Socioeconomic Status, Overweight, and Obesity in Childhood and Adolescence

Secular trends from the nationwide German KiGGS study

Background: Overweight and obesity in early life increase the risk of chronic disease and ill health later on. We studied secular trends in the prevalence of overweight and obesity among young people in Germany, with consideration of socioeconomic status (SES).

Methods: We used repeated cross-sectional data from 3– to 17-year-olds from the German Health Interview and Examination Survey for Children and Adolescents (KiGGS). Overweight and obesity were defined according to the body mass index, based on measured height and weight from the KiGGS baseline survey (2003–2006) and the KiGGS second wave (2014–2017). SES was assessed with a composite index of parental education, occupation, and income.

Results: In both study periods, the prevalence of overweight and obesity was highest among girls and boys from families of low SES. In the group with lowest SES, the prevalence of overweight rose from 20.0% in 2003–2006 (95% CI [18.0; 22.1]) to 25.5% [20.5; 31.2] in 2014–2017 (p = 0.043). Thus, social differences in the prevalence of overweight increased over time. No such trend was found for the prevalence of obesity.

Conclusion: Social differences in the prevalence of overweight among children and adolescents increased from the early 2000s to the mid-2010s. Structural measures are needed to help prevent overweight among young people in socially disadvantaged circumstances.

Overweight and obesity in childhood and adolescence are a worldwide health problem. They represent one of the most important public health challenges in terms of noncommunicable diseases in the 21st century (1). The relationship between overweight or obesity and socioeconomic status (SES) in childhood and adolescence has long been known internationally and shows that not all population groups are affected with equal frequency (2, 3). The lower the SES, the higher is the prevalence of overweight and obesity (4).

Numerous studies from Germany also demonstrate a socially unequal distribution of overweight and obesity to the detriment of children and adolescents from socially disadvantaged families (5, 6). Results from the last survey of the German Health Interview and Examination Survey for Children and Adolescents (KiGGS second wave, 2014–2017) confirm that 3- to 17-year-old children and adolescents with low SES are more likely to be affected by overweight or obesity compared to their peers from socially better-off families (7). Although observations for Germany suggest overall that overweight and obesity prevalences are no longer rising or that the trend is slowing down or stagnating (8, 9, 10, 11), trends in overweight and obesity prevalences for different SES groups in Germany have not been investigated in more detail.

The fact that overweight and obesity in childhood and adolescence, like their socially unequal distribution, often persist into adulthood presents considerable potential for prevention: compared to their normal-weight peers, children and adolescents with overweight and in particular obesity more frequently exhibit risk factors for cardiovascular diseases such as high blood pressure, dyslipidemia, and glucose metabolism disorders (12). Moreover, a high body mass index (BMI) in childhood and adolescence is associated with a higher probability for type 2 diabetes, hypertension, and cardiovascular diseases in adulthood (13). In addition, the discrimination, bullying, and stigmatization experienced due to body weight can have long-term effects on mental health (14, 15).

This analysis of KiGGS data investigates the temporal trend in overweight and obesity prevalence stratified by SES, as well as the magnitude of socioeconomic differences in prevalence.

Methods

The analyses are based on data from the KiGGS study, which has been conducted nationwide since 2003 as part of health monitoring at the Robert Koch Institute (16). The first cross-sectional survey (the KiGGS baseline survey) was carried out between 2003 and 2006 as a combined investigation and questionnaire survey in a total of 167 federal German municipalities (sample points). The selection of sample points was carried out according to a stratified approach (stratification characteristics: federal state and type of municipality) proportional in size to the 0- to 17-year-old resident population of the municipalities. This ensured that the selected municipalities reflected the settlement structure of Germany according to federal state, type of municipality, and resident population in relation to the population of children and adolescents (17). The addresses of children and adolescents were selected from the residents’ registration office of these municipalities according to a stratified random procedure (unrestricted random selection, stratified according to years of age). In order to obtain a sufficient number of participants with a migrant background, children and adolescents of non-German citizenship were oversampled. A total of 17 641 children and adolescents (8656 girls, 8985 boys) aged 0–17 years took part (response rate 66.6%).

