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Publicly Available Published by De Gruyter December 8, 2021

Weight changes of children in 1 year during COVID-19 pandemic

Si-Hwa Gwag ORCID logo, Ye Rim Oh ORCID logo, Jae Wook Ha, Eungu Kang, Hyo-Kyoung Nam ORCID logo, Yoon Lee ORCID logo, Young-Jun Rhie ORCID logo and Kee-Hyoung Lee ORCID logo

Abstract

Introduction

The coronavirus disease 2019 (COVID-19) pandemic has changed everyday life. The Korean government urged schools to close as a measure of social distancing, and children and adolescents seemed to gain weight due to home confinement. We aimed to investigate the trends in weight changes in children during the pandemic period.

Materials and Methods

This retrospective study included 139 children aged between 6 and 12 years who visited the pediatric endocrine clinic for regular growth follow-up for 1 year during the COVID-19 pandemic. We analyzed changes in the body mass index (BMI), BMI z-score, and proportion of children who were overweight or obese over a period of 1 year.

Results

The BMI and BMI z-scores of the 139 children increased significantly over the year. The increase was maximum during the first three months of the COVID-19 pandemic, with little change between the third and sixth month of the pandemic. The proportion of children who were overweight or obese increased over time, from 24.5% at the COVID-19 pandemic baseline to 38.1% 1 year later (p < 0.001).

Conclusions

The COVID-19-related lockdown resulted in significant weight gain in Korean children. Changes in BMI showed different trends depending on the degree of school closure. An overall shift from normal weight to overweight or obesity was observed during the pandemic period.

Introduction

Childhood obesity is a serious health concern worldwide. Obesity has a complex etiology involving environmental and genetic components [1, 2]. Increasing trends in childhood obesity are correlated with an increased intake of high-calorie diets, as well as a sedentary lifestyle, including physical inactivity and excessive screen time. The prevalence of obesity-related diseases, such as non-alcoholic fatty liver disease, diabetes mellitus, and cardiovascular disease, in children and adolescents has increased notably in recent decades [3], [4], [5]. Childhood-onset obesity frequently extends into adulthood; therefore, it is associated with long-term morbidity and mortality [6].

In December 2019, a novel coronavirus from China spread globally to cause what is now known as the coronavirus disease 2019 (COVID-19) [7]. On March 11, 2020, the World Health Organization (WHO) declared this global emergency the COVID-19 pandemic [8]. Many countries have adopted the “lockdown” strategy as a means to avoid crowding. The Korea Disease Control and Prevention Agency implemented “social distancing” to prevent disease transmission [9].

Measures of lockdown during the COVID-19 pandemic induced a tremendous change in lifestyle behaviors [10], [11], [12], [13], [14]. The Korean government decided to delay the opening of schools after the winter break. Schools were completely closed for approximately three months after the initiation of social distancing. Children were forced to take online classes as substitutes for offline classes, avoid outdoor activities, and spend more time at home. From May 20, 2020, the Ministry of Education allowed schools to open sequentially in four steps for different grades [15]. Schools provided hybrid instruction, consisting of online and offline classes, to limit the population density, and this method was sustained until the end of the first semester. After an additional three-week closure, school classes resumed on September 21, 2020.

Rundle et al. strongly argued that the cessation of school programs would “exacerbate the risk factors for weight gain associated with the summer recess” [16]. Previous studies have shown that the elementary school children gain more weight during the summer vacation than during the school year [17, 18]. Other studies have demonstrated that the prevalence of childhood obesity increased during the COVID-19 pandemic compared to that in the pre-COVID-19 period [19], [20], [21]. With the prolongation of the lockdown period, children were expected to gain more weight. We aimed to investigate whether there was a significant change in the weight status of children in 1 year during the COVID-19 pandemic.

Materials and Methods

Subjects

This was a retrospective study of children who visited the pediatric endocrine clinic of a tertiary hospital in Seoul. A total of 139 elementary school children aged between 6 and 12 years who underwent regular checkups for growth and puberty development were included. Children with chronic diseases that affect height and weight and those who received growth hormone therapy or gonadotropin-releasing hormone agonist therapy were excluded from the study. The study was conducted following the Declaration for Helsinki and was approved by the institutional review board (IRB) of the hospital (IRB No. 2020AN0566). Informed consent was not required, because this study used deidentified data.

