Science has long assumed that urban children grow faster and healthier than rural children, but that trend has reversed over the past three decades, a new study shows. The global study, published on Wednesday at Nature found that the average height urban children and teenagers aged 5 to 19 are now slightly shorter than their peers in rural areas in most countries, especially in wealthy countries such as the US, UK and France.
“While historically we have seen fairly clear benefits from living in cities, those benefits have diminished slightly over time,” says study co-author Honor Bixby, research fellow in population health and epidemiology at the University of Essex in England. “But it can be seen as a positive in that the rural height is really catching up.”
However, researchers are still trying to figure out exactly why this is happening.
Cities have long been associated with better health – researchers call it “urban advantage“. Residents in bustling, developed centers are likely to have better access to quality health care, education, safety, and nutrition, and barriers to these resources can particularly impact critical early childhood growth. “This early stage of life really sets the tone for health in adulthood and later in life,” says Bixby, who worked on the study with more than 1,500 researchers in the Collaboration on Noncommunicable Disease Risk Factors, a worldwide network of scientists and physicians. “We specifically consider height and body mass index (BMI) as anthropometric measures of growth and development because [height and weight are] both nutritional quality and environmental health.” (Some experts and members of the public criticized BMI limitsits overuse as an accurate measure of health and its failure to capture variability between individuals. Bixby says it can still be useful for estimating population-level means and trends.)
The study analyzed data from 71 million participants from 2,325 population-based studies conducted between 1990 and 2020 in 200 countries and territories. In 1990, children living in cities were higher than children in rural areas, although the difference was not significant in most high-income countries. However, by 2020, while overall child height has increased in both urban and rural areas, in most countries children in urban areas have shown smaller growth gains.
“What happened was a brilliant result, especially since the difference in BMI was actually much smaller than the height,” says Bixby. “When we talk about a small urban disadvantage, we mean that the average height of a population living in cities is slightly less than the average height of a person living in a rural area in the same country.”
This change may mean that the gap in health care resources between the two populations is narrowing. But is this due to the deteriorating health of city dwellers, or to the improvement in the health of rural dwellers? It is also difficult to determine whether the changes were driven by socioeconomic factors or population displacement, or a combination of the two, says Mahesh Karraassistant professor of global development policy at Boston University who was not involved in the new study.
Natural migration and urban expansion are factors that can influence who lives in cities today. According to a 2018 United Nations report, 55 percent of the world’s population then lived in cities. “For the first time in human history, the majority of people live in urban areas, but now this is changing the relative composition of those who live in rural versus urban areas,” Carra says. “The composition is also changing because there is a lot of migration from the countryside to the cities. People are much more mobile these days and this is becoming [difficult to] unravel these average effects.”
Bixby says migration may be at the heart of some of the changes, but is likely not a major driver of recent trends. Past migration studies have shown that, over time, newcomers end up acquiring the same health characteristics of the population they move to, she said, because they gain access to the same services. For example, children who move to the city will go to the same schools and use the same services as those who have already lived there. “There is much more to be said about where migrants fit in the socioeconomic distribution and whether they can take full advantage of cities, but this is more about socioeconomic inequality than migration per se,” says Bixby. “It is true that we simply do not have the data to properly assess the role of migration in our study.”
Karra agrees that migration is probably not the main cause of elevation change in cities. “The cynical point of view is that if you imagine sicker people moving from rural areas to urban areas, because they know that urban areas [provide] the best care,” he explains. Theoretically, this could reduce the level of health in cities and reduce the gap between the population. “But that is if urban areas are falling in terms of their development,” Carra adds. “Basically, you see both urban and rural health improving; BMI and height increase over time. But in rural areas it grows faster than in urban areas, and this is where you start to see either better health or better selection of people who continue to stay in the countryside.”
Bixby adds that countries where improvements in rural elevation have been most evident may be seeing economic growth or investment in higher living standards. While the overall increase in height in both rural and urban areas is a positive trend, it highlights that inequalities continue to persist, especially in Sub-Saharan Africa, South Asia, the Pacific, and the Middle East. Boys living in rural areas in these regions did not grow taller, and in some countries in these regions the average height of boys became shorter regardless of where they lived.
“It’s not that we’ve closed the gaps, it’s just that we’re seeing convergence. And this I think is pretty important. [distinction] say, says Carra. In low-income countries, “rural children may still be a little behind and so there is still scope to keep thinking about targeting vulnerable populations where resources can be used more efficiently. It also brings us back to the fact that we have to dig a little deeper to understand who exactly are the kids who are falling behind.”
Bixby and her colleagues are also working to better understand and focus on where the poorest live and how to support them. She hopes that this data will help to understand where to implement policies and programs that support growth and development.
“Even in rich countries, the inequality that we see in cities can be very large,” she says. “This is not surprising, but while cities can offer many opportunities for good health, these opportunities do not seem to be available to everyone. Those who miss these opportunities are often the most disadvantaged people. I think that’s what’s showing up in the data and it’s kind of a warning sign for growing urban inequality.”
Editor’s note (03/29/23): This story was edited after publication to correct the number of decades covered in the study.