Introduction
Early childhood is a critical stage of life, marked by significant physical and neural development. Particularly, early childhood overweight and obesity is a growing public health concern worldwide. Early childhood overweight and obesity not only lead to adverse consequences including physical and mental health disorders [
1,
2], but also results in impacts on the later adulthood life, such as an increased risk of diabetes, osteoarticular diseases, cardiovascular diseases, and cancer [
2]. The pooled prevalence estimates of obesity and overweight in European children (aged 2–7 years) was 22.2% from 2006 to 2016 [
3], which was higher than those in Africa (10.4%), North America (12.1%), Asia (5.7%) and Latin America and the Caribbean (7.0%), and other developing countries(7.2%) during same period [
4]. According to the results of the German Health Interview and Examination Survey for Children and Adolescents, the prevalence of overweight among preschool children in Germany was 10.8% for female children and 7.3% for male children, and the prevalence of obesity was 3.2% for female children and 1.0% for male children between 2014 and 2017 [
5].
Existing studies show that the trend of overweight and obesity in preschool children are changing. A study performed in Bavaria showed an increasing trend from 1982 to 1997 [
6]. Another investigation covering all of Germany conducted during 1991 to 2000 also indicated the same trend [
7]. In comparison, the trend was decreasing in 16 German federal states from 2004 to 2008 [
8]. A similar decreasing trend was also observed in the results of the German Health Interview and Examination Survey for Children and Adolescents between 2014 and 2017 [
5]. Although Germany has achieved the WHO target for controlling obesity among children and adolescents, the prevalence of obesity remains at a high level. Overweight and obesity could already lead to lower life satisfaction [
9] and more school bullying [
10] than that of normal children in early childhood, and these consequences of obesity can carry on into adulthood [
11]. Therefore, it is important from a public health perspective to rigorously evaluate the development of overweight and obesity with large and high-quality samples at a regional level, as well as contextualize them internationally. This study is the first to describe the trend of overweight and obesity stratified by socioeconomic characteristics using a dataset involving 37,858 preschool children in Heidelberg. In addition, the up-to-date estimates are essential to fill the gap of studies on the trend of overweight and obesity in Germany before 2018.This study aims to explore how the prevalence of overweight and obesity during early childhood varies by age, sex, and migration background at the regional level over time by means of a large dataset from the School Entry Health Examination (SEHE), which includes all preschool children in the Rhine-Neckar County and the City of Heidelberg, Germany from 2013 to 2018 [
12]. This study may provide evidence for local health policymakers at regional levels to implement programs for primary prevention of obesity.
Discussion
This cross-sectional study showed that the BMI distribution and the prevalence of overweight and obesity among preschool children aged 4–6 years in the Rhine-Neckar County and the City of Heidelberg increased between 2013 and 2018. After adjusting for age, sex, and migration background, the significant increasing trend of overweight was only detected among 5-year old male children with migration backgrounds. The upward trend of obesity was observed only for male children aged 5 years and for female children aged 6 years with migration backgrounds. This is the first population-level study that uses a dataset with such a large sample of School Entry Health Examination data to illustrate the time trends of overweight and obesity among preschool children in Rhine-Neckar County and the City of Heidelberg.
