Background
The epidemic of obesity in every segment of the population is a serious public health problem in the high-income as well as low- and middle-income countries of the world [
1‐
3]. The prevalence of obesity is generally lower but is increasing faster in low- and middle-income countries than in high-income countries [
4,
5], but the evidence from, for example, the former Communist Bloc countries in Europe is still limited [
6]. On the evidence of the existing prevalence and trend data [
1,
7‐
9] and the epidemiological evidence linking obesity with long-term cardiovascular, metabolic, and other health consequences [
10], it is necessary to describe obesity as a public health crisis with serious negative impacts on the quality of life of people and imposing a considerable burden on national health-care budgets [
11,
12].
To simplify, obesity is the result of a long-term positive energy balance between food intake and expenditure, with its rate being mediated by the complex interaction of multiple behavioural, biological, and environmental factors [
13‐
16]. Lifestyle behaviour is strongly associated with obesity in school-aged children, regardless of country or continent [
13,
15,
16]. Everyday physical activity of moderate-to-vigorous intensity (MVPA) and longer sleep duration have been associated with lower odds of overweight or obesity in school-aged children [
16], while shorter sleep duration and longer outside-of-school screen time (ST – watching television and playing video/computer games) have been associated with higher odds of obesity [
15,
16]. The consumption of sugar-sweetened beverages as an example of unhealthy food intake has been shown to be one of the key contributors to the risk of child overweight/obesity [
17]. Although the consumption of sugar-sweetened beverages has declined over the last 15 years, it is still high among children and adolescents, with a negative impact on health – a higher incidence of obesity, insulin resistance, and dental caries [
17]. Many of the energy balance-related behaviours in children and young people vary considerably with regard to the socio-economic status (SES) of their families [
6,
16,
18,
19].
One of the major social determinants of child and adolescent obesity is the SES of their families [
7,
9,
20]. Only a few of the trend-related publications that exist reveal a growing socioeconomic gradient in high-income countries – a stabilized or slight decreasing trend in the prevalence of obesity in children and adolescents from high-SES families, as opposed to a steady increase in the prevalence of obesity among their peers from low-SES families [7, 9,20]. Between 2003 and 2014, active participation in the Special Supplemental Nutrition Program for Women, Infants, and Children in Los Angeles [
20] was first accompanied by an increase in childhood obesity (2003–2005), followed by a stagnation of obesity (2005–2010), and then a final decline in childhood obesity (2010–2014), with significant differences between children from different SES backgrounds. In most years, the incidence of childhood obesity was highest in the families with the lowest SES [
20]. Bann et al. [
21] point to a diametric change in the relationship between SES and body weight in a longitudinal survey. In the cohorts before 2001, lower SES was associated with lower weight and inequalities did not differ systematically with age until the 2001 cohort, in which weight and BMI inequalities widened at older ages. Nevertheless, critical information gaps persist in relation to the impact of childhood and life course SES on obesity in low- and middle-income countries [
22], as well as an analysis of the impact of health-related programmes on the prevalence of obesity regarding SES [
5].
Low- and middle-income European countries (including the countries of Central and Southern Europe from the former Communist bloc) appear to tend to replicate the ‘negative’ health-related behaviour patterns – a decrease in MVPA, an increase in ST [
6,
23,
24] – which had previously been reported in high-income countries [
25]. The rapid increase in childhood and adolescent obesity in low- and middle-income countries underlines the fact that these countries have failed to learn from the development of obesity in high-income countries. Czechia is one of the most economically developed European countries in the former Communist bloc [
26]. Since 2006, it has been implementing a number of national health-related and sports programmes (such as “The Olympic Flag of Versatility”, “School Fruit and Vegetable Scheme “, and “School Milk Scheme”) for children and adolescents, supported by the Ministry of Education, Youth, and Sports [
27]. However, the effect of these programmes on the health and health-related behaviour of children and adolescents is not monitored and evaluated to an adequate extent.
