Science has long presumed that children living in cities grow faster and healthier than rural kids—but that trend has flipped over the past three decades, a new study suggests. A global study published Wednesday in Nature found that the average height of urban children and adolescents ages 5 to 19 is now slightly shorter than that of their peers in rural areas in most countries—notably in wealthy countries such as the U.S., the U.K. and France.
“Where we’ve historically seen a quite clear benefit for living in cities, that benefit has been slightly diminished over time,” says study co-author Honor Bixby, a population health and epidemiology research fellow at the University of Essex in England. “But it can be viewed as a positive in that rural height is really catching up.”
Researchers are still trying to tease apart exactly why this is happening, however.