Being tall has its perks — and it has nothing to do with machismo or the size of Donald Trump’s hands.

Taller people have been found to earn more money, studies show, and find greater success in school. They are less likely to have a difficult pregnancy or develop heart or respiratory diseases. Those with extra inches tend to live longer.

Research shows that this particular physical attribute is largely predetermined by genetics but can be influenced by environmental factors. A handicapped economy, poor diet or vast inequality can stunt the growth of entire countries.

A recent study, published in eLife, explores how these factors may have affected the height of the world’s population during the last 100 years, analyzing who grew, who shrunk, by how much and, most importantly, why.

South Korean women and Iranian men have hit the greatest growth spurt, sprouting by an average of nearly eight and six and a half inches, respectively, since 1896. But in sub-Saharan Africa and South Asia, the people hardly budged and some evidence suggests that adult height has decreased since the 1960s.

And in the United States, where its citizens once ranked the third and fourth tallest, both men and women had the smallest gain in height of any high-income country and plateaued first, followed by Britain, Finland and Japan. Now, American women rank 37th and the men slipped to 42nd. In the United States, height increased less than the worldwide median, but BMI ballooned significantly.

It has to do, largely, with nutrition.

“I think one thing that one should keep in mind in these studies is that height is a useful indicator of how nutrition and health is developing and that these are closely related to the overall economic development [of a country], ” Alexander Moradi of the University of Sussex, who was not involved in the study, told the Guardian.

A more severe example of the potentially troubling ties between nutrition and height unfolded in Africa during the peak of the economic troubles in the 1980s, the Guardian reported. Amid the mayhem, many children and teenagers, perhaps malnourished since birth, had their ability to grow to their tallest height potential impeded.

“How tall we are now is strongly influenced by the environment we grew up in. In turn, our height affects both our life expectancy and our health as adults,” James Bentham, a co-author of the research from Imperial College, London, told the Guardian. “If we give children the best possible start in life now, they will be healthier and more productive for decades to come.”

Of the people born in the year 1896, those in Asia and Central and Andean Latin America were the shortest. The tallest people a century ago lived in central and northern Europe, North America and some Pacific islands, according to the study. Of all the people studied during the 100-year period, men born in the Netherlands in the late 20th century were the tallest. And, during the same period, Latvian women were the tallest.

The study team, made up of 800 researchers, worked with the World Health Organization to analyze thousands of previous health and nutrition population surveys, epidemiological studies and military conscription figures, reported Reuters. They studied people born between 1896 and 1996 and began analyzing their information once the subjects turned 18, creating a database that spanned 100 years.

“This study gives us a picture of the health of nations over the past century,” Majid Ezzati, an Imperial professor of public health, told Reuters.

The findings, he said, show the need “to address children and adolescents’ environment and nutrition on a global scale.”