Analyzing the distinguishing factors that affect childhood obesity in South Korea

Abstract

Understanding obesity in children is crucial because it can lead to adulthood obesity and result in fatal chronic diseases. Distinctive factors associated with obesity in adults have been described, but distinctive factors related to children remain unclear. We analyzed the correlation between the percentage of body mass index and lifestyle habits by conducting surveys on physical, nutritional, and psychological factors, and we used annual physical examination data to compare different traits among elementary school students (n = 197) and middle school students (n = 461). Our study revealed that the computing hours in elementary school students with overweight and obesity were significantly correlated with the percentage of body mass index (r = 0.29 on school days and r = 0.35 on days off, all P<0.05). No statistically significant difference was found (all P>0.05) in the computing hours of middle school students with overweight and obesity. Childhood obesity can cause depression and reduce children’s quality of life because of their distorted body perception. In conclusion, physical factors directly affecting childhood obesity and psychological and environmental factors surrounding a child should be considered.

Keywords

screen time / quality of life / eating habits / childhood obesity / percentage of body mass index

1 Introduction

Obesity is defined as a state of abnormal or excessive fat accumulation in the body [1]. It is known as a risk factor of chronic diseases, such as diabetes [2], hypertension [3], and hyperlipidemia [4], and it leads to an increased risk of cardiovascular diseases, such as cerebral and myocardial infarctions [5]. According to the World Health Organization’s global obesity prevalence statistics [6], more than 190 000 adults (39% of the world’s population) were overweight in 2014, and 600 million adults (13% of the world’s population) were obese. In particular, obesity is more problematic among adolescents than among adults because of the high morbidity rate of adulthood obesity; the number of children with obesity in developing countries is estimated to be 7.5 million to 15.5 million, and more than half of them lived in Asia in 2014 [7]. This fact suggests that obesity in Asian children is serious and can cause social problems.

Improving lifestyles, such as eating habits and exercise, is one of the most important measures to effectively prevent childhood obesity [8]. Thus, an individual’s daily life pattern and physical ability should be understood. The management of personal habits and various psychological and social causes that may appear during the growth period should be integrated and managed. Subjective feelings about one’s body shape can cause psychological problems, such as depression and anxiety, which can be related to childhood obesity [9]. These psychological problems can occur more frequently during childhood obesity [10]. Studies have been conducted to explore various factors that measure physical abilities and solve childhood obesity. For example, if muscle mass is high, athletic ability is expected to improve [11]. Conversely, physical ability decreases when fat mass is high [12].

Obesity in children and adolescents should be accurately characterized, and their life patterns should be identified in terms of everyday life habits in an integrated manner. However, in comparison with adulthood obesity, childhood obesity and its related factors, including the physical ability of children with obesity, psychological causes, and children’s life patterns, have yet to be fully elucidated. Thus, this study aimed to investigate the differences in the physical ability, psychological stability, and lifestyle among elementary and middle school students with obesity and normal weight in South Korea. Prevention and management programs for childhood obesity can be developed on the basis of these differences.

2 Materials and methods

2.1 Study population

This study was conducted in Chungju City, South Korea. Chungju is a city inhabited by more than 200 000 people and located approximately 150 km from Seoul, South Korea [13]. This study was planned for young people aged 9–13 years and living in Chungju. A letter about their participation in this study was sent to the elementary school and junior high school administrations in Chungju. The official documents were provided by the Chungju City Office and the Chungju City Education and Support Office. A letter, with the study protocol attached, was sent to 54 schools in Chungju, and 6 schools consented to participate in this study. Finally, 3 elementary schools and 2 middle schools were enrolled. Male students in the 4th grade in the elementary schools (aged 9–10 years) and the middle school 7th graders (aged 12–13 years) were mainly analyzed.

2.2 Study design

In South Korea, the physical activity promotion system (PAPS) is mandatory every year from the fifth grade of elementary school to the third grade of high school [14]. In our study, the physique and physical fitness of the students were evaluated on the basis of PAPS, and additional surveys were conducted. The additional questionnaire for each student consisted of a physical activity survey, psychological survey (body image, self-esteem, depression, and quality of life[QOL]), and nutritional survey (a frequency of food consumption survey, eating habits survey, and nutritional knowledge survey). The questionnaire for the students was completed under the direction of the school guidance teacher.