The present study attempts to bridge the gap between the national health-related and sports programmes that have been implemented and the lack of evidence of their effectiveness in terms of their potential impact on the prevalence of obesity. Therefore, the main objective of the study is to analyse the changes in the prevalence of obesity among Czech adolescents between 2002 and 2018 with regard to the SES of adolescents’ families and to find SES-separated correlates of adolescents’ obesity in 2018.
Discussion
The key findings of the trend analysis between 2002 and 2018 include the revelation of an ‘up-stairs’ effect in the prevalence of obesity in all adolescents except for girls from the high-SES category and increasing differences in the prevalence of obesity between gender-separated low- and high-SES categories of adolescents.
Czechia has undergone rapid economic development and is one of the most economically developed countries in Central and Eastern Europe [
26,
45]. This rapid economic development was reflected in the growth of families with high SES after 2010.
However, as in high- economic developed countries, rapid economic development is not always accompanied by positive health development of adolescents in all SES categories. It turns out that Czechia is repeating a similar development in child and adolescent obesity to economically more advanced countries (e.g. Australia, England, France, Germany, Netherlands, and the USA) 10–15 years ago, where the increase in obesity reached a plateau, with a subsequent increase in obesity among low-SES adolescents [
7,
63].
After a sharp increase in obesity among Czech adolescents between 2002 and 2006, a number of national health-related and sports programmes (such as “The Olympic Flag of Versatility”, “Fruit and Vegetables in Schools”, and “Milk to Schools”) were introduced for children and adolescents with support from the Ministry of Education, Youth, and Sports [
27]. A new compulsory subject called “Health Education” was also established at primary schools. This course focuses on healthy eating habits, non-risky behaviour (avoidance of drug use and smoking) and nature and environmental friendliness. These health-promoting activities may have contributed to the stabilization (plateau) of the prevalence of overweight/obesity among adolescents between 2006 and 2014.
However, following the reduction of nationwide financial support for some national programmes between 2013 and 2015 due to different government priorities, a rebound of overweight/obesity among adolescents was registered in the 2018 national data collection. The subsequent increase in overweight/obesity is most pronounced in adolescents with a low-SES background. The possible subsequent effect of national health and sport programmes is most noticeable in adolescents from high-SES families. In addition, significantly higher odds of obesity in the age categories of 11 and 13 years from low-SES families than among 15-year-olds indicated an expected rise in obesity in older low-SES adolescents in the near future. The trend patterns of excessive body weight, especially obesity in adolescents with a low-SES background and in the youngest age category examined between 2002 and 2018, indicate an urgent need for improvement. An international comparison of obesity changes between 2002 and 2014 across 27 European countries revealed that most market-driven obesity in Eastern European countries, where the levels of obesity were relatively low in 2002 and in adolescents with a low-SES background (6).
Special attention is therefore paid to the subsequent analyses of obesity correlates in adolescents from various SES backgrounds. Despite the differences in SES, three correlates of energy balance-related behaviours were identified as being associated with significantly lower rates of obesity in all SES groups of adolescents: i) regular WVPA (≥4 times a week), ii) active participation in sport, and iii) daily consumption of sweets. Moreover, in adolescents from low- and high-SES families, engagement in MVPA for at least 60 min a day also significantly reduces the risk of obesity. In adolescence, behaviour associated with more pronounced energy expenditure (PA of at least moderate intensity, participation in sport) appears to have a stronger anti-obesity effect than the absence of unhealthy eating habits. However, the energy expenditure required for adolescents must also include the energy required for bodily growth and development. Unlike other studies [
64‐
66], more frequent eating (at least twice a month) in fast food restaurants in Czech adolescents with medium and high SES was associated with a significantly lower risk of obesity than in adolescents with lower rates of eating in fast food restaurants. On the other hand, regular breakfast is, in line with Marlatt et al. [
66], associated with lower rates of obesity. These eating patterns are “more typical” for adolescents who regularly participate in sports than for non-participating adolescents. The participation of 11–15-year-old adolescents in sport was related to more frequent eating at fast food restaurants but less frequent snacking in front of the computer and intake of crisps than in non-sporting participants [
67]. In addition, in the context of TV, it has been found that adolescents who watched TV for a longer time were more likely to consume sweets and soft drinks daily and less likely to consume fruit and vegetables [
56]. However, a more significant obesity-related problem can occur when an adolescent ceases to participate in sports or is not regularly involved in MVPA and does not change his or her eating habits, because unhealthy eating habits adopted in adolescence tend to persist into adulthood and represent a crucial factor in the development of obesity [
68‐
70].
