Twice as many people have enrolled in consumer-directed health plan (CDHP) in the last two years, as more companies offer the option.

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

The survey found that companies with at least half of their workforce enrolled in a CDHP had a two-year median cost trend of 3.6%, almost half that of companies without a CDHP. Overall, companies with a CDHP experienced a two-year cost increase trend of 5.5% versus 7% for companies without a CDHP.

The results are a good sign for the health insurance industry, which has been encouraging employers to offer the option as a means to reduce their health care costs. But the adoption by employers and employees has been slow, especially in areas of the country, including the mid-Atlantic states and parts of the North East, where pricing pressure had not been as pronounced, experts say.

“A CDHP offers a way for companies to control costs while increasing employee accountability for health care decisions,” said Ted Nussbaum, Watson Wyatt’s director of group and health care consulting in North America, in a statement.

For insurers, the carrot is that people who participate in CDHPs tend to become more involved in their health care decisions and the costs associated with their actions.

“The participants in a consumer-oriented model must be more familiar with the system and have a deeper understanding of their options,” Nussbaum said. “But encouraging employees to adopt healthy behaviors and manage their health proactively is no easy task.”

Nearly half (47%) of the 453 large U.S. employers that participated in the survey now offer a CDHP, an increase from 39% in 2007 and 33% in 2006. By the end of this year, 54% of companies plan to offer a CDHP, researchers found. 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.

Exactly 27% of companies offer CDHPs with a health savings account (HSA), while 24% offer a health reimbursement account (HRA). HSAs appear to be favored for 2009, with 9% likely to add them, compared to 3% expecting to add an HRA, the research found.

As adoption rates climb, employee enrollment also continues to rise. Fifteen percent of employees at organizations that offer CDHPs are currently enrolled in such plans, up from 8% in 2006 and 10% in 2007.

Just 6% of companies report total enrollment in a CDHP, but that number is expected to rise to 9% this year, based on the responses of participating companies.