The Korean peninsula gives history something rare: a natural experiment.
Draw a line at the 38th parallel and, on both sides, you have people who until 1945 shared a common population history and broadly similar ancestry. Then the country split, and two very different childhood environments developed.
Two generations later, the bodies had grown apart. A study by Daniel Schwekendiek and Sunyoung Pak noted that in 1997 South Korean preschoolers were 6 to 7 centimetres taller than children the same age in the North, and the gap was about 8 centimetres by 2002.
Related work by Schwekendiek put the difference at up to 13 centimetres shorter and up to 7 kilograms lighter for preschool children raised in the North. Broadly shared ancestry, sharply different conditions.
A note before going further: we are not clinicians, nutritionists, or growth researchers. What follows is reading and reflection on one large study and the work around it, not health advice. The research here is observational, and patterns across a whole population say little about any one person’s height or health.
What the 2016 study measured
The headline number comes from a large piece of work. The NCD Risk Factor Collaboration reanalysed 1,472 population-based studies with measured heights from more than 18.6 million adults, producing estimates for 200 countries and for people born between 1896 and 1996. Published in eLife and coordinated by Imperial College London, it created a century-long global map of adult height.
Its standout entry is South Korea. South Korean women gained more than any other female population, rising 20.2 centimetres, from roughly 142 to 162 centimetres between the 1896 and 1996 birth cohorts. The largest gain for men was among Iranian men, at 16.5 centimetres. For scale, the same data shows British men and women growing around 11 centimetres, and American women about 5.
Majid Ezzati, who led the research, treated the whole thing as a health record, not a curiosity. “This study gives us a picture of the health of nations over the past century,” he said, adding that some nations’ average height “may even be shrinking while others continue to grow taller.” That is the useful way to read the Korean number. It isn’t really about height alone.
The role of the first few years
The Korean comparison does not make the populations genetically identical, but it shows how strongly living conditions can influence growth. The height study itself notes that although height is highly heritable, differences between populations are believed to be largely environmental.
Nutrition researchers pay particular attention to the first 1,000 days, from conception to a child’s second birthday, because poor nutrition and repeated infection in that period can impair linear growth. Adult height is not fixed by age two, and children continue growing through childhood and adolescence. Some catch-up can occur, but the World Health Organization describes established stunting as “largely irreversible”, which is why the earliest years matter so much.
Why South Korea ran the record
Put those ideas together and South Korea’s record starts to make sense. This was a country that changed the conditions surrounding childhood with extraordinary speed.
A woman born in South Korea in the 1990s entered a high-income, industrialized society with far better food security, sanitation and healthcare than the generations born under Japanese occupation or amid the Korean War. The World Bank records South Korea’s rise from a gross national income per person of about $67 in the early 1950s to a modern high-income economy; over $36,000 in 2024.
Each new wave of children encountered better conditions than the last, and average adult height rose with them.
North Korea provides the stark comparison. The country suffered severe food shortages in the mid- and late 1990s, and a 1999 report cited by the FAO found moderate or severe stunting in about 62 per cent of surveyed children. The bodies recorded the difference in living standards without anyone intending them to.
What a 20-centimetre gain is and isn’t
Being tall is not a virtue, and being short is not a failing. At population level, average height is a rough record of foetal growth, childhood and adolescent nutrition, infection burden and living conditions. It does not diagnose the health of an individual.
That is why the flat and falling lines in the same data are as revealing as South Korea’s climb. In some sub-Saharan African countries, average height fell by as much as 5 centimetres over 40 years. Wealth is no guarantee of continued gains: American men and women slid from third and fourth place to 37th and 42nd over the century as US height gains levelled off while other countries continued to rise.
Ezzati argued that the findings confirmed an urgent need to improve children’s and adolescents’ nutrition and environments worldwide and give them the best possible start in life.
The South Korean figure is, in the end, a four-generation letter written in bone: each woman’s height a note about the world in which she grew. The gains are heartening. The more sobering entries are the populations where the line went flat or bent downward, because a stalled height curve can signal that childhood conditions stopped improving, or became worse.
