Shares of several big health insurers fell Monday as jittery investors dumped equities en masse because of new fears about the economic stability of Europe.

Big U.S. managed care companies tend to invest almost entirely at home, particularly in conservatively in treasuries and high-grade corporate bonds, so their direct exposure to European financial problems is limited. Industry watchers believe insurer stocks are losing ground because people are trading equities for more conservative fixed-income investments, not because of any direct concern about the effects of the European debt crisis on U.S. health care.

"I would say that's probably been the driver more than anything," Morningstar analyst Matt Coffina said.

Yet health stocks can fall if there is pessimism over the economy. If employers start cutting jobs again, fewer people will be covered by employer-sponsored health insurance.

However, Jefferies analyst David Windley said it is premature for those concerns to move health stocks.

Shares of UnitedHealth Group Inc., the largest U.S. insurer, fell 2.4 percent, or $1.34 to $54.07 in afternoon trading, while WellPoint Inc. dropped 65 cents to $61.29. Aetna Inc. fell 2.4 percent, or 89 cents, to $36.77, Cigna Corp. was down 63 cents to $41.05, and Humana Inc. fell 2 percent, or $1.48, to $72.14.

Meanwhile, the Standard & Poor's 500 index and the Dow Jones industrial average both slid more than 1 percent.

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