2.3 Baseline characteristics

A total of 677 students (203 elementary school students and 474 middle school students) participated in the study. The data from 6 elementary school students and 13 middle school students were not included because of the omission of questionnaire data. Finally, 197 elementary school students and 461 middle school students were included in the study (response rate= 97.2%, 658/677) (Table 1). The prevalences of overweight–obesity (85%≤p-BMI) were 33.5% (66/197) in the elementary school students and 28.0% (129/461) in the middle school students. The average age of the elementary school students was 9±1 years in the normal weight group and the overweight–obese group, and the average age of the middle school students was 12±1 years in the normal weight group and the overweight–obese group under the category of p-BMI. The BMIs were 17.1±1.8 kg/m² in the normal weight group of the elementary school students and 24.0±2.6 kg/m² in the overweight–obese group of elementary school students. The middle school student’s BMIs were 19.2±2.2 kg/m² and 26.9±2.8 kg/m² in the normal weight and overweight–obese groups, respectively. The z-scores were analyzed for normal weight and overweight–obesity in the following order: −0.3±0.7 and 1.7±0.4 (elementary students) and −0.2±0.7 and 1.7±0.5 (middle school students). The percentages of fat were 9.0%±4.8% and 22.8%±4.3% for the normal weight group and the overweight–obese group among the elementary students, respectively, and 11.8%±5.7% and 27.4%±3.8% for the normal weight group and the overweight–obese group among the middle school students, respectively. The following values of fat mass were obtained: 3.0±1.9 kg (elementary school normal weight group), 11.3±4.3 kg (elementary school overweight–obese group), 6.0±3.6 kg (middle school normal weight group), and 19.4±5.2 kg (middle school overweight–obese group). The following values of muscle mass were determined: 27.0±3.0 kg (elementary school normal weight group), 34.3±4.1 kg (elementary school overweight–obese group), 39.4±5.3 kg (middle school normal weight group), and 46.3±5.4 kg (middle school overweight–obese group). The baseline analysis of the groups was based on p-BMI, and the general morphology between the normal weight and overweight–obese groups was significantly different (P< 0.001), but no difference was found in terms of age (P= 0.28 elementary school students; P = 0.44 middle school students).

2.4 Physical examination

Age, body mass index (BMI), percentage of BMI (p-BMI) (%), z-score, percentage of fat (%), fat mass (kg), and muscle mass (kg) were based on the results of the PAPS. Obesity in children and adolescents leading to adult obesity differs, but its incidence is increasing, and the rate of growth depends on gender and age. Therefore, BMI-for-age, which is referred to as “p-BMI” in this paper, was used to determine obesity. p-BMIs of over 85% and over 95% indicated overweight and obesity, respectively [15].

Five physical examinations were conducted and expressed using a total of 20 points: progressive aerobic cardiovascular endurance run (PACER) score, flexibility score, grip strength score, jumping score, body fat (BMI using height and weight), and comprehensive physical ability score (with a final score of 100).The physical examination score (total) was calculated on the basis of these examinations. The higher the score was, the better the physical ability would be.

The PACER score (running around) was based on running 15 m length for elementary school students and 20 m length for junior high school students for about 10 min. The flexibility score was measured using a left ankle meter for about 30 s while the upper body was bent forward. The grip strength score was measured using a dynamometer on the left and right sides for 2 min. To measure the jumping score, we conducted a long jump for about 30 s by using an automatic meter. The percentage of body fat was determined using automatic body fat measurement equipment (IOI 353 analyzer; Jawon Medical, Seoul, South Korea) while wearing light clothes and no shoes via bioelectrical impedance analysis. The measurements were taken in the following order: physical measurement (height and weight), body fat measurement, flexibility test, jumping test, grip strength, and PACER. Waist circumference was measured from the lateral side of the ribs to the midpoint between the top of the iliac crest of the child, and this procedure was performed behind a black curtain for privacy. The blood pressure (systolic and diastolic) of the children in a stable state was measured by a registered nurse. Children were divided into obesity groups based on p-BMI because of the large variation in BMI according to gender and age [16]. In particular, the children were divided into two groups, namely, normal weight (5%≤p-BMI<85%) and overweight–obese (p-BMI≥85%).

2.5 Physical activity questionnaire

The questionnaire items about obesity in pediatric adolescents were developed on the basis of the questionnaires used by the Korean Society for the Study of Obesity. To focus on the children’s environmental factors, we considered the following variables to determine their correlation with obesity: the amount of time spent watching TV or videos during the day (school day/day off) and the average sleeping time.

