An international research group pooled data for height and weight for 65 million children and adolescents in 200 countries and territories. The analysis provides unique insight into how the developmental and health outcomes of school-aged children and adolescents vary across countries worldwide.
An international research group with Danish participation carried out the most comprehensive survey of how school-aged children and adolescents 5–19 years old develop.
The researchers pooled data from 2,181 population-based studies from around the world that measured the height and weight of 65 million children and adolescents in 200 countries and territories from 1985 to 2019.
Based on the data, researchers can now obtain much better insight into the variation that exists between children worldwide, the trends over the past 35 years and how children develop until adulthood starts. This has implications for their health and developmental outcomes throughout life.
“This is an incredibly comprehensive analysis of what happens to school-aged children and adolescents up to the age of 19 years. Much global health and nutrition research has focused on children from preconception to age 5 years because the World Health Organization (WHO) has been very interested in them. However, we have lacked data from a very important period in the long-term development of children and adolescents because what happens during this period in their lives can greatly influence the development of various chronic diseases such as type 2 diabetes,” explains co-author Thorkild I.A. Sørensen, Professor Emeritus, Novo Nordisk Foundation Center for Basic Metabolic Research, and Section of Epidemiology, Department of Public Health, University of Copenhagen.
The research has been published in The Lancet.
Insight into global health status
A group of researchers from Imperial College London led the study and pooled data from around the world.
One data source was school records, which enabled the researchers to determine the height and weight of school-aged children and adolescents in various countries.
Based on the data, they analysed the trends in children’s in height and body mass index (BMI) through adolescence and over time – for example, whether children and adolescents in Denmark are taller today than they were in the mid-1990s.
The information on trends in children’s height and weight clearly indicates the general health trends among children and adolescents in a given country. Not growing over time or having very high BMI are signs that something is wrong with their health that needs to be addressed politically.
“The study is just one in a series of global studies on the differences in the risk of noncommunicable diseases, such as cardiovascular disease, across the globe. This requires understanding the risk in each country, how it has changed and what the risk is relative to other countries,” says Thorkild I.A. Sørensen.
Girls in Denmark among the tallest in the world
One result shows that the mean height of 19-year-old boys in the Netherlands, Montenegro, Estonia and Bosnia and Herzegovina differs by about 20 cm or more from that of boys from Timor-Leste, Laos, Solomon Islands and Papua New Guinea.
Similarly, mean height among girls from the Netherlands, Montenegro, Denmark and Iceland differs from that among girls from Guatemala, Bangladesh, Nepal and Timor-Leste.
Specifically, the mean height among 19-year-olds in the Netherlands born in 2000 was 183.8 cm for boys and 170.4 cm for girls. Similarly, the mean height of 19-year-old boys in Timor-Leste born in 2000 is 160.1 cm, and the mean height of a 19-year-old girl in Guatemala born in 2000 is 150.9 cm.
Another way of looking at this is that a 12-year-old girl in the Netherlands born in 2000 has the same mean height as a 19-year-old girl from 53 countries, including Burundi, India, Indonesia, Laos, Pakistan, Peru and Yemen.
Children in Denmark among the countries with the healthiest trends
For both boys and girls, the 19-year-old adolescents with the highest mean BMI are in Pacific island countries, Kuwait, Bahrain, the Bahamas, Chile, the United States and New Zealand.
In Pacific island countries in Oceania, such as Samoa and Fiji, the mean BMI of 19-year-old boys born in 2000 is 28 kg/m2. People with BMI exceeding 25 are considered to be overweight.
For girls, the same countries have the highest mean BMI.
Countries such as India, Bangladesh and countries in eastern and central Africa have the lowest mean BMI: the mean BMI of 19-year-old boys and girls is about 21 kg/m2.
The researchers also found great differences in how much mean BMI changed from 1985 to 2019.
In Denmark and Russia, for example, BMI registered small changes of less than 0.5 kg/m2 from 1985 to 2019.
In contrast, from 1985 to 2019, late-adolescence BMI increased more than 3 kg/m2 for both sexes in Malaysia and some countries in Oceania, for girls in Mexico and for boys in China.
“Comparing countries is interesting. There are substantial variations across countries and in their trends over time. In some countries, school-aged children and adolescents are taller, and in other countries they have a higher BMI. In some countries, BMI and height are correlated, but BMI has reduced in some countries. Now we can start to discuss the causes of these differences,” explains Thorkild I.A. Sørensen.
Thorkild I.A. Sørensen also says that Denmark’s trends are among the healthiest in the world: a small increase in BMI and a large gain in height.
The mean is not the most important in health data
Although the new study provides new insight into the growth and development of school-aged children and adolescents since 1985, according to Thorkild I.A. Sørensen, the information does not say anything about how healthy children and adolescents are today.
The figures are mean values that provide a snapshot of how school-aged children and adolescents are doing on average but does not say anything about the whole data set.
Did the mean values change because many school-aged children and adolescents became much taller or because all children and adolescents became slightly taller?
The same question is relevant for weight.
“The most interesting part is the extreme values in the tails of the distribution curves for height and weight. For example, why do some children get very fat, and what can we do about it? Why do some children not grow the way other children do? The mean is enormously valuable, but we also need to examine the individual data to determine what underlies the numbers. If we know the basis for the figures, we can take the first step towards potentially preventing an undesirable trend,” says Thorkild I.A. Sørensen.
However, Thorkild I.A. Sørensen is sure that WHO will think that the results are very interesting, because it provides an evidence base on trends in health status in countries and territories in the school-aged group on which there has been less focus.