The Dutch, thought to be the world's tallest people, seem to have stopped growing. Average heights have increased scarcely or not at all since 2001, the Central Bureau for Statistics said in a new study.

From the early 1980s to 2000, the height of the average Dutch men increased by more than an inch, to just under 5 foot, 11 inches in 2000. But since 2001, heights have been unchanged at slightly above 5'11".

Dutch women gained slightly to around 5'6", the agency said.

Study author Frans Frenken speculated the Dutch may be reaching a natural peak.

"Previous gains are usually attributed to improvements in nutrition and health care," he said. "If they've reached their optimum level then there's not much more you can do."

International studies have found the Dutch to be the world's tallest people, usually ascribing that to wealth, nutrition, genetics, and the country's universal health care system.

John Komlos, of the University of Munich, who has studied height differences between the U.S. and the Netherlands, said "the results are not surprising."

"I've been saying for some time now that the Dutch are not going to increase in height much: they've probably reached their genetic limit," he said. "Nobody knows for certain, and I'm just guessing."

He says the most recent data show Dutch boys reaching adulthood are, on average, over six feet. That's 2.2 inches taller than their American counterparts, a gap that has been increasing since World War II.

Frenken based his figures on his agency's annual poll of around 10,000 people, adjusting them slightly to reflect people's tendency to exaggerate their height.

An influx of immigrants has lowered the average Dutch height slightly. Male immigrants are 2.4 inches shorter, decreasing the national average by less than half an inch.

He said he couldn't predict whether children of immigrants would be as tall as other Dutch. "We just don't have the data," he said.