total Spanish population (46.5 million). The population of BIFAP is representative of the population receiving health care in the Spanish national health system,18 which covers nearly the entire population (99.02% in 2017). For its part, SIDIAP contains data on nearly 6 million people from 286 primary care health centers in the region of Catalonia starting in 2005.19 The population of SIDIAP is highly representative of Catalonia in terms of geographical, age, and sex distributions.20

In this prospectively-collected longitudinal study, we included all children and adolescents registered in BIFAP and SIDIAP between the ages of 2 and 17 years with at least 1 height and weight measurement recorded during the same primary care visit from 1 January 2005 to 31 December 2017 (or from 1 January 2011 for Castile and Leon).

Height and weight were routinely measured in a standardized fashion by trained pediatric primary care health professionals as part of the health promotion program “Programa de Salud Infantil” (Childhood Health Program).21 The program recommends measuring height and weight at several key points during childhood and adolescence: at 2 years, 3 to 4 years, 6 to 7 years, 8 to 9 years, 12 years, and 14 years.21 Body mass index (BMI) was calculated as weight (in kilograms, kg) divided by height (in meters, m) squared. Overweight and obesity were defined using the age- and sex-specific BMI z-scores (zBMI) from the World Health Organization (WHO) growth standard and growth reference.22,23 Overweight was defined as a zBMI greater than+2.0 in children younger than 5 years or greater than+1.0 in those older than 5 years. Obesity was defined as a zBMI greater than+3.0 in children younger than 5 years or greater than+2.0 in those older than 5 years. Extreme values of height, weight and BMI (zBMI>±5.0) were removed.24 If a child had more than 1 BMI measurement for the same age or study year, we considered the most recent available BMI measurement. Biologically-implausible values of height and weight were removed.24,25

We calculated overweight and obesity prevalence and 95% confidence intervals (95%CI) as the percentage of children with overweight (including obesity, denoted by overweight/obesity) or obesity from the entire study population, stratified by age, sex, study year, and region. We grouped age into 3 categories (2-5 years, 6-11 years, and 12-17 years) to evaluate prevalence trends. We calculated P-trends using a logistic regression model with study year as a continuous variable and overweight/obesity and obesity (vs nonoverweight/obesity or no obesity) as a binary variable. Next, we calculated the percent change of prevalence between the years 2005 to 2017 by dividing the difference of the prevalence in 2005 and 2017 by the prevalence in 2005 and multiplying by 100.

For all children with at least 2 recorded BMI measurements, we calculated overweight/obesity incidence rates (for children with normal weight at baseline) and obesity incidence rates (for children with normal or overweight at baseline). Children were followed up until they developed overweight/obesity (if they were of normal weight at baseline), obesity (if they were of normal weight or overweight at baseline), turning 18 years old, reaching the end of the study (31 December 2017), death, or being transferred out. Incidence rates were calculated by dividing the number of new cases of overweight or obesity by 100 person-years. Person-years are the time (in years) that a child is at risk of developing overweight/obesity or obesity during a specific age period. Because the number of observations was higher in even-numbered ages (especially at ages 4, 6, 8, 12, and 14 years), age periods were grouped into 2 consecutive years (2-3, 4-5, 6-7, 8-9, 10-11, 12-13, 14-15, and 16-17 years). To observe incidence trends, we estimated the incidence rates during 2 time periods: from 1 January 2006 to 30 June 2011 and from 1 July 2011 to 31 December 2017.

Our presentation of the results focuses primarily on the prevalence and incidence of obesity, with the results of overweight/obesity provided in the tables of the supplementary data. All the above analyses were conducted in R.26 This study was approved by the scientific committee of BIFAP (code: 06_2018) and the Ethics committee of IDIAPJGol (code: P16/179).

The study populations included 2504568 children with 7613323 BMI measurements from 8 Spanish regions. A total of 1278045 children (51% of the study population) were boys. Overall, the study population had an average baseline age of 6.2 years (standard deviation [SD] 4.6), were followed up for an average of 7.5 (SD, 4.0) years and had an average of 3.5 BMI (SD, 2.9) measurements during follow-up (table 1); 35.6% and 14.2% of the children had at least 1 measurement indicating overweight/obesity and obesity during follow-up, respectively (table 1). Children living in Catalonia had the longest average follow-up time (8.8 years; SD, 3.9) whereas children living in Castile and Leon had the shortest follow-up time (4.8 years; SD, 2.0). The population from Navarre and Catalonia had the highest and lowest average number of BMI measurements, respectively (Navarre, 9.0 vs Catalonia, 3.9 BMI measures per child) (table 1 of the supplementary data).

