The Dutch, thought to be the world's tallest people, appear to have stopped growing, the national statistics agency said Monday.

Growth rates for men and women have increased scarcely or not at all since 2001, the Central Bureau for Statistics said in a new study.

The height of the average Dutch male increased by more than an inch from the start of the 1980s, to just under 5 feet 11 inches in 2000.

Since 2001, heights have been unchanged at slightly above 5 feet 11 inches, and women gained a fraction of an inch to around 5 feet 6 inches, the agency said.

Study author Frans Frenken said he had no explanation for the slowdown, but speculated that 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 a combination of national wealth, eating habits, genetics, and the quality of the country's universal health care system.

John Komlos, chairman of the University of Munich's economic history program, 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."

Komlos, who has studied height differences between the U.S. and the Netherlands, says the most recent data shows Dutch boys reaching adulthood are over 6 feet tall, and 2.2 inches taller on average than their American counterparts, a gap that has been increasing since World War II.

Frenken said he based his figures on his agency's annual health poll of around 10,000 people and adjusted them slightly to reflect a tendency known from previous studies for people to exaggerate their height.

An influx of immigrants has lowered the national average height slightly, but the slowdown in growth was observed among the native population, Frenken said. Male immigrants are 2.4 inches shorter on average, decreasing the national average by less than half an inch.