2.6 Nutritional habit questionnaire

The questionnaire items regarding nutritional habits were taken from the questionnaire used by the Korean Society for the Study of Obesity. We focused on the correlation of eating habits with being overweight and obese. Therefore, we analyzed the correlation between the degree of obesity and various eating habits, such as number of times of eating breakfast (per week), regularity of eating (three regular meals a day), frequency of eating out, and good knowledge of nutrition.

2.7 Psychological questionnaire

The psychological questionnaire consisted of items about body image, self-esteem, depression, and QOL. The body image scale was composed of not only contents about appearance evaluation and appearance orientation but also various items about body ego as described by Cash in 1990 [17], Cho in 2001 [18], and Lee in 2003 [19]. The scale consisted of 13 items, with four points per item (52 points in total). The higher the score was, the more positive the image of the body and the more appearance-oriented the individual would be. This questionnaire comprised “appearance evaluation,” which determined whether the self-portrait of their body was positive or negative (e.g., “I think that I am physically attractive”), and “appearance orientation,” which defined their effort to maintain and improve their appearance by evaluating their activeness in managing their body to be in a good shape. The higher the score was, the more positive the attitude toward their body would be. They would also be highly appearance oriented.

Self-esteem was measured using the Korean version in 1974 [20] of the self-esteem scale originally developed by Rosenberg in 1965 [21]. The scale was used to assess positive self-esteem (five items) and negative self-esteem (five items). The higher the score was, the higher the self-esteem would be. Depression was assessed using the depression and anxiety scale of the youth self-report scale (Korean version) based on the youth self-report scale [22] produced by Achenback in1991 (score range 0–32). The higher the score was, the higher the degree of depression and anxiety would be. To measure the QOL, we used PedsQL 4.0 Generic Core Scales [23], which has a Korean version in 2004 [24]. The QOL included physical function, symptoms related to disease and treatment, psychological function, social function, cognitive function, and academic function. The tool was designed to be suitable for use by children and adolescents in the community [25]. The higher the score was, the better the QOL would be [26].

2.8 Privacy protection

This study involved children under 18 years of age. In addition to the children’s consent, written consent was obtained from one of their parents. In case of unacceptable parental consent, that is, if it was unavailable, or the place of residence was different, a legal representative or grandparents gave their consent. This study was approved by the International Review Board of the Catholic University of Korea.

2.9 Statistical analysis

For continuous variables, the mean±standard deviation (SD) was used for the analysis. For categorical variables, the percentage (%) was employed. Student’s t-test or chi-square test was conducted to clarify the differences in the baseline between the two groups (normal weight group and overweight–obese group in elementary and middle schools). Subgroup analysis was conducted using p-BMI. Pearson’s correlation analysis was performed to demonstrate the relation between p-BMI and physical tests (examination and questionnaire), nutritional habits, and psychological variables. Data were examined using SPSS (PASW Statistics for Windows version 18.0; SPSS Inc., Chicago, IL, USA) and considered significant if the significance level was less than 0.05.

3 Results

3.1 Physical examination comparison between children with normal weight and overweight–obesity

The physical examination score of the overweight–obese group was significantly lower than that of the normal weight group (Fig. 1). The total physical examination score was higher in the normal weight group than in the overweight–obese group of the elementary school students (49.4±12.5 [normal weight group] vs. 33.0±10.8 [overweight–obese group], P<0.001) and the middle school students (53.2±12.8 [normal weight group] vs. 33.3±11.3 [overweight–obese group], P<0.001). The PACER score was significantly higher in the normal weight group than in the overweight–obese group of the elementary school students (12.2±4.7 [normal weight group] vs. 6.9±3.7 [overweight–obese group], P<0.001) and the middle school students (9.6±4.8 [normal weight group] vs. 4.0±2.8 [overweight–obese group], P<0.001). No statistically significant difference was found in the flexibility score between the overweight–obese group and the normal weight group in the elementary school students (7.5±6.0 [normal weight group] vs. 6.8±5.8 [overweight–obese group], P = 0.37). This result was also observed in the middle school students (10.8±5.2 [normal weight group] vs. 9.9±5.3 [overweight–obese group], P = 0.091). The grip strength score was significantly higher in the students with obesity and the elementary school students (6.4±3.2 vs. 8.7±3.4, P<0.001, 8.3±3.4 vs. 9.5±3.1, P = 0.001) than in the other groups. On the contrary, the jumping score was significantly lower in the overweight–obese group than in the normal weight group of the elementary school students (10.3±3.9 [normal weight group] vs. 7.2±3.1 [overweight–obese group], P<0.001) and the middle school students (11.2±3.9 [normal weight group] vs. 6.7±3.8 [overweight–obese group], P<0.001).

