Diminishing health benefits of living in cities for children and teens

The advantages of living in cities for children and adolescents’ healthy growth and development are shrinking across much of the world, 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 research, by a global consortium of more than 1500 researchers and physicians, analysed height and weight data from 71 million children and adolescents (aged 5 to 19 years) across urban and rural areas of 200 countries from 1990 to 2020.

Cities can provide a multitude of opportunities for better education, nutrition, sports and recreation, and healthcare that contributed to school-aged children and adolescents living in cities being taller than their rural counterparts in the 20^th century in all but a few wealthy countries.

The new study found that in the 21^st century, this urban height advantage shrank in most countries as a result of accelerating improvements in height for children and adolescents in rural areas.

The study also assessed children’s BMI—an indicator of whether they have a healthy weight for their height. The researchers found that on average children living in cities had a slightly higher BMI than children in rural areas in 1990. By 2020, BMI averages rose for most countries, albeit faster for urban children, except in 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).

Dr Anu Mishra, lead author of the study, from Imperial College London’s School of Public Health, said: “Cities continue to provide considerable health benefits for children and adolescents. Fortunately, in most regions, rural areas are catching up to cities thanks to modern sanitation and improvements in nutrition and healthcare.

“The results of this large global study challenge the commonly held perceptions about the negative aspects of living in cities around nutrition and health.”

While height and BMI has increased around the world since 1990, the researchers found that the degree of change between urban and rural areas varied greatly among different 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 biggest gains in rural children’s height over the three decades, with children living in rural areas growing to similar heights as their urban counterparts.

Professor Majid Ezzati, senior author for the study, from Imperial College London’s School of Public Health, said: “These countries have made great strides in levelling up. Using the resources of economic growth to fund nutrition and health programmes, both through schools and in the community, was key to closing the gaps between different areas and social groups.”

And contrary to the widespread assumption that urbanisation is the main driver of the obesity epidemic, the study found that many high-income western countries have had very little difference in height and BMI over time—with the gap between urban and rural BMI differing by less than one unit in 2020 (close to 1.5kg of weight for a child of 130cm).

Professor Ezzati added: “The issue is not so much whether children live in cities or urban areas, but where the poor live, and whether governments are tackling growing inequalities with initiatives like supplementary incomes and free school meal programmes.”

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.”

Particularly large height gaps between urban and rural boys in 2020 were seen in Rwanda (around 4cm) and in the Democratic Republic of Congo, Ethiopia, and Mozambique—all by 2-3.5cm.

Over time, boys and girls in sub-Saharan Africa also gained weight more rapidly in rural areas than cities, which meant that in some countries they went from being underweight to gaining too much weight for healthy growth.

Professor Ezzati said: “This is a serious problem at every level, from individual to regional. Faltering growth in school-aged children and adolescents is strongly linked to poor health through life, lost educational attainment and the immense cost of unrealised human potential.”

“Our findings should motivate policies that counter poverty and make nutritious foods affordable to make sure that children and adolescents grow and develop into adults who have healthy and productive lives.

“Programmes like healthy food vouchers for low-income families and free school meal programmes can also provide lifelong benefits for children and adolescent’s health and wellbeing.”

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‘Diminishing benefits of urban living for children and adolescents’ health’ by Anu Mishra et al. is published in the journal Nature.

The full paper will be available via this link when the embargo lifts: https://www.nature.com/articles/s41586-023-05772-8

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Conrad Duncan (he/him)

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Imperial College London

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Email: c.duncan@imperial.ac.uk

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NOTES TO EDITOR:

The study was funded by UKRI (MRC), Wellcome Trust, the European Union and a charitable grant from the AstraZeneca Young Health Programme.

Height and body mass index (BMI) reflect the quality of nutrition and healthiness of the environment during childhood and adolescence and are important indicators of health and developmental outcomes throughout life.

Having low height and/or excessively low BMI increases the risk of illness and premature death, and low height is associated with impaired cognitive development and reduced educational performance and work productivity later in life. Similarly, high BMI in childhood and adolescence is linked with a greater risk, and earlier onset of, chronic diseases like type 2 diabetes and high blood pressure, as well as poor mental health and educational outcomes.

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Regional and country data on height and BMI in rural and urban populations

• The height gap has narrowed substantially between urban and rural children in countries in central and eastern Europe (Croatia), Latin America (Argentina, Brazil, Chile and Paraguay), east and southeast Asia (Taiwan), and for girls in central Asia (Kazakhstan and Uzbekistan), where rural children were able to attain heights similar to their urban counterparts. 
• In China, Romania, and Vietnam, the height gap between urban and rural areas shrank but young people living in cities remained taller than their rural peers in 2020—by 1.7-2.5cm.
• In contrast, among boys, the urban height advantage slightly increased in east African countries like Ethiopia, Rwanda, and Uganda, all by around 1cm. This gap remained largely unchanged for girls in sub-Saharan Africa and south Asia. 
• By 2020, boys and girls living in cities in Andean and central Latin American countries like Bolivia, Panama and Peru were taller than their rural counterparts by some of the largest margins—by up to 4.7cm taller for boys and 3.8 cm for girls.
• Urban boys in sub-Saharan African countries like the Congo, Ethiopia, Mozambique and Rwanda were persistently taller than their rural counterparts by a large margin—up to 4.2cm in 2020. 
• BMI of children and adolescents increased in urban and rural areas of all countries worldwide with only a few mostly high-income exceptions where there were slight (<1kg/m2) declines (boys in Spain and Italy, and girls in Denmark).
• Globally, the BMI gap between cities and rural areas has changed very little since 1990. Nevertheless, urban children’s BMI increased slightly more than rural children in middle-income countries in east and southeast Asia, Latin America and the Caribbean, and Middle East and north Africa. The largest increase was in boy and girls in Vietnam (by 0.5kg/m2 for boys and 0.7 kg/m2 for girls).
• In the majority of countries in sub-Saharan Africa and south Asia, BMI of children and adolescents increased more in rural areas than in cities, leading to a closing of the urban–rural difference alongside a shift in average BMI of boys and girls in rural regions out of the range for being underweight, and increasingly towards unhealthy weight for their height.

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