For two centuries, Americans were among the tallest people in the world. But researchers say they are now shorter than most Western and Northern Europeans. The Dutch are now the tallest, topping non-Hispanic American whites by almost 3 inches.

Scientists have wondered for a long time why Americans seemed to have stopped growing and why Europeans were getting taller. Researchers from Princeton University and the University of Munich in Germany now have provided some hard figures and suggestions as to why the change. Their article is in the current issue of Social Science Quarterly.

Co-author John Komlos of the University of Munich told the German magazine Der Spiegel: “We surmise that the health systems and high degree of social security in Europe provide better conditions for growth than the American health system, despite the fact that the [American] system costs twice as much. There are also indications that American diets are deficient in several areas.”

Americans were the tallest in the world from colonial times until the middle of the 20th century. Since then, Mr. Komlos and Benjamin Lauderdale of Princeton wrote, Americans have “become shorter (and fatter) than Western and Northern Europeans. In fact, the U.S. population is currently at the bottom end of the height distribution in advanced industrial countries.”

A correlation between wealth and height has long been recognized. So how come the wealthiest nation in the world has been losing height as well as dropping below other industrialized countries in such measures as life expectancy and child mortality? The researchers say one reason may be the drastic differences in the United States between rich and poor. The U.S. average is pulled down by those who struggle just to get by.

While 15 percent of the U.S. population has no health insurance and those on welfare are at the poverty level, say the researchers, European countries enjoy universal health care and a generous social net. As a result, even children dependent on welfare in Europe have a decent living standard.

Mr. Komlos told Der Spiegel that much needs to be done to determine the relationship between social standards and height: “In short, the richest are neither the tallest nor the healthiest. Why that is so must be explained.”

Regardless of this remaining puzzle, Americans’ literal loss of stature must give further urgency to the efforts to reform and improve this nation’s health care system.