A new global study, which analyzed data from over 70 million children and adolescents in 200 countries and territories, has shown that growing up in cities no longer guarantees height and weight advantages, as it did in the past.
The study, published in Nature, found that urban areas still had slightly taller and heavier children than rural areas in most countries in 1990. However, the urban advantage has declined in the past three decades, especially in high-income countries, where some boys are now shorter than their rural peers.
The study used data from 2,325 population-based studies conducted between 1990 and 2020, which measured the height and weight of 5- to 19-year-olds. The researchers found that the urban height advantage became smaller and, in some cases, reversed, with urban boys being shorter than rural boys in most countries.
This was particularly true in sub-Saharan Africa, where rural boys did not gain height or even became shorter, further widening the gap with their urban peers. The trend was less pronounced for girls, whose height and weight were generally more similar across urban and rural areas.
While the difference in body-mass index (BMI) between urban and rural children and adolescents was small, less than 1.1 kg/m² in most countries, it increased slightly more in cities than in rural areas in general, except in some parts of Asia, Africa, and Europe. The study did not explore the reasons behind the changes in growth patterns, but factors such as nutrition, physical activity, pollution, and social and economic inequality could be responsible.
The study’s lead author, Majid Ezzati from Imperial College London, said that the findings challenge the widely held assumption that urbanization is universally associated with better health. As the world continues to urbanize, with about two-thirds of the population projected to live in cities by 2050, it is critical to understand how urban environments affect children’s health and well-being and how we can design cities to optimize their growth and development.
The report highlights the importance of optimal growth and development during childhood and adolescence for lifelong health and well-being. Low height and BMI increase the risk of morbidity and mortality and can impair cognitive development, and reduce educational and work productivity.
Although efforts were made to gather data from all countries, some had limited data, particularly in the Caribbean, Polynesia, Micronesia, and sub-Saharan Africa. The available studies had fewer data on children aged 5-9 years compared to 10-19-year-olds. This lack of data increases the uncertainty of the estimates for these countries and regions, particularly for younger age groups.
The report suggests including school-aged children in health and nutrition surveys systematically, using schools as a platform for monitoring growth and developmental outcomes, in order to address this. Additionally, when analyzing the growth and development of children within rural or urban areas, there is a need to consider the socioeconomic status and community characteristics.