And those height differences translate into real benefits. A number of studies have shown that disease and malnutrition early in life — the same things that limit a person's height — increase a person's chances of developing heart disease and other life-shortening conditions later on. Though tall people are more likely to get cancer, they suffer less mortality overall than short people.

International statistics bear it out. Life expectancy in the Netherlands is 79.11 years; in Sweden it's 80.63. America's life expectancy of 78.00 years puts it in somewhat shorter company, just above Cyprus and a few notches below Bosnia-Herzegovina.

"Obviously America is not doing badly. It's not at the level of developing nations," Komlos said. "But it's also not doing as well as it could."

His latest research paper, published in the June issue of Social Science Quarterly, suggests the blame may lie with America's poor diet and its expensive, inequitable health-care system.

"American children might consume more meals prepared outside of the home, more fast food rich in fat, high in energy density and low in essential micronutrients," wrote Komlos and co-author Benjamin E. Lauderdale of Princeton University. "Furthermore, the European welfare states provide a more comprehensive social safety net including universal health care coverage."

In the United States, by comparison, an estimated 9 million children have no health insurance.

Komlos' most recent data indicate a small uptick in the heights of white Americans born between 1975 and 1983, a suggestion that the gap may finally be closing. But there has been no similar increase among blacks, a suggestion that inequality may indeed play a significant role in the height gap.

In another recent paper, Komlos and Lauderdale also found height inequality between American urbanites and residents of suburbs and rural areas. In Kansas, for example, white males are about as tall as their European peers; it's big cities like New York, where men are about 1.75 inches shorter than that, that drag America's average down.

Now Komlos has started comparing the heights of children to determine at what age Americans begin falling behind their peers across the Atlantic. Not surprisingly, he sees a difference from birth, an observation that suggests prenatal care may be significant contributor factor to the height gap.

But it is unlikely that Komlos will ever find one simple factor to explain why Americans have fallen behind other rich countries in height. In all likelihood it is caused by a combination of things — a little bit health care, some diet, a sprinkling of economic inequality.