Underweight among Danish schoolchildren is overlooked

Diet and lifestyle 14. dec 2023 2 min Research group leader, PhD Jennifer Lyn Baker Written by Kristian Sjøgren

In recent years, doctors and researchers have strongly focused on children developing obesity. However, a new study shows that many children have underweight. The researchers involved in the study say that children with underweight must not be neglected, since being underweight can have very adverse and lifelong effects on health.

More and more children in high-income countries have overweight, many with obesity.

The increase in the number of children with overweight has led to a natural focus on them, since overweight and especially obesity can have lifelong adverse health, mental health and social effects.

Despite all the focus on children with overweight, the many children with underweight are also important. A new study from Denmark found that more children have underweight than obesity.

Having overweight can lead to health problems but so can having underweight. According to a researcher behind the study, children should be in focus and their weight should be monitored based on regular school-based health examinations.

“This study is very interesting because the great focus on children with overweight or obesity in recent years may have overshadowed the problems of children with underweight. Neither society nor the healthcare system should forget that we must monitor weight trends not only among children with overweight but also among all other children,” explains Jennifer Lyn Baker, Research Group Leader, Section for Epidemiology, Bispebjerg and Frederiksberg Hospital, Copenhagen.

The research has been published in Acta Paediatrica.

Data from nearly 400,000 schoolchildren

The researchers used the Copenhagen School Health Records Register to map the trends in schoolchildren’s weight from the 1930s to the 2000s. It contains information from the regular school-based health examinations in the City of Copenhagen in which doctors or nurses weighed schoolchildren born between 1930 and 1996.

The children were measured and weighed several times from age 6 to 14 years.

The data enabled the researchers to calculate the body mass index (BMI) for all the children and determine how BMI changed over time.

The study included data on 197,964 girls and 201,276 boys. The researchers calculated the BMI of about 2.4 million children classified as having underweight, normal weight, overweight or obesity at different ages during childhood.

“We found that the proportion of children with overweight has generally increased over the years, whereas the proportion of children with underweight has declined, especially in recent decades,” says another researcher involved in the study, Julie Aarestrup, Researcher, Center for Clinical Research and Prevention, Bispebjerg and Frederiksberg Hospital, Copenhagen.

Vast change in the proportions of children with underweight and overweight

The results for girls aged 7 years showed that 10% had underweight, 4% had overweight and 0.3% had obesity from 1937 to 1946, when the first measurements were made. In the most recent measurements from 1997 to 2004, the percentage having underweight had declined to 7%, whereas 15% had overweight and 5% obesity.

These data also mean that the proportion of children with normal weight declined. Among children aged 7 years, 86% of girls and 89% of boys had normal weight from 1937 to 1946 versus 73% and 79%, respectively, from 1997 to 2004.

The study also shows that more children had underweight than overweight until the 1980s.

More children still had underweight than obesity in 1997–2004, with 15% of girls and 11% of boys aged 7 years having overweight and 5% of the girls and 4% of the boys having obesity.

The proportion of children aged 7 years with underweight was 7% for girls and 6% for boys in 1997–2004.

“This reminds us that we need to monitor the weight of all children and not just focus on those with obesity,” explains Jennifer Lyn Baker.

Vital to continue monitoring children’s weight

According to Jennifer Lyn Baker, the study provides important information.

The weight of all children should be monitored, since both overweight and underweight can have lifelong health effects.

Having overweight can lead to cardiovascular disease, diabetes and other somatic diseases and various mental health conditions.

Having underweight increases the risk of menstrual irregularity among girls and increases susceptibility to infections. Having underweight is also associated with an increased risk of developing osteoporosis later in life.

Awareness is key

According to Jennifer Lyn Baker, the study contributes to understanding the importance of a system to routinely monitor children’s weight and height without stigmatising them.

“Monitoring children’s weight and health enables us to determine whether the situation is worsening over time. School-based monitoring is extremely relevant and important and should be given priority since it can identify children before serious health problems develop,” says Jennifer Lyn Baker.

Julie Aarestrup points out that many children are still underweight today, which shows the need for focusing attention on both ends of the BMI spectrum.

“Monitoring the trends in children’s BMI over time makes us more aware of what has historically influenced the prevalence of both overweight and underweight among school-aged children. We can use this knowledge to promote health among all children,” she concludes.

Jennifer L. Baker is the leader of the Lifecourse Epidemiology group in the Section of Clinical Epidemiology at the Center. Jennifer received her PhD...

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