In addition to physical examinations, interviews conducted by physicians, a variety of tests, and laboratory analyses, the survey program included written questionnaires completed by the parents or, if aged over 11 years, the children and adolescents themselves (18). The second cross-sectional survey (KiGGS first wave) was carried out in the form of a telephone survey between 2009 and 2012 and did not include the collection of examination data. Since examination data on body weight and height were the focus of the present analysis, the KiGGS first wave was not considered in this evaluation.

The third representative cross-sectional survey (KiGGS second wave) was carried out again from 2014 to 2017 as a combined examination and interview survey (19). A new stratified random sample was drawn from the population registers of the 167 sample points in the KiGGS baseline survey. A randomly selected sub-sample of children and adolescents aged 3–17 years were invited for an examination and an interview, while a further sub-sample of children and adolescents aged 0–17 years were invited for an interview only. A total of 3567 children and adolescents (1801 girls, 1766 boys) took part in the examination program (response rate 41.5%) (20). For the present analysis, the study populations of the baseline survey and the examination program in the second wave were limited to the standardized age range of 3–17 years (Table 1).

Table 1

Characteristics of the study population

Overweight and obesity

In the KiGGS baseline survey and the KiGGS second wave, the height and weight of participants aged 3–17 years were measured in a standardized manner. BMI was calculated as the ratio of body weight to height squared (kg/m²). Since there is no standardized threshold value for overweight and obesity in childhood and adolescence, percentile curves are used at this age to map the distribution of BMI taking into consideration age and sex in a reference population. In Germany, overweight (>90^th percentile, including obesity) and obesity (>97^th percentile) are defined using the reference system according to Kromeyer-Hauschild et al., which was presented in an updated form in 2015 (21, 22). In the present analysis, the prevalences in the KiGGS baseline survey and the KiGGS second wave were calculated according to the updated reference system.

Socioeconomic status

Socioeconomic status (SES) was calculated in a standardized manner in all KiGGS waves on the basis of parent information on school and vocational educational attainment, occupational status, as well as needs-weighted net household income (equivalized disposable income) . For each of these three socioeconomic indicators (education, occupation, income), point scores from 1.0 to 7.0 were determined, reflecting the relative status of families in the respective SES dimension in each survey period. The scores were added up equally weighted to form an additive SES index (score range, 3.0–21.0). The process of determining scores and forming an index was revised in the KiGGS first wave and subsequently applied equivalently to the baseline survey and the second wave. A detailed description can be found in Lampert et al. (23, 24). Based on index value, a distribution-based assignment to three SES groups was carried out for each KiGGS wave: children and adolescents from households of low (1^st quintile), middle (2^nd–4^th quintile), and high (5^th quintile) SES.

Statistical methods

The prevalence of overweight and obesity was calculated with a 95% confidence interval (CI) and stratified by time period, sex, and SES. Differences between the two time periods were analyzed using Pearson’s χ² test. The magnitude of social differences in the prevalence of overweight and obesity was determined using the Slope Index of Inequality (SII) and the Relative Index of Inequality (RII) (25, 26, 27). Whereas the SII quantifies the magnitude of absolute differences (prevalence difference) between lowest and highest SES, the RII gives the magnitude of relative differences (prevalence ratio) between lowest and highest SES (see the eMethods Section for more details). By means of weighting, the samples were adjusted to the official population statistics in terms of age, sex, federal state, nationality, and parental education. All analyses were performed with the survey procedures in Stata 15.1 (StataCorp LP, College Station, TX, USA) taking into account weighting and cluster design effects.

Results

Table 2 shows the prevalence of overweight and obesity calculated on the basis of KiGGS data. In the total group of 3- to 17-year-old children and adolescents, no changes can be seen for either overweight or obesity prevalence from the KiGGS baseline survey (2003–2006) to the KiGGS second wave (2014–2017). This applies equally to boys and girls.

