Most people think of height as a personal trait that has little to do with their health, much less the society around them. But when scientists collect height data for entire populations, intriguing patterns appear. According to a new study, American men were the third-tallest people on the planet a century ago but now rank 37th in the league table of tall—and some researchers think height would be a better tool for measuring sustainable human development levels than the standard economic indicators.
The study, published last week in eLife, was led by researchers at Imperial College London in collaboration with the World Health Organization and almost 800 researchers around the globe. They combined data from 1,472 sources such as epidemiological studies and population health surveys, which included height measurements for 18.6 million adults born between 1896 and 1996.
The team produced average-height estimates for 18-year-olds in 200 countries, spanning the years 1914 to 2014. The researchers found that Dutch men are tallest today, followed by those from Belgium, Estonia and Latvia. Latvian women rank highest in stature, with Dutch, Estonian and Czech women also standing tall. The biggest increase among women was in South Koreans, who have shot up a whopping 20.2 centimeters, whereas Iranian men have grown the most, adding 16.5 centimeters. The gap between the tallest and shortest women has stayed constant, at 20 centimeters and the gap between men has increased by four to 23 centimeters.
Height is still increasing in some Latin American and southern European countries but it has plateaued in many other places in the last few decades. North America was the first to stop growing, around 30 or 40 years ago, and the U.S. has experienced the smallest increase of any high-income country (five centimeters for women, six centimeters for men). Other countries that have leveled off include the U.K. and Japan.
Height is one of the most heritable human traits, but the researchers say environment also plays a role. “Genetics doesn't change so quickly, so if you see a change over 100 years, it has to be environmental,” says the new study’s co-lead author, Mariachiara Di Cesare, now at Middlesex University London. A major influence on height, especially early in life, is nutrition. Another is childhood infections, so clean water and health care are also important.
Put simply, the idea is that genetics determines a range and environment determines where people end up within it. “Each of us has a genetic potential height, so if the nutrients you get in early life aren’t enough, you don't reach that potential,” Di Cesare explains. In turn, height has been associated with changes in risk of certain diseases. Taller people have a lower risk of heart disease but greater one for some cancers including colorectal, breast and ovarian. On balance though, taller is better. “There's good evidence that taller people, on average, live longer, and a big part of that is due to lowered risk of cardiovascular diseases,” senior author Majid Ezzati told reporters during the EuroScience Open Forum conference in Manchester, U.K., where the findings were announced.
The team compared changes in height with changes in risk of dying between ages 50 to 70, finding that countries that had grown most tended to have declined most in risk of premature death. “In the case of men, countries that gained 10 to 12 centimeters in height had about [a] 20 to 30 percent decline in risk of premature dying,” Ezzati said. “Slightly smaller for women, about 10 to 20 percent, but those are big changes.”
Another factor that could affect average height is immigration, but not all countries with high immigration show the same pattern as the U.S. “There are other countries where immigration is high, like Canada, Australia or the Netherlands, and Netherlands ranked first” in height, Di Cesare says. More tellingly, the findings are consistent with earlier studies that explicitly accounted for immigration. Economic historian John Komlos, a visiting professor at Duke University, published a study in 2007 that excluded immigrants. It also found that the U.S. plateaued earlier—and shorter—than many European countries. “The west European welfare state creates the best conditions for optimal growth of the human organism,” says Komlos, who was not involved in the Imperial College–WHO study. “That's a major finding of this research.”
Komlos has also studied obesity—and has found that not only are Americans falling short, they are also getting wider. Given there is no shortage of access to food in the U.S., studies like these suggest that, in high-income countries, it is not quantity so much as quality of food that matters. Komlos also suggests that financial inequality matters across the board because rich children increase in height less than poor children decline—so more inequality may mean a shorter population, especially if there are more poor children. “The U.S. has fallen behind because of the delivery of medical care; a large segment of the population is uninsured, and doesn't get good nutrition and health care early in life,” Komlos says. “The U.S. has the greatest poverty rate in the developed countries: about 20 percent of children grow up in poverty; in the Netherlands it's probably about half that.” Height has also been linked to educational attainment and higher incomes and Komlos says links to both health and wealth are consistently found. “There's no exception: higher income—taller population; higher mortality rate—shorter population; more inequality—shorter population,” he says. “It's undeniable.”
The new study contributes data on many more countries, and findings include the fact that people in south Asian countries (such as India and Bangladesh) have stopped growing at shorter heights than east Asian countries (Japan and South Korea) whereas parts of sub-Saharan Africa (Uganda and Sierra Leone) and the Middle East are declining in height. This is likely due mostly to poverty but also to the disruptive effects of conflict—a situation different from that in the U.S. “It's two completely different aspects of lack of nutrition,” Di Cesare says. “In one case, it's poverty and no access to food with the right nutrients. In the other, it's quantity but not nutrients plus inequalities.”
The authors assert that the study shows the potential of using height as an indicator of human development. It is easily measured and provides a link between early-life experiences, health, longevity, education and earnings. Komlos agrees: “GNP [gross national product] is used as a welfare indicator almost as a fetish in our culture, but it's inadequate,” he says. “GNP doesn't have anything to say about inequality; height does. GNP has nothing to say about children; height does. So it reaches the part of the population that's left out of GNP measures,” he says. “That's why height is such a useful supplementary indicator, because it's a better reflection of the quality of life.”