(Story updated at 2:45 p.m. ET Wednesday, Dec. 14.)

The Obama administration touted 2.5 million young adults gaining employer-provided health insurance coverage through provisions in the 2010 healthcare overhaul, but companies are worried such provisions accelerate the rising cost of coverage.

The coverage increase primarily stems from a provision of the Patient Protection and Affordable Care Act that allows young adults to stay on their parents' insurance plans from 19 through 26, according to an HHS report. The policy took effect in September 2010 and was generally implemented among insurance policies that took effect in January.

“Thanks to the Affordable Care Act, 2.5 million more young adults don't have to live with the fear and uncertainty of going without health insurance,” HHS Secretary Kathleen Sebelius said in a news release.

The reported increase is significantly higher than the 1 million young adults who HHS officials said earlier this year gained coverage under provisions of the law, based on data from the National Health Interview Survey for the first three months of 2011. The greater increase was identified when the data collection period was extended through the first six months of 2011.

But that laudable achievement comes at the expense of increased premiums for all privately insured workers and their employers, which generally pay the majority of such costs, an employer advocate said.

“It basically increases the cost of employer-provided coverage without an equivalent offset, so to speak,” Helen Darling, president and CEO of the National Business Group on Health, said in an interview.

Her not-for-profit group represents 338 of the nation's largest employers and estimates the young-adult coverage and other insurance mandates have contributed a full percentage point to the 2011 insurance cost increase. The Kaiser Family Foundation's annual insurer survey estimated the young-adult coverage mandate and mandated coverage of preventive care together comprised up to 2 percentage points of the 9% increase in 2011 insurance premiums.