The overall prevalence of obesity increased in boys and girls, starting at age 2 years (0.8%; 95%CI, 0.8-0.9 in both sexes) until peaking at age 7 years in girls (17.3%; 95%CI, 17.1-17.5) and age 9 years in boys (24.1%; 95%CI, 23.9-24.3), before decreasing until age 14 years (table 2 of the supplementary data and figure 1). After age 14 years, there was a slight increase until age 17 years in both sexes (from 10.6%; 95%CI, 10.5-10.7 at age 14 years to 13.4%; 95%CI, 13.0-13.7 at age 17 years in boys, and from 6.7%; 95%CI, 6.6-6.8 at age 14 years to 10.2%; 95%CI, 10.0-10.5 at age 17 years in girls) (figure 1 and table 2 of the supplementary data). The prevalence of overweight/obesity followed roughly this same trend. The prevalence of overweight/obesity peaked in both sexes at age 9 years (46.6%; 95%CI, 46.6-46.9 in boys and 43.7%; 95%CI, 43.5-44.0 in girls) before decreasing until age 14 years (table 3 of the supplementary data).

Figure 1.

Prevalence of obesity by sex and age in 2 504 568 children in the overall population and by region. Each dot represents the prevalence of obesity for each child age and applied a weighted loss smoother to observe the trends over time. The last measurement was used for the same age year if a child had more than one BMI measurement.

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All regions followed a similar pattern to the overall prevalence of obesity (figure 1 and table 2 of the supplementary data). The highest obesity prevalence was observed in Murcia at age 9 years, especially in boys (34.5%; 95%CI, 30.6-38.4) compared with girls (30.4%; 95%CI, 26.9-33.9). The lowest prevalence was observed in Navarre at age 9 years (21.0%; 95%CI, 20.0-21.9 in boys and 14.2%; 95%CI, 13.4-14.9 in girls) (table 2 of the supplementary data). In Asturias, Cantabria, Catalonia, and Madrid, the prevalence of obesity was slightly higher than the overall prevalence of obesity, whereas in Aragon and Castile and Leon the prevalence was similar to the overall prevalence of obesity (figure 1 and table 2 of the supplementary data). The highest prevalence of overweight/obesity was also found in Murcia and the lowest prevalence in Navarre (table 3 of the supplementary data).

Overall obesity trends decreased in all age-sex groups from 2005 to 2017 (figure 2 and table 4A,B of the supplementary data). In boys ages 6-11 years, the overall prevalence of obesity decreased from 19.5% (95%CI, 9.2-19.8) in 2005 to 17.6% (95%CI, 17.4-17.8) in 2017 (figure 2 and table 4A of the supplementary data), corresponding to a 9.7% change (figure 3 and table 4A of the supplementary data). Although the prevalence was low compared with that in other age groups, the largest decreases were generally found in ages 2 to 5 years. For example, for boys, the overall trend at ages 2 to 5 years fell from 3.0% (95%CI, 2.9-3.1) in 2005 to 2.1% (95%CI, 2.0-2.2) in 2017 (figure 2 and table 4A of the supplementary data). These changes corresponded to a 30.0% decrease (table 4A of the supplementary data). The overall prevalence of overweight/obesity followed a similar decreasing trend (table 5A,B of the supplementary data). For example, in boys aged 6 to 11 years, the overall prevalence of overweight/obesity decreased from 42.2% (95%CI, 41.8-42.5) in 2005 to 37.8% (95%CI, 37.5-38.1) in 2017, corresponding to a 10.4% change (table 5A of the supplementary data).

Figure 2.

Prevalence trends of obesity between 2005 and 2017 by sex, age groups (2-5 years, 6-11 years, 12-17 years), and region. Each dot represents the prevalence of obesity for each child age and applied a weighted loss smoother to observe the trends overtime. The last measurement was used for the same age year if a child had more than one BMI measurement.

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Figure 3.

