WASHINGTON (AP) — Young adults trying to get traction in a tough economy are getting a welcome assist: the new federal health care law has markedly improved their access to health insurance.

The number of young Americans ages 19-25 lacking health insurance has shrunk by 2.5 million since President Barack Obama’s health care overhaul took effect, the administration announced in an analysis released Wednesday.

That drop is 2½ times as large as the decline indicated by previous government and private estimates from earlier this year, which showed about 1 million had gained coverage.

The improvement comes even as the uninsured rate stayed basically stuck for those a little older, ages 26-35.

Under the health care overhaul, adult children can stay on a parent’s plan until they turn 26, a provision that has proven popular in an otherwise divisive law.

Health and Human Services Secretary Kathleen Sebelius said the numbers show the law is making a big difference for families with adult children.

“