WASHINGTON, March 13 (UPI) -- The number of U.S. workers who enrolled in consumer-directed health plans, or CDHP, has nearly doubled over the last two years, a study said.

Health cost increases for companies with high CDHP enrollment are roughly half those facing companies offering only traditional health coverage, an annual survey conducted by Watson Wyatt and the National Business Group on Health found.

Forty-seven percent percent of the 453 large U.S. employers that participated in the survey currently offer a CDHP, an increase from 39 percent in 2007 and 33 percent in 2006.

By 2009, 54 percent of companies plan to offer a CDHP, the National Business Group on Health said.

A CDHP is a high-deductible plan offered with a personal account that can be used to pay a portion of medical expenses not covered under the plan.

Fifteen percent of employees at organizations that offer CDHPs are currently enrolled in such plans, up from 8 percent in 2006 and 10 percent in 2007. Six percent of companies report 100 percent enrollment in a CDHP.

Companies spent an average of $7,211 on healthcare per employee in 2007, the study said.