Percent change in the prevalence of obesity between 2005 and 2017 by age, sex, and region. The percent change of prevalence from 2005 to 2017 was calculated by dividing the difference between the prevalence in 2005 and 2017 by the prevalence in 2005 and multiplying by 100. For Castille and Leon the difference was calculated between 2010 and 2017.

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The prevalence of obesity decreased over time in nearly all regions, especially among children aged 2 to 5 years (figure 2). However, slight differences were observed especially for girls aged 6 to 11 years and 12 to 17 years in Aragon, Cantabria and Navarre where the prevalence fell only gradually, or even increased (figure 2 and table 4B of the supplementary dada). For example, for girls aged 12 to 17 years in Navarre, prevalence increased from 6.6% (95%CI, 5.7-7.4) in 2005 to 8.3% (95%CI, 7.4-9.2) in 2017 (figure 2 and table 4A,B of the supplementary data). Prevalence decreased in most other regions, particularly in Murcia for girls aged 12 to 17 years, where the prevalence decreased from 15.4% (95%CI, 10.8-20.0) in 2005 to 12.4% (95%CI, 9.9-14.9) in 2017. The overweight/obesity trends decreased in all regions and in both sexes among children aged 2 to 5 and 6 to 11 (table 5A,B of the supplementary data). Similar to the prevalence of obesity, that of overweight/obesity in girls decreased more gradually than in boys and increased in Aragon, Catalonia and Navarre in ages 12-17 years (table 5A,B of the supplementary data).

The overall incidence rate of overweight and obesity peaked between the ages of 6 to 7 years in both sexes (figure 3 and table 6 of the supplementary data). After this peak, the incidence rates continued to decrease into adolescence. The number of new obesity cases per 100 person-years was 4.5 (95%CI, 4.5-4.5) in boys and 3.5 (95%CI, 3.5-3.5) in girls aged 6 to 7 years (figure 3 and table 6 of the supplementary data). Obesity incidence rates were highest in Murcia for both sexes (6.6; 95%CI, 6.1-7.1 in boys and 4.7; 95%CI, 4.3-5.1 in girls aged 6 to 7 years) and were lowest in Navarre (4.0; 95%CI, 3.9-4.2 in boys aged 6 to 7 years and 3.2; 95%CI, 3.0-3.3 in girls aged 6 to 7 years) (figure 3 and table 6 of the supplementary data). The incidence rates by region followed a similar pattern as the overall incidence, except for Asturias and Murcia where we observed low incidence rates in both sexes in ages 8 to 9 years (1.6; 95%CI, 1.4-1.9 and 0.8; 95%CI, 0.6-1.0 in boys living in Asturias and Murcia, respectively) and high incidence rates between ages 10 and 11 years (2.9; 95%CI, 2.6-3.3 and 4.0; 95%CI, 3.5-4.4 in boys living in Asturias and Murcia, respectively). Overweight/obesity incidence rates followed roughly the same trend as obesity for age, sex, and region (table 7 of the supplementary data). Additionally, we observed that the overall incidence of overweight/obesity and obesity decreased from the first to the second period in all age groups and both sexes (table 8 of the supplementary data). We could not calculate incidence trends by region due to the small sample size and confidentiality issues (figure 4).

Figure 4.

Incidence rate (number of new cases/100 person-years) of obesity by sex, age and region.

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One of the main strengths of our study, in addition to its sample size and longitudinal design, is the availability of repeat measurements of weight and height for the same child. Furthermore, we were able to evaluate prevalence trends for 8 Spanish regions using the same study design and only 2 databases. Both of these databases are representative of the Spanish population, allowing our results to be interpreted with high external validity.

However, our study has some limitations. First, we were limited to studying the regions for which data were available through the SIDIAP and BIFAP. Consequently, our results likely underestimate national overweight and obesity prevalence, but are representative of the specific regions of Spain.9,12,13 Next, we only had data available on children who used the public Spanish health care system. Within the public health care system, obesity may be slightly overestimated as children with obesity have more medical visits than healthy children. However, all the regions have implemented the Childhood Health Program (Programa de Salud Infantil), which recommends several medical appointments at key points during childhood to combine preventive and health promotion activities. Due to the standardized timeline of the Childhood Health Program included in the public health care system, and our large sample size, we expect obesity overestimation to be minimal. Finally, we did not have additional information of other sociodemographic factors such as socioeconomic status or nationality, which are known to affect childhood obesity prevalence and incidence differently.14