Another explanation for the results that the daily consumption of sweets and eating more frequently in fast food restaurants are related to a lower likelihood of the prevalence of obesity is that non-obese adolescents do not have to care about unhealthy eating habits as much as their obese classmates, as evidenced by previous findings [
71,
72]. Better eating habits in the obese category may have been influenced by the “social desirability” factor in addressing dietary habits in the HBSC questionnaire [
73]. Undervaluation of responses to unhealthy and socially undesirable foods has proved to be commonplace in questionnaire surveys of overweight and obese participants [
74]. The results could also be influenced by the current tendency among overweight or obese adolescents to reduce weight [
75]. Because HBSC is cross sectional it is plausible that obese adolescents may be engaging in dietary restriction/healthier dietary habits at the time of the survey.
Excessive body weight is not only associated with long-term cardiovascular and metabolic health complications [
10], but also with social and psychosomatic complications [
71,
76]. Overweight/obese 11-to-15-year-old girls spend less time with friends after school, and overweight/obese boys report less frequent e-communication compared to normal-weight adolescents. In addition, the overweight/obese weight status of adolescents is associated with not perceiving a best friend as a confidant [
76]. This finding is perhaps also one of the reasons why there are more individuals with normal body weight among the participants in organized team or individual sports. In addition, adolescents from low-SES backgrounds have been significantly more likely to fall behind their peers in terms of life satisfaction [
71]. In addition to the financial and logistical demands of adolescents’ participation in organized leisure-time sport, this finding may contribute to explaining why the lowest proportion of participants in organized sport and regularly engaging in WVPA is among adolescents with low SES.
Although the lowest proportion of participants in sports and regular WVPA implementation is among the low-SES adolescents, at least 60 min of any MVPA daily can assist in reducing obesity. Therefore, in addition to sport, it is necessary to support and create the conditions for daily implementation of MVPA in all children and adolescents, regardless of the SES category. Improving public open spaces in low-SES areas by installing play spaces for recreational PA [
77] or expanding school-related PA (including active recess, physical education lessons [
78,
79] and after-school nursery [
80]) has an impact on increasing day-to-day PA [
80] and reducing children’s obesity [
80,
81].
Short sleep duration is generally associated with increased obesity in European adolescents [
82] as well as in adolescents from Canada and the United States [
83,
84]. In addition, a positive relationship between shorter sleep duration and obesity appears to be related to both sides of energy balance-related behaviours as a result of a combination of increased food intake and more sedentary habits [
82]. However, in our study, short sleep duration at weekends is associated with a significantly higher risk of obesity only in adolescents from medium and high SES backgrounds. A higher prevalence of obesity also appears to be related to the environments that children and adolescents reside in and in the neighbourhood of the schools they attend [
65]. Fast food restaurants are more frequently present in low-SES neighbourhoods [
19,
65]. The availability of fast food restaurants near the place of residence or schools is associated with lower consumption of fruits and vegetables, higher consumption of soft drinks, and increased odds of childhood obesity being diagnosed [
65].
Strengths and limitations
The large sample size, with high response rates in all the survey cycles, strict adherence to the international standardized questionnaire and research protocol, and the same well-trained research team responsible for data collection are major strengths of this study.
The primary limitation of this study is that the data is based on self-reported assessment. However, the self-reported measures of body weight and height have been validated, and other studies have revealed high correlations between self-reported and laboratory measurements of BMI, making it suitable for epidemiological studies to identify excessive body weight in children and adolescents [
36]. Although every attempt was made to minimize bias, the self-reported measures applied in this study are subject to recall and social desirability bias, which may have affected the responses. The cross-sectional design of this study does not allow us to interpret the results on the relationship between responses and explanatory variables causally. However, previous longitudinal studies point to the beneficial effects of additional school physical activity on reducing obesity in school-age children [
80,
81].
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