Assets under management in the mutual fund industry totaled $13 trillion in December, up $1.8 trillion from the same period a year before, according to New York-based Strategic Insight.

Despite these gains, many fund executives are wary about unforeseen aftershocks from the subprime crisis and tighter lending markets, but they remain cautiously optimistic about the future.

Investment in Asian stocks and bonds nearly doubled last year and is expected to surpass $450 billion this year.

“Positioning one’s portfolio so it participates in global wealth creation, not just the U.S. , remains a key consideration for long-term investors,” said Avi Nachmany, director of research for Strategic Insight.

The number of U.S. households with mutual funds increased for the fourth consecutive year. Investors have about $3 trillion of their retirement funds invested in the stock markets, with about half in mutual funds, according to the Investment Company Institute.

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