Updated at 1:45p.m. E.T.

Medicare Advantage premiums fell an average of 7% over the past year, according to HHS, even as enrollment rose by about 10%.

Average premiums fell to $31.54 in 2012 from $33.97 in 2011, while enrollment rose to 12.8 million from 11.7 million beneficiaries in the same timeframe, according to figures released by HHS.

At least some of that average premium increase may stem from the continued spread of zero-premium plans in the Medicare Advantage program. Fifty-two percent of Medicare Advantage plans with prescription drug coverage charged no premium in 2011, according to a September 2011 Kaiser Family Foundation analysis of CMS data.

The enrollment numbers should serve to counter criticisms by Republicans that the healthcare reform law would eliminate many such plans because it will reduce payments to them by an estimated $136 billion over the first 10 years that the law is implemented, Obama administration officials said.

“Many people raised fears over and over again that under the Affordable Care Act beneficiaries would see their Medicare Advantage options shrink and their premiums rise,” HHS Secretary Kathleen Sebelius said in a call with reporters. “Instead we are seeing just the opposite.”

However, Jonathan Blum, deputy administrator at the CMS, acknowledged during the media call that the number of Medicare Advantage plans available for beneficiaries to choose from continues to shrink. Many of those options, he said, were little different.

“Prior to the Affordable Care Act, plans sponsors would offer four or five plans in the same marketplace with very few differences and benefit offerings,” Blum said. “We’ve worked very hard with the industry to kind of narrow it down to have the best possible choices offered by the sponsors.”

Despite that, the acknowledged decrease in the number of plans overall, beneficiaries continue to have the choice between an average 26 Medicare Advantage plans, the same number the White House reported in February 2011.