While more U.S employers now offer flu shots, check ups and other workplace health initiatives, about a third are shifting costs onto workers, a new study shows.

A recent analysis of 5,500 workplace benefit plans found that 68 percent of employers offered wellness programs, according to Olathe, Kan.-based Compdata Surveys. Of these employers, nearly 36 percent have increased costs borne by workers.

The study found that employers in the Midwest were the most likely to offer wellness programs, while those in the West were the least likely.

Flu shots and immunizations were the most widely offered benefits.

"Health insurance premium costs have been increasing at a lower rate for the last five years, but employers and employees alike continue to be affected," said Theresa Worman, vice president of business development at Compdata. Despite the recent shift, the current number of employers offloading health costs on employees is still lower than in 2005, when nearly 43 percent of businesses raised employee premiums, Worman said.

In a survey conducted earlier this year by the Kaiser Family Foundation, 40 percent of employers said they're planning to raise the amount employees paid for health insurance. This year, the average annual premiums for employer-sponsored health insurance plans was $4,704 for single coverage and $21,680 for family coverage, up five percent from last year, the Menlo Park, Calif.-based health-care policy research firm reported.