Table 2

Prevalence of overweight and obesity according to sex and time period among 3- to 17-year-olds in Germany

If the prevalence estimates for the three SES groups are performed separately, one sees strongly pronounced social gradients: The lower the family SES of children and adolescents, the higher the probability that they are affected by overweight or obesity (eTable). These social gradients are apparent in both survey periods for boys as well as girls.

eTable

Prevalence of overweight and obesity according to time period and socioeconomic status among 3- to 17-year-olds in Germany

Differences between the SES groups can also be observed in terms of secular trends (Figure, eTable). For example, in the group of children and adolescents from low-SES families, one sees an increase in the prevalence of overweight. Whereas a total of 20.0% (95% CI: [18.0; 22.1]) of children and adolescents with low SES were overweight in the 2003–2006 period, this percentage rose to 25.5% (95% CI: [20.5; 31.2]) in the 2014–2017 period (p-value: 0.043). For boys and girls with middle and high SES, there were signs of a decline in prevalence, but this was not statistically significant. The prevalence of obesity is comparatively stable over time in all SES groups, pointing to a slight decline only in the middle SES group (Figure, eTable).

Figure

Prevalence of FIGURE overweight and obesity according to socioeconomic status (SES) and time period among 3- to 17-year-olds in Germany

The SII shows that the prevalence of overweight in the period 2003–2006 in children and adolescents with the lowest SES was 11 percentage points higher compared to that of their peers with the highest SES (Table 3). This difference rose to 19 percentage points in 2014–2017. On the relative scale of the RII, one sees in the first period a 2.1-fold higher risk for overweight in children and adolescents with the lowest SES compared to their peers with the highest SES. By the 2014–2017 period, this risk had increased to 3.7-fold. The magnitude of social differences in the prevalence of obesity does not indicate any significant changes over time.

Table 3

Absolute and relative differences in the prevalence of overweight and obesity among 3- to 17-year-olds in Germany

Discussion

The data from the KiGGS study have made it possible for the first time to analyze secular trends in the socially unequal distribution of overweight and obesity in childhood and adolescence based on German nationwide examination data. Since the baseline survey in the 2003–2006 period, the KiGGS data show strongly pronounced social gradients in the distribution of overweight and obesity to the detriment of boys and girls of low SES. The trend results indicate that the prevalence of obesity in children and adolescents growing up in low-SES families has continued to increase over time. This trend cannot be seen for those growing up in middle and high SES families. Over the course of this development, the social differences in the prevalence of obesity in childhood and adolescence have further widened. The prevalence of obesity as well as the related social differences remained comparatively constant over the period under consideration.

The results presented here are partially in line with international findings. In their systematic review, Chung et al. outline overall trends towards stagnation and widening of socioeconomic differences in the prevalence of overweight and obesity in economically better-off countries (2). According to their review, studies conducted prior to 2000 show primarily an increase in the prevalence of overweight and obesity in all socioeconomic groups, whereas after 2000, fewer than 10% of studies report an increase in overweight and obesity in high-SES groups and almost one third of studies report an increase in low-SES groups. The international comparative HBSC study reveals persistent socioeconomic differences in the prevalence of obesity in 16 European countries, including Germany, while these are increasing in Belgium and Iceland and decreasing in Ukraine (28).

Regarding adulthood, data from Germany and other European countries show a widening of socioeconomic differences in obesity prevalence since the early 1990s (29, 30). In terms of the socioeconomic inequalities themselves, data from Germany indicate that, for example, there has been an above-average increase in the risk of poverty among children and adolescents compared to the overall population during the observation period, that is to say, since approximately the start of the 2000s (31).

