NEW YORK (TheStreet) Americans are increasingly investing in foreign stocks, and millennials are leading the way.

The generation born from 1980 to 2000, whose estimated population of 92 million makes it the biggest in U.S. history, consistently invested more in international stocks than any other age group from 2005 to 2011, according to a new study by the National Bureau of Economic Research. The gains occurred despite rising appetites overall for foreign investments.

"Younger cohorts [are] investing more internationally than older ones, and each cohort [is] investing more internationally over time," says the June-dated report titled, "Who is Internationally Diversified."

Older people are consistently less internationally diversified than younger ones, according to the report. Millennials held almost one-fourth of their equity holdings in non-U.S. stocks by the end of 2011, based on analysis of investments by 3.8 million individuals in 401(k) retirement plans. That was higher than any of the other age groups studied, with the oldest, those born before 1950, holding less than 15% by the end of 2011.

In addition, the study found that all age groups saw a steady increase in the allocation toward non-U.S. stocks over the past few years.

The authors of the study do caution that investments in 401(k) plans may not be the whole story for everyone.

"Because we only have data on the 401(k) allocations, which for many individuals may not represent their full investment portfolio, it is conceivable that some people under- invest in international equity in their 401(k) plan, but have international allocations elsewhere," the report says.

Still, the only investments many people have are in their 401(k) plans, and the trends do in some ways reflect the changing state of the world.

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