Ezzati said that recent immigration from Latin American nations, which in general are shorter, do not explain the leveling off of the American male (and female) height.
"Immigration is one hypothesis, but the quality and equity of nutrition in America" is the cause, he said.
Taller people don't just get noticed in a crowd. They also have a greater life expectancy, a lower risk of cardiovascular and heart disease, and higher education and income.
A 2004 study found someone who is 6 feet tall earns, on average, nearly $166,000 more during a 30-year career than someone who is 5 feet 5 inches--even when controlling for gender, age and weight.
Shorter women also have a more health risks during pregnancy, according to the researchers, although taller women have a higher risk of breast and ovarian cancer.
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Because nutrition, health and height are linked, the scientists said they are concerned that the average height of young women and women has dropped by more than two inches in the last 40 years in sub-Saharan nations of Sierra Leone, Rwanda and Uganda.
The research also revealed some unusual patterns. Iranian men have grown an average of 6.5 inches over the past century, while South Korean women grew an average of nearly eight inches, said James Bentham, a statistician at Imperial College.
The study also found that the average height difference between men and women has remain constant over time – 4.3 inches among 18 year olds in 1914 compared to 4.7 inches among the same group in 2014.
The research team, which included almost 800 scientists and was in collaboration with the World Health Organization, used data from a wide range of sources, including military conscription data, health and nutrition population surveys, and epidemiological studies. They used these to generate height information for 18 year olds in 1914 (who were born in 1896) through to 18 year olds in 2014 (who were born in 1996).
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Solveig Cunningham, associate professor of public health at Emory University, has studied childhood health in both the U.S. and abroad. She wonders if the connection between poor nutrition and height is as clear as the authors believe.
"There are still a few places where war or famine has temporarily disrupted nutrition," Cunningham said in an e-mail to Discovery News. "While in the U.S. we do worry about intake of high-calorie/low nutrient foods and "overnutrition" leading to overweight, and some evidence of food insecurity, I have not seen evidence of increases in underweight or stunting in the U.S."
Cunningham noted that the height records were drawn from U.S. military records. A century ago, males were drafted, but today the population of recruits is from a less diverse pool.
"A more diverse population due to migration may also be relevant," she said. "It is not just about genes, but also about people's early-life exposures -- so it is possible that the U.S. could have, through migration, more people who were relatively more malnourished in childhood than the U.S.-born population than in earlier cohorts."