3.2 Psychological questionnaire comparison between children with normal weight and overweight–obesity

Among the elementary school students, body image (27.6±4.8 [normal weight group] vs. 27.7±6.6 [overweight–obese group], P = 0.85) and depression (3.7±4.6 [normal weight group] vs. 4.4±5.4 [overweight–obese group], P = 0.40) were higher in the overweight–obese group than in the normal weight group. By contrast, self-esteem (31.2±4.9 [normal weight group] vs. 29.9±5.7 [overweight–obese group], P = 0.09) was lower in the overweight–obese group than in the normal weight group (Fig. 2). The same result was shown in the middle school students. The QOL score was significantly higher in the normal weight group than in the overweight–obesity group of the elementary school students (81.9±11.3 [normal weight group] vs. 76.2±14.6 [overweight–obese group], P = 0.006) and middle school students (78.4±11.5 [normal weight group] vs. 74.0±13.6 [overweight–obese group], P = 0.001).

3.3 Factors affecting p-BMI

Waist circumference was positively correlated with p-BMI regardless of the obesity level (P<0.001) in the elementary and middle school students (Table 2). Body self-perception was positively correlated with p-BMI in the normal and obese groups of the elementary and middle school students (P<0.005). The effort to lose weight (in the past year) was negatively correlated with p-BMI in the elementary and middle school students and was statistically significant, especially in the middle school students (P<0.01). The time spent watching TV by elementary school students was positively correlated with obesity, but it was not statistically significant, indicating a trend similar to that of the middle school students. However, the computing hours in the elementary school students were significantly correlated with obesity (r = 0.29, P<0.05 on school days and r = 0.35 and P<0.01 on days off). The time spent on the computer by middle school students was negatively correlated with obesity, but no significant difference was found (r = −0.14 and P = 0.12 on school days and r = −0.11 and P = 0.26 on days off).

In the case of the desire to exercise, the higher the score was, the lower the level of desire would be. A positive correlation was observed among elementary and middle school students, and the correlation coefficient of the children with obesity was higher than that of the children with normal weight (P = 0.03 and P = 0.02 in the elementary and middle school students, respectively), which was significant in the overweight–obesity group (r = 0.28 elementary school students; 0.22 middle school students). In other words, the higher the degree of obesity was, the lower the level of desire would be.

The characteristics that showed a positive correlation with p-BMI included the average sleep hours (in all of the groups except the normal weight group of the middle school students), the habit of eating breakfast (in overweight–obese group of the middle school students), and the score of nutritional knowledge (the middle school normal group), but no statistical significance was found in any of them except the score of nutritional knowledge among the normal group of middle school students.

Regarding the psychological status of a child, the four psychological surveys (body image, self-esteem, depression, and QOL) were negatively correlated with p-BMI in the overweight–obese group in the elementary school students (r = −0.33, P<0.01), but a stronger negative correlation was found in the overweight–obese group of middle school students (r = −0.06 in the normal weight group and r = −0.08 in the overweight–obese group). In terms of body image, a positive correlation was found in the normal weight group of elementary school students, and a positive correlation was found in the overweight–obese group (r = −0.02 and P = 0.80 in the normal weight group, r = 0.10 and P = 0.44 in the overweight–obese group). By contrast, a strong correlation was observed in the overweight–obesity group of the middle school students (r = 0.08 and P = 0.13 in the normal weight group, r = 0.11 and P = 0.21 in the overweight and obese group). Depression was also positively correlated (r = 0.32 and P<0.01) in the elementary school overweight–obesity group, and the QOL was negatively correlated with p-BMI (r = 0.39, P<0.01). No significant correlation was found between depression and obesity in middle school students. In terms of QOL, a high negative correlation was found in the overweight–obesity group, but it was not statistically significant (r = −0.06 and P = 0.31 in the normal weight group, r = −0.12 and P = 0.20 in the overweight and obese group).

4 Discussion

Childhood obesity often progresses to adulthood obesity [27]. As such, obesity management should begin from childhood. In this study, the respective rates of obesity in elementary school students and middle school students in 2014 were 33% and 28%, which was considerably higher than that of American boys (20%) [28] in 2010. The fat mass (kg) and percentage of fat (%) of children with obesity were higher than those of children with normal weight. In particular, the percentage of fat increased in middle school students, and active management, such as education about a healthy lifestyle to prevent obesity in children, is necessary from elementary school onward. Overall, the physical abilities of children with obesity in terms of PACER, flexibility, jumping, and total physical examination score were lower than those of children with normal weight. Conversely, the grip strength of the former was higher than that of the latter. Ultimately, efforts to reducing the percentage of fat in the children with obesity and improving their physical abilities should be emphasized and taught during childhood. Thus, the rate of obesity decreases in adulthood, and the prevalence of chronic or cardiovascular diseases becomes reduced [29].