In addition to the strengths of this study, which lie mainly in the nationwide population-based random sample, the collection of anthropometric measurement data, and the comprehensive measurement of SES, a number of limitations need to be mentioned. On the one hand, for the time being, the KiGGS examination data enabled only a comparison of two measurement periods, which precluded an analysis of the trend curve, that is, whether there is a secular trend with a linear or curvilinear pattern of progression. On the other, one needs to bear in mind that the survey periods were prior to the coronavirus pandemic, which is why they relate exclusively to the pre-pandemic period. Closures of schools as well as leisure and sport centers to control the pandemic is likely, at times, to have significantly limited young people’s opportunities for physical activity, especially of those in socially disadvantaged families (32). Thus, the trends observed in the KiGGS data may have further intensified since 2020, and this will need to be investigated in future studies. The prevalence estimates presented here indicate a trend towards a decline in overweight and obesity in higher SES groups. Future studies should continue to consider this trend during and after the pandemic. A further limitation lies in the fact that the sample in which the BMI measurement data was collected was significantly smaller in the KiGGS second wave compared to the baseline survey. Due to this sample size, it was not possible to additionally differentiate SES-specific trends according to different age groups or developmental stages (for example, pre-school age, primary school age, early and late adolescence).

High body weight at a young age often persists into adulthood. For example, obese children and adolescents are five times more likely to be obese in adulthood compared to their non-obese peers (33). Therefore, from a public health perspective, there is a particular need for overweight prevention measures starting at an early age.

International systematic review articles suggest that interventions focusing purely on information transfer and individual behavioral change have little or only short-term success in low-SES groups (34, 35). In these review articles, community-based interventions aimed at structural changes in the living environment of socioeconomically disadvantaged individuals proved to be more effective and have longer-lasting effects. For children, there was evidence of effectiveness for school-based and environmental interventions, as well as for community-based empowerment interventions aimed at putting communities in the position to develop their own solutions to promote physical activity and healthy eating (35). According to international evidence, interventions on the societal level such as taxation measures (for example, taxing sugar-sweetened beverages) also have potential to reduce socioeconomic differences in body weight (36, 37). In Germany, according to the coalition agreement of the current federal government of 2021, there are plans, for example, to set up quality standards for healthy food in school canteens as well as to ban advertising of foods with high sugar, fat, and salt content targeted at children.

As a whole, the results of the KiGGS study demonstrate that the inequality in the distribution of overweight among young people in Germany that was already very pronounced at the beginning of the 2000s has further worsened—to the detriment of those with low SES. Structural prevention that takes into account the living environment of young people in socioeconomically disadvantaged conditions is of major importance in order to tackle this trend.

Acknowledgments

The authors would like to thank PD Dr. Thomas Lampert (†) and Dr. Benjamin Kuntz for their suggestions and comments on an earlier version of this analysis.

Funding

The KiGGS study was financed by the German Federal Ministry of Health (Bundesminsterium für Gesundheit) (KiGGS baseline survey and KiGGS second wave) and by the German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung) (KiGGS baseline survey).

Conflict of interest statement
Dr. Hoebel is co-speaker of the Joint Working Group “Sozialepidemiologie” (social epidemiology) of the Germany Society of Medical Sociology (Deutsche Gesellschaft für Medizinische Soziologie, DGMS), the German Society for Social Medicine and Prevention (Deutsche Gesellschaft für Sozialmedizin und Prävention, DGSMP), and the German Society for Epidemiology (Deutsche Gesellschaft für Epidemiologie, DGEpi).

The remaining authors declare that no conflict of interest exists.

Manuscript received on 6 May 2022, revised version accepted on 19 September 2022.

Translated from the original German by Christine Rye.

Corresponding author
Dr. Jens Hoebel
Fachgebiet Soziale Determinanten der Gesundheit
Abteilung für Epidemiologie und Gesundheitsmonitoring
Robert Koch-Institut
General-Pape-Str. 62–66, 12101 Berlin, Germany

Cite this as
Hoebel J, Waldhauer J, Blume M, Schienkiewitz A:
Socioeconomic status, overweight, and obesity in childhood and adolescence—secular trends from the nationwide German KiGGS study.
Dtsch Arztebl Int 2022; 119: 839–45. DOI: 10.3238/arztebl.m2022.0326

►Supplementary material

eReferences, eMethods, eTable:
www.aerzteblatt-international.de/m2022.0326

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