Our study demonstrated that the BMI distribution was increasing, which was consistent with studies by Jena et al. [
20] and Aachen et al. [
21]. In recent decades, although the global trend of overweight and obesity among children has been increasing [
22], previous studies reported that the prevalence of overweight and obesity among German preschool children showed a downward trend after 2004 [
6,
7,
23]. From the second wave of the German Health Interview and Examination Survey for Children and Adolescents during 2014 to 2017, the national trend of overweight and obesity decreased from 13% in 2003 to 11% in 2017. In Europe, the trend also remained stable and even decreased from 30.3% to 25.6% during 1999 to 2016 [
24]. Prevalence of other countries such as Australia (22.5% in 2006 to 21.6% in 2018) and Canada (30.7% in 2004 to 27.0% in 2013) also have the same trend as Europe. However, our study showed an opposite trend that the prevalence increased from 8.9% to 10.2% between 2013 and 2018, but remained a lower level than that of Germany and Europe. It has similar trends compared to China (8.8% in 2006 to 10.1% in 2014) [
25] and the United States (7.2% in 2006 to 9.4% in 2018). The cause of this phenomenon may be that the trend of overweight and obesity varies widely in federal states [
8], and different measurement or assessment methods of obesity [
23] were conducted in different regions. Another reason could be that migration background is regarded as a potential health determinant for the prevalence of overweight and obesity [
26]; Rhine-Neckar County and the City of Heidelberg belongs to Baden-Württemberg, where the proportion of people with an migration background accounted for the top three states in Germany [
27]. Besides, previous studies provided clear evidence of a significant association between migrant status and less use of preventive services [
28]. All of the above factors may lead to an increasing trend in the prevalence of overweight and obesity. Although the German government has emphasized controlling obesity in the National Sustainable Developmental Strategy in 2016 [
29], it remains difficult to apply health promotion and prevention measures to young children, especially for preschool children. Decreased energy expenditure or increased energy intake was regarded to be the cause of increasing obesity [
30]. Many countries have established recommendations regarding the amount of time children and adolescents should take part in physical activities [
31]. Due to the different type of kindergartens and their possible space limitations, it is difficult to quantify the intensity and time of physical exercise available for preschool children. Although one study showed that preschool children were more physically active on forest playgrounds than on traditional playgrounds [
32], the forest kindergartens only accounted for a small proportion in Rhine-Neckar County and the City of Heidelberg. Besides, preschool children usually spend a lot of time with parents, and parenting style greatly affects children’s behavior [
33,
34], including different diet types and use of visual media, which may influence children’s weight and/or height. Previous studies which indicated the same correlation between parenting style and obesity also showed similar trends of overweight and obesity among preschool children in Bavaria from 1982 to 1997 [
6] and in the City of Aachen from 1968–1999 [
21]. Taken together, our findings indicate that the government should develop and propagate appropriate policy, if possible, adapted to the type of kindergarten, and help parents establish healthy parenting styles.
Although the general prevalence of overweight and obesity in Rhine-Neckar County and the City of Heidelberg showed an upward trend, after adjusting by age, sex, and migration background, the increasing trend of overweight and obesity was only observed among male children aged 5 years with migration backgrounds and female children aged 6 years with migration backgrounds. Migration background has already been regarded as an independent potential risk factor for overweight and obesity in earlier studies [
35‐
38]. Previous studies [
39,
40] have indicated an increasing trend of overweight and obesity in children from lower socioeconomic status compared with children from medium to higher socioeconomic status. Meanwhile, different culture and life style, dietary habits, physical activity, parents’ overweight, breast feeding, or media consumption all played crucial roles for childhood obesity in children with migration backgrounds [
33,
34]. We also found discrepancies in trends of overweight and obesity after adjusting for age, which were similar to previous findings [
5,
41,
42] which found that the prevalence of overweight and obesity increased with age. This disparity may be related to the period of adiposity rebound occurring between 4 and 7 years old [
43,
44]. Previous studies showed that the capacity of infants and young children to control their food intake is affected by feeding pattern and eating control of mothers [
45]. When children become more autonomous and more in control of their food intake when growing older, their ability to regulate energy balance may be damaged, which could lead to obesity [
44]. Targeted intervention projects are warranted for vulnerable groups, especially for children aged 5–6 years, to optimize the preventive measures.
Our study used a large cross-sectional dataset collected between 2013 and 2018 from the successive surveillance of SEHE, which involved all preschool children in Rhine-Neckar County and the City of Heidelberg. Our sample size was representative of the general preschool population of Rhine-Neckar County and the City of Heidelberg and was able to display the secular trend. Moreover, after adjusting by sociodemographic factors, it realistically reflects the trend of overweight and obesity in this area, which could offers formative evidence to regional policy-makers for preventing and controlling the prevalence of overweight and obesity among vulnerable groups.
Our study has several limitations. Firstly, since this study was based on a cross sectional study design, it could not assess temporality. Secondly, the trend we evaluated was adjusted only by age, sex, and migration background, and other sociodemographic factors should be investigated in further research. Thirdly, our results only represented preschool children from Rhine-Neckar County and the City of Heidelberg, and it may be difficult to generalize this to other populations.
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