‘Concerning’ BMI, height trends observed among school-aged children worldwide
A new analysis shows highly variable trajectories over time in the height and BMI of school-aged children across countries, raising concerns about access to healthy foods and global nutrition programs.
The findings, published in The Lancet, are the first comparable estimates of height in school-aged children and adolescents for all countries in the world alongside estimates of BMI, analyzed with age trajectories of mean height and BMI to investigate ages when growth in different countries was more vs. less healthy.
“Children’s height and weight are indicators of the quality of their diet and living environment and predictive of future health and wellbeing of each generation,” Majid Ezzati, PhD, MA, professor of global environmental health at Imperial College London and at the MRC-PHE Centre for Environment and Health, told Healio. “We wanted to understand their variation, and how they have changed, for all the countries in the world.”
Weight, height trends
In a pooled analysis, Ezzati and colleagues analyzed a database of cardiometabolic risk factors collated by the Non-Communicable Disease Risk Factor Collaboration. Researchers used a Bayesian hierarchical model to estimate trends from 1985 to 2019 in mean height and mean BMI in 1-year age groups for ages 5 to 19 years.
“The model allowed for nonlinear changes over time in mean height and mean BMI and for nonlinear changes with age of children and adolescents, including periods of rapid growth during adolescence,” the researchers wrote.
Researchers then pooled data from 2,181 population-based studies with measurements of height and weight for 65 million participants in 200 countries and territories.
In 2019, the estimated difference was 20 cm or higher in mean height of adolescents aged 19 years between countries with the tallest populations and the shortest populations for boys and girls, stratified by sex. In the same year, the differences between countries with the highest mean BMI and lowest mean BMI for boys and girls, stratified by sex, was approximately 9 kg/m² to 10 kg/m².
“In some countries, children aged 5 years started with healthier height or BMI than the global median, and in some cases, as healthy as the best performing countries, but they became progressively less healthy compared with their comparators as they grew older by not growing as tall,” the researchers wrote.
In 2019, adolescents aged 19 years who were on average the tallest in the world lived in the Netherlands (mean height, 183.8 cm), followed by Montenegro, Estonia, and Bosnia and Herzegovina for boys; the tallest girls lived in the Netherlands (mean height, 170.4 cm), followed by Montenegro, Denmark and Iceland. Adolescents who were on average the shortest in 2019 lived in Timor-Leste (mean height, 160.1 cm), followed by Laos, Solomon Islands and Papua New Guinea for boys, and Guatemala (mean height, 150.9 cm), followed by Bangladesh, Nepal and Timor-Leste for girls.
“The 20 cm or higher difference between countries with the tallest and shortest mean height represents approximately 8 years of growth gap for girls and approximately 6 years for boys,” the researchers wrote.
Researchers found that Pacific island countries in Oceania had the highest mean BMI in the world in 2019, surpassing 28 kg/m² for adolescents. Late-adolescence BMI was also high for boys and girls in Middle Eastern and north African countries, such as Kuwait and Bahrain, in Caribbean islands, such as the Bahamas, in Chile, the United States and New Zealand and for girls, in South Africa.
The mean BMI of boys and girls aged 19 years was lowest (approximately 21 kg/m² or lower) in India, Bangladesh, Timor-Leste, Ethiopia and Chad, and was lowest for girls aged 19 years in Japan and some central European countries, such as Romania and Bosnia and Herzegovina.
“The highest and lowest worldwide BMIs were approximately 9–10 kg/m² apart, equivalent to about 25 kg of weight,” the researchers wrote.
Researchers also found that children in many countries grew healthily to age 5 years, with height and weight in the healthy range as defined by WHO; however, children in some countries fell behind during school years, gaining too much weight or too little height for healthy growth.
Researchers wrote that the unhealthiest changes — gaining too little height, too much weight for their height compared with children in other countries, or both — occurred in many countries in sub-Saharan Africa, New Zealand and the U.S. for boys and girls; in Malaysia and some Pacific island nations for boys; and in Mexico for girls.
“There is enormous variation across countries in these important measures of nutrition, development and health, and school-aged children in many countries do not fulfill their potential for healthy growth, even among some that do so in younger ages,” Ezzati told Healio. “Poor nutrition in childhood adolescence, not gaining enough height and too little or too much weight, can lead to a range of diseases later in life.”
The researchers noted that findings may be affected by a lack of data in some countries, particularly in the Caribbean, Polynesia and Micronesia, Melanesia and sub-Saharan Africa. Additionally, less than half of the studies had data for children aged 5 to 9 years compared with almost 90% for children aged 10 to 19 years, meaning there is more uncertainty in those estimates, they wrote.
Creating ‘Goldilocks’ countries
In commentary accompanying the study, Susan M. Sawyer, MD, director of the Centre for Adolescent Health at the Royal Children’s Hospital, Melbourne, Australia, wrote that the findings reinforce the importance of promoting healthy growth across the developmental years.
“The results presented in this paper suggest that we need to work harder to create ‘Goldilocks’ countries — countries where, over time, children have sufficiently balanced social, physical and nutritional environments, that average heights have increased over time but without unhealthy increases in BMI,” Sawyer told Healio. “Sadly, in this study, too many countries had children with less healthy growth trends over time, such that while average heights were increasing, they also experienced ‘too much’ in terms of BMI increases. Of particular concern was the poorest countries where not enough growth early on was then compounded by unhealthy BMI increases in later childhood and adolescence, with known future risks for non-communicable diseases.”
Sawyer said the clinical implications are that “beyond the early years of life, growth must continue to be measured across the full span of childhood and adolescence, as earlier growth patterns in both height and weight can change. ”