Study design

We designated March 2020 as the “COVID-19 pandemic baseline” when schools were closed as a part of the nationwide lockdown due to the COVID-19 pandemic. The Ministry of Education established the school reopening plan in coordination with the social distancing stages. The numbers of children who could attend the schools were set differently for each stage. All schools followed the same distancing guidelines. School closure affected children’s activity levels. Therefore, the period was divided into three phases according to adjustment of the social distancing guidelines.

We reviewed the medical records of the subjects for data on age, sex, date of each visit, height, and weight. All children were measured for height and weight at every visit. Height was measured with a Harpenden stadiometer (Holtain Ltd., Wales, UK) with an accuracy of 0.1 cm. Weight was measured to 0.1 kg using the digital scale. Children wore the light clothing with no footwear. Measurements were performed by trained medical staffs in the endocrine clinic. Three consecutive measurements were required to increase the accuracy. The BMI and BMI z-scores were calculated using the 2017 Korean National Growth Charts for children and adolescents [22]. We investigated changes in anthropometric parameters measured repeatedly at 3 months, 6 months, and 1 year from the COVID-19 pandemic baseline. We also investigated changes in the proportion of children with overweight or obesity.

We followed the definition of normal weight and overweight used in 2017 Korean National Growth chart [22]. Children were categorized into two groups based on their BMI at the COVID-19 pandemic baseline: normal weight (fifth to <85th BMI percentile for the same age and sex) and overweight or obese (≥85th BMI percentile).

Statistical analyses

Data are shown as the mean ± standard deviation, unless otherwise mentioned. Repeated measures analysis of variance with Benjamini & Hochberg’s adjustment was used to investigate the trends for change in the BMI and BMI z-scores. Cochran’s Q test was used to analyze the variation in the proportion of children with overweight or obesity. All tests were two-tailed, and statistical significance was set at a p < 0.05. All statistical analyses were performed using IBM SPSS software (version 25.0; IBM Corp., Armonk, NY, USA).

Results

Baseline characteristics of the subjects

During 6 months from the COVID-19 pandemic baseline, we enrolled 184 children who met the inclusion criteria for our study. Forty five children who did not follow up at 1 year from the baseline were not included in the analysis.

The study included 139 children (45 [32.4%] boys and 94 [67.6%] girls) with a mean age of 9.07 ± 1.01 years. Of these, 105 (75.5%) and 45 (24.5%) were categorized into the normal-weight and overweight or obese groups, respectively. The mean BMI z-scores of boys and girls at the COVID-19 pandemic baseline were 0.16 ± 1.01 and 0.50 ± 1.05 kg/m2, respectively (p = 0.966) (Table 1).

Table 1:

Baseline characteristics of the subjects.

Characteristics (units) Total Boys Girls p-Value
Number, % 139 45 (32.4%) 94 (67.6%)
Age, yearsa 9.07 ± 1.10 9.31 ± 1.41 8.95 ± 0.91 0.130
Height, cm 138.29 ± 8.67 138.04 ± 11.1 138.41 ± 7.23 0.838
Height z-score 0.36 ± 1.12 0.04 ± 1.28 0.51 ± 1.01 0.021
Weight, kg 35.83 ± 6.87 36.01 ± 8.74 35.74 ± 5.83 0.854
Weight z-score 0.47 ± 1.22 0.06 ± 1.43 0.66 ± 1.05 0.006
BMI, kg/m2 18.58 ± 2.31 18.59 ± 2.50 18.57 ± 2.23 0.966
BMI z-score 0.39 ± 1.04 0.16 ± 1.01 0.50 ± 1.05 0.070

  1. Values are presented as numbers (%) or mean ± standard deviation.

    aAge of children at the onset of COVID-19 pandemic (March, 2020).

Changes in the BMI and BMI z-scores during the COVID-19 pandemic according to time intervals

The mean BMI of the total sample increased significantly during the study period from 18.58 ± 2.31 kg/m2 at the COVID-19 pandemic baseline to 20.33 ± 2.77 kg/m2 at 1 year from the COVID-19 pandemic baseline (p < 0.001, linear trend). BMI increased rapidly during the first 3 months from 18.57 ± 2.27 kg/m2 at the COVID-19 pandemic baseline to 19.44 ± 2.56 kg/m2 at 3 months from the baseline (p < 0.001); increased slightly during the second 3-month interval from 19.44 ± 2.56 kg/m2 at 3 months from the baseline to 19.64 ± 2.63 kg/m2 at 6 months from the baseline (p < 0.001); and increased considerably during the last 6 months from 19.64 ± 2.63 kg/m2 at 6 months from the baseline to 20.33 ± 2.77 kg/m2 at 1 year from the baseline (p < 0.001) (Table 2).