Elementary and middle school students are sensitive about their appearance, and they often feel that they appear obese or perceive themselves negatively [30]. Even though these students are not actually obese, they often feel obese [31]. In particular, female high school students likely compare their appearance with students in other groups, followed by female middle school students, male high school students, and male middle school students [32]. In this study, body image was not different between boys with normal weight and obesity; as such, male students seem to be less interested in their appearance than female students [33].

Depression was higher in children with obesity than in children with normal weight, and the QOL was significantly lower in the overweight–obese group than in the normal weight group. The misinterpretation of body image also tends to increase depressive symptoms [34]. In the present study, no difference was found in body image, and the tendency of children with obesity had a higher tendency to be depressed; thus, the QOL was not significantly different. Other factors besides body image seems to may have affected the children’s depression. Although the results were not statistically significant, the combination of various minor causes, such as low self-esteem and depression related to childhood obesity, might negatively affect the QOL of the children. In the case of boys, body image and other psychological variables should be separately considered, and further research should be conducted. We speculated that children’s distorted body image and negative perception of themselves could have had a negative impact on the QOL. Children undergo the sensitive process of puberty and are heavily influenced by mass media. As such, the self-esteem and depression scores might become negative in children with overweight–obesity, which might decrease the overall QOL, could lead to a passive childhood, and might negatively influence the child’s health in terms of obesity.

On average, the number of study hours differed between elementary school and middle school students [35]. In terms of school study time, elementary school students have more spare time than middle school students. Elementary school students with obesity tended to spend their free time on a computer. Middle school students lacked leisure time compared with elementary school students. Therefore, the correlation with screen time, such as watching TV or using a computer, was not significant.

Two solutions are developed to address obesity-related problems, especially in elementary and middle school students. Instead of allowing elementary school students to focus on screen time, they should be encouraged to engage in exercise, such as participating in public gymnastic classes and interesting physical games. With this method, elementary and middle school students can overcome childhood obesity. Considering that middle school students have less spare time, healthcare providers should focus on external factors, such as food preferences, instead of screen time to prevent childhood obesity. With the widespread use of smartphones and the internet, elementary and middle school children have more screen time (watching TV and looking at computers) than before [36], resulting in a decrease in physical activity. After becoming an adult, children likely develop metabolic syndromes, such as hypertension and diabetes, [37]. Increased screen time is also known to increase the risk of cardiovascular disease because of sedentary lifestyle [38]. This study also illustrated that children who were overweight or obese were more likely to concentrate on the computer in elementary school than those who were not obese. Time spent on watching TV was longer in the overweight–obese group than in the normal weight group, although the difference was not statistically significant. Spending long hours in front of a TV can negatively affect self-esteem and depression from the distorted body image portrayed on TV or computers [39], which can have a considerable impact on the general QOL of children. Therefore, new approaches to increase physical activity and psychological interventions for the use of TVs, computers, and other devices, which are stimulant mediators, should be developed to find solutions that can be easily accessed and maintained by children with obesity. More active and realistic interventions should be provided to ensure that healthy habits and psychological foundations are well established in school-based group life. Therefore, children with obesity should be encouraged to increase the amount of time that they spend on physical activity rather than on TV or computers.

The following limitations of this study should be noted. First, we did not use objective laboratory scores. If we analyzed the data with laboratory tests, we could objectively confirm the physical condition of children. Second, we measured the dietary behavior and various exercise tendencies by using a 24-hour recall memory format; thus, we relied solely on the memory of the children and the parents. Third, this study targeted only boys, and all of the schools are located in one area (Chungju City). As such, selection bias possibly occurred to some extent, and our findings could not be generalized to all of the children in terms of obesity in South Korea.

5 Conclusions

In this study, the physical, psychological, and lifestyle habits of normal weight and overweight–obesity groups of elementary and middle school students were examined comprehensively and systematically. In particular, this study investigated the lifestyle related to childhood obesity, reflecting the students’ behavior on school days and days off. This study is noteworthy because specialists managing the physical fitness of children can have access to derived characteristics that can be considered in an intervention for children and adolescents. This study will contribute to the management and prevention of child obesity if psychological aspect and physical intervention for a large number of children are further reinforced, and a lifestyle management program is introduced.

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