LONDON • Dutch men and Latvian women are the planet's tallest people but Iranian men and South Korean women have grown the fastest in the last century, according to the largest-ever study of people's height around the world.
Americans, once among the world's tallest people, have dropped from having men and women at third and fourth in the global height rankings 100 years earlier, to placing 37th and 42nd respectively in 2014.
The 800-strong research team, led by scientists at the Imperial College London, used data from various sources including health and nutrition population surveys and epidemiological studies. The scientists used these to generate height information for 18-year-olds in 1914 through to 18-year-olds in 2014.
They found that Iranian men have gained an average of 16.5cm in height, and South Korean women 20.2cm. The study also found that Dutch men are the tallest, at an average height of 1.825m, and Latvian women are the tallest, at an average height of 1.7m.
Men from Timor Leste were the smallest worldwide in 2014, at an average height of 1.6m, while Guatemala women were the smallest, at an average height of 1.49m.
The research, published in the journal eLife, also found that some nations have stopped growing over the past 30 to 40 years, despite having spurts at the start of the century studied.
The United States was one of the first wealthy countries to plateau, followed by others including Britain, Finland and Japan.
Meanwhile, people in Spain and Italy and many countries in Latin America and East Asia are still gaining in height.
In contrast, some nations in sub-Saharan Africa, North Africa and the Middle East have seen average heights decline over the past three to four decades.
"This study gives us a picture of the health of nations over the past century," said Imperial professor of public health Majid Ezzati. He said the findings underlined the need "to address children and adolescents' environment and nutrition on a global scale".
Human height is strongly influenced by nutrition and environmental factors. Children and teens who are better nourished and live in better environments tend to be taller.
Research also suggests that a mother's health and nutrition during pregnancy may play a role in how tall her children grow.