Table 2:

Changes in the BMI and BMI z-scores during the COVID-19 pandemic according to time intervals.

COVID-19 pandemic baseline 3 months from baseline 6 months from baseline 1 year from baseline
Total (n = 139)
BMI 18.58 ± 2.31 19.44 ± 2.56b 19.64 ± 2.63b,c 20.33 ± 2.77b,c,d
BMI z-score 0.39 ± 1.04 0.66 ± 1.11b 0.66 ± 1.10b 0.79 ± 1.11b,c,d

Boys (n = 45)

BMI 18.59 ± 2.50 19.55 ± 2.78b 19.75 ± 2.88b 20.56 ± 3.04b,c,d
BMI z-score 0.16 ± 1.01 0.46 ± 1.08b 0.45 ± 1.08b 0.62 ± 1.10b,d

Girls (n = 94)

BMI 18.57 ± 2.27 19.38 ± 2.45b 19.59 ± 2.52b,c 20.23 ± 2.65b,c,d
BMI z-score 0.50 ± 1.05 0.76 ± 1.11b 0.77 ± 1.10b 0.88 ± 1.12b,c,d

  1. Values are presented as the mean ± standard deviation.

    bp < 0.05 compared with the value at the COVID-19 pandemic baseline

    cp < 0.05 compared with the value at 3 months from baseline

    dp < 0.05 compared with the value at 6 months from baseline.

The mean BMI z-score also showed two significant increases: during the first 3 months, from 0.39 ± 1.04 at the COVID-19 pandemic baseline to 0.66 ± 1.11 at 3 months from the baseline, p < 0.001; and during the last 6 months, from 0.66 ± 1.10 at 6 months from the baseline to 0.79 ± 1.11 at 1 year from the baseline, p < 0.001. In contrast, the BMI z-score did not increase between 3 and 6 months from the baseline (0.66 ± 1.11 at 3 months from the baseline and 0.66 ± 1.10 at 6 months from the baseline; p = 1.000). The differences in the rate of increase in the BMI and BMI z-scores were similar between boys and girls.

Changes in the BMI and BMI z-scores according to weight status during the COVID-19 pandemic

The BMI increased rapidly during the first 3 months, from 17.60 ± 1.62 to 18.37 ± 1.81 in normal-weight group (p < 0.001); and from 21.60 ± 1.28 to 22.73 ± 1.51 in overweight and obese group (p < 0.001). The BMI z-score also increased steeply during the first 3 months, from −0.06 ± 0.67 to 0.17 ± 0.71 in normal-weight group (p < 0.001); and from 1.82 ± 0.60 to 2.18 ± 0.63 in overweight group (p < 0.001). Contrary to the increase in BMI during the first 3 months, the BMI z-score did not increase significantly during the second 3-month interval. There was a significant difference in weight change according to weight status over the next 6 months. The BMI z-score increased significantly from 0.19 ± 0.76 at 6 months from the baseline to 0.34 ± 0.82 at 1 year from the baseline in the normal-weight group (p < 0.001); however, no significant increase was noted in the overweight or obese group (2.13 ± 0.59 at 6 months from the baseline and 2.19 ± 0.63 at 1 year from the baseline; p = 1.000) (Table 3).

Table 3:

Changes in the BMI and BMI z-scores during the COVID-19 pandemic according to weight status.

COVID-19 pandemic baseline 3 months from baseline 6 months from baseline 1 year from baseline
Normal weight group (n = 105)
BMI 17.60 ± 1.62 18.37 ± 1.81b 18.58 ± 1.97b,c 19.28 ± 2.15b,c,d
BMI z-score −0.06 ± 0.67 0.17 ± 0.71b 0.19 ± 0.76b 0.34 ± 0.82b,c,d

Overweight or obese group (n = 34)

BMI 21.60 ± 1.28 22.73 ± 1.51b 22.91 ± 1.48b 23.59 ± 1.77b,c,d
BMI z-score 1.82 ± 0.60 2.18 ± 0.63b 2.13 ± 0.59b 2.19 ± 0.63b

  1. Values are presented as the mean ± standard deviation.

    bp < 0.05 compared with the value at the COVID-19 pandemic baseline

    cp < 0.05 compared with the value at 3 months from baseline

    d p < 0.05 compared with the value at 6 months from baseline.

Changes in the proportion of weight status

The proportion of children who were overweight or obese increased from 24.5% at baseline to 31.7, 34.5, and 38.1% at 3 months, 6 months, and 1 year from the baseline, respectively (χ 2 = 6.428; p for trend = 0.015) (Table 4).

Table 4:

Changes in the proportion of weight status.

COVID-19 pandemic baseline 3 months from baseline 6 months from baseline 1 year from baseline p-Value
Normal weight, % 105 (75.5%) 95 (68.3%) 91 (65.5%) 86 (61.9%) 0.001
Above overweight, % 34 (24.5%) 44 (31.7%) 48 (34.5%) 53 (38.1%)

  1. Values are presented as numbers (%).

Discussion

Our study showed that the elementary school students experienced rapid weight gain during the COVID-19 pandemic, which increased significantly over time. There was no difference according to sex, but weight gain was particularly evident in the normal-weight group during the 1-year study period.

While the lockdown strongly prevented the spread of COVID-19, the restrictions resulted in unexpected changes in lifestyle, including diet, physical activity, and sleep [10], [11], [12], [13], [14]. Instead of eating school meals, which meet age-appropriate calorie and nutrient requirements, children were exposed to delivered food and fast food, which is high in calories. Shutdown of sports facilities, reduced physical activity, and excess screen time excluding online classes also disrupted the calorie balance. Sleep patterns changed because of delays in bed time and rising time [13]. These lifestyle changes inevitably lead to weight gain during the lockdown [19, 23].

According to the growth chart, BMI generally increases with age. The BMI of Korean children aged between 6 and 12 years tends to increase by up to 0.6 kg/m2/year [22]. Our results showed an increase in BMI of approximately 1.75 kg/m2/year, which was much greater than the average yearly increase.

These changes during the school closure phase affected the trend of weight change according to social distancing restrictions. In children, weight gain was the highest during the first three months of the COVID-19 pandemic. In this early lockdown period, the level of physical activity was probably the lowest, influenced by complete school closure and strict lockdown. From May 20, 2020, the Korean government allowed partial opening of schools. Therefore, the BMI and BMI z-scores did not change significantly between 3 and 6 months from the baseline due to lockdown mitigation. With growing concerns about weight gain during lockdown, interventions for weight loss were started. The rate of increase in the BMI and BMI z-scores decreased for a while but continued to increase gradually as social isolation increased. Weight gain in children over a short period of COVID-19 lockdown has been reported by several studies [10, 19, 24, 25]. Nevertheless, our study demonstrated a sustained tendency for increase in the BMI and BMI z-scores for 1 year during the COVID-19 pandemic. Therefore, it is important to pay attention to the long-term outcomes of weight gain during the COVID-19-related lockdown in children.

During the latter 6 months, the BMI z-scores increased significantly in the normal-weight group but not in the overweight or obese group. School reopening especially helped children with overweight or obesity to control their weight. Because non-school environments are relatively under-supervised, school-based lifestyles may provide a healthier environment for children. Interventions triggered by concerns about childhood obesity might have worked more effectively in the overweight or obesity group than in the normal-weight group. A previous study revealed that children with normal weight were more likely to gain weight during school closure than children with overweight or obesity. Our study corroborated these results and found a significant shift from normal weight to overweight or obesity.

Our study had several limitations. First, the study was conducted on a small sample and only elementary school students were included. Second, variables such as diet and exercise that might influence weight changes of children had not been investigated in details. Third, we could not analyze laboratory findings related to the comorbidities of obesity. Despite these limitations, the strength of our study was that we identified the trend of increase in BMI under changing social distancing conditions and examined relatively long-term data spanning 1 year to follow the trend of weight change.

In conclusion, our study revealed that the BMI and BMI z-scores of elementary school-aged children gradually increased during the lockdown due to the COVID-19 pandemic. As there is uncertainty regarding the duration of lockdown, we need to support families with children in maintaining healthy habits at home during the lockdown period and develop social programs to prevent childhood obesity from a long-term perspective.


Corresponding author: Kee-Hyoung Lee, Department of Pediatrics, College of Medicine Korea University, Seoul, South Korea, E-mail:

Acknowledgments

All authors are grateful to the participants of this study.

  1. Research funding: None declared.

  2. Author contribution: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

  3. Competing interests: Authors have no conflicts of interest to declare.

  4. Ethical approval: The local Institutional Review Board deemed the study exempt from review.

  5. Employment or leadership: None declared.

  6. Honorarium: None declared.

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Received: 2021-08-23
Accepted: 2021-11-18
Published Online: 2021-12-08
Published in Print: 2022-03-28

© 2021 Walter de Gruyter GmbH, Berlin/Boston