Impact of COVID-19 lockdown on BMI of obese and normal-weight children in Switzerland

In a recent study posted to the Research Square* pre-print server and under consideration at the BMC Pediatrics journal, a team of researchers evaluated the effects of the coronavirus disease 2019 (COVID-19)-related lockdown in spring 2020 in Switzerland on the body mass index (BMI) of children treated for obesity, in comparison to earlier times and with that of normal-weight children.

Study: Evaluation of the Impact of the COVID-19 Lockdown on BMI in Children and Adolescents with or Without Obesity. Image Credit: Paranyu/ShutterstockStudy: Evaluation of the Impact of the COVID-19 Lockdown on BMI in Children and Adolescents with or Without Obesity. Image Credit: Paranyu/Shutterstock

The prevalence of obesity in children has become a great healthcare challenge worldwide, particularly in Europe, with prevalence levels of 20-25%. The lockdown in Switzerland negatively impacted the BMI of children and adults under treatment for obesity; this subset of the population, compared to normal-weight children and adults, was severely affected by the nationwide cessation of activities, including the closing of schools and sports clubs. Although studies have reported changes in lifestyle behaviors in obese children and adults during the lockdown, none monitored their weight; and studies reporting weight gain relied on self-reported weight measurements and not standardized measures.

About the study

In the present retrospective study, researchers collected demographic and anthropometric data of children in the age group of 2–18 years with obesity (subjects with obesity) and the normal-weight children (control subjects) to monitor changes in their BMI and weight gain during their visit to obesity clinics in Geneva at four-time points: before and post the lockdown period, from March 15 to May 11, 2020, and at the same times during 2019.

There were 47 children in the obese group and 20 in the control group. As the number of children in each group impacted the effect size of the study, the authors observed that the effect size was 0.997 (large) in 2020. It was enough to detect a difference of BMI change of 0.45 ± 0.35 between obese and control subjects.

The researchers noted children’s age and gender, as well as body weight (kg) in light clothes and height (cm) without shoes. They calculated body mass index (BMI) as weight/height squared (kg⋅m-2). Although they used BMI z-score, they used BMI changes when comparing normal-weight and weight of obese subjects as BMI z-score is inaccurate to track changes in severely obese children. BMI z-scores were derived using the World Health Organization references, with BMI z-score of <-1 standard deviation (SD), -1 to + 1SD, >+ 1SD, >+ 2SD, and > + 3SD indicated underweight, normal weight, overweight, obese, and severe obesity, respectively.

For statistical analyses, the researchers used paired t-tests to assess changes in weight, BMI, and BMI z-score. For drawing evolutionary comparisons of anthropometric data of the two study groups, they used linear and standard multiple regressions; additionally, Chi-square tests or independent student’s t-tests. However, when they used the Pearson correlation coefficient to compare groups, differences were considered as significant only for p < 0.05.


On average, a BMI increase of 0.3 points every 3 months indicates normal growth involving both weight gain and height increase. Although the authors noted that weight and BMI increased for both control subjects and subjects with obesity during the two studied periods, the increase in magnitude was not the same between the two groups.

During almost a similar time interval, in 2019 and 2020, subjects with obesity gained twice as much weight as control subjects. There could be two likely explanations for this. First, obese children tend to gain weight. The second could be that since subjects with obesity were one year older, some of them were further along in the puberty process, and grew significantly more (height +2 cm vs. +1 cm in the control subjects), even after age adjustment. However, this is just an assumption, as the authors did not make puberty assessments during this study. 

Nevertheless, weight gain was more pronounced in the subjects with obesity. For them, the difference in the magnitude during the 2020 lockdown period and between 2019 and 2020 was 1.3 kilo compared to a difference of only 0.5 kilos in the control group. Interestingly, an almost identical magnitude of weight gain was observed in adult studies.

Similarly, while the BMI increased in both groups in 2019, this increase was more pronounced during the lockdown in 2020 for subjects with obesity. The changes in BMI between 2019 and 2020 were 0.6 points in subjects with obesity, compared to only 0.05 points in the control group. Unfortunately, it was difficult for children and families dealing with obesity issues to seek help when the environment and living conditions changed drastically due to the COVID-19-related lockdown when no medical support was available.

Another interesting result related to the weight range or BMI changes was that subjects with obesity tended to display more extreme changes than controls, especially in 2020. Control subjects did not show such extreme changes, struggled less with food choices or quantities, and were still physically active even when their usual physical activities were hindered.

As the subjects with obesity also increased their height more than the controls even after adjustment for age, the BMI evolution was similar between the two groups in 2019 and 2020, but the difference almost reached statistical significance in 2020. Furthermore, the difference in BMI evolution between 2019 and 2020 was not significant when comparing the two groups, even if subjects with obesity seemed to have increased their BMI more in 2020 than in 2019.


The study highlighted the challenges and complexities associated with obesity management. Considering these polarized changes in both weight gain and weight loss in the population of obese adults and children in Switzerland, the authors recommended active support for families with an overweight child or adolescent.

*Important notice

Preprints with Research Square publish preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Neha Mathur

Written by

Neha Mathur

Neha is a digital marketing professional based in Gurugram, India. She has a Master’s degree from the University of Rajasthan with a specialization in Biotechnology in 2008. She has experience in pre-clinical research as part of her research project in The Department of Toxicology at the prestigious Central Drug Research Institute (CDRI), Lucknow, India. She also holds a certification in C++ programming.


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