While living in cities can offer many benefits, such as access to cultural events, diverse populations, and educational opportunities, there are also several health-related challenges that children and teens face in urban environments.
According to a new global analysis of trends in child and adolescent height and body mass index (BMI) led by Imperial College London and published in Nature, the benefits of living in cities for healthy growth and development of children and adolescents are diminishing across much of the world. From 1990 to 2020, a global consortium of over 1500 researchers and physicians examined height and weight data from 71 million children and adolescents (aged 5 to 19 years) in urban and rural areas of 200 countries.
Cities can provide a multitude of opportunities for better education, nutrition, sports and recreation, and healthcare which contributed to school-aged children and adolescents living in cities being taller than their rural counterparts in the 20th century in all but a few wealthy countries.
Our findings should inspire policies that combat poverty and make nutritious foods more affordable in order to ensure that children and adolescents grow and develop into adults who lead healthy and productive lives.
Professor Ezzati
According to the new study, this urban height advantage has shrunk in most countries in the twenty-first century as a result of accelerating improvements in height for children and adolescents in rural areas.
The study also looked at children’s BMI, which is an indicator of whether or not they are a healthy weight for their height. In 1990, children in cities had a slightly higher BMI than children in rural areas, according to the researchers. Most countries’ BMI averages rose by 2020, albeit faster for urban children, with the exception of Sub-Saharan Africa and South Asia, where BMI rose faster in rural areas.
Nevertheless, over the 30-year period, the gap between urban and rural BMI remained small — less than 1.1kg/m² globally (less than 2kg in weight for a child who is 130cm tall or less than 3kg in weight for an adolescent who is 160cm tall).
“Cities continue to provide significant health benefits for children and adolescents,” said Dr Anu Mishra of Imperial College London’s School of Public Health. Fortunately, thanks to modern sanitation and improvements in nutrition and healthcare, rural areas are catching up to cities in most regions. The findings of this large global study call into question commonly held beliefs about the negative aspects of city living in terms of nutrition and health.”
While global height and BMI have increased since 1990, the researchers discovered that the degree of change between urban and rural areas varied greatly across middle and low-income countries, while small urban-rural differences remained stable across high-income countries.
Middle-income and emerging economies, such as Chile, Taiwan, and Brazil, have seen the greatest gains in rural children’s height over the last three decades, with children living in rural areas reaching similar heights as their urban counterparts.
“These countries have made great strides in leveling up,” said senior author Majid Ezzati of Imperial College London’s School of Public Health. Using economic growth resources to fund nutrition and health programs, both in schools and in the community, was critical to closing the gap between different areas and social groups.”
In addition, contrary to the widely held belief that urbanization is the primary cause of the obesity epidemic, the study discovered that many high-income Western countries have had very little difference in height and BMI over time, with the difference between urban and rural BMI differing by less than one unit in 2020 (roughly 1.5kg of weight for a child of 130cm).
“The issue is not so much whether children live in cities or urban areas, but where the poor live, and whether governments are addressing growing inequalities with initiatives like supplementary incomes and free school meal programs,” Professor Ezzati added.
The trend in sub-Saharan Africa is also a cause for concern, researchers say. Boys living in rural areas have plateaued in height or even become shorter over the three decades, in part because of the nutritional and health crises that followed the policy of structural adjustment in the 1980s.
Professor Andre Pascal Kengne, co-author for the study, from the South African Medical Research Council, said: “Rural sub-Saharan Africa is now the global epicentre of poor growth and development for children and adolescents. As the cost of food skyrockets and countries finances get worse due to the COVID-19 pandemic and the war in Ukraine, the rural poor in Africa are at risk of falling further behind.”
In 2020, Rwanda (around 4cm) and the Democratic Republic of the Congo, Ethiopia, and Mozambique all had 2-3.5cm height gaps between urban and rural boys. Boys and girls in Sub-Saharan Africa gained weight faster in rural areas than in cities over time, which meant that in some countries, they progressed from being underweight to gaining too much weight for healthy growth.
“This is a serious problem at every level, from individual to regional,” Professor Ezzati said. Slowing growth in school-aged children and adolescents is strongly linked to poor health throughout life, missed educational opportunities, and the enormous cost of unrealized human potential.”
“Our findings should inspire policies that combat poverty and make nutritious foods more affordable in order to ensure that children and adolescents grow and develop into adults who lead healthy and productive lives. Healthy food vouchers for low-income families and free school meals can also provide long-term benefits to children’s and adolescents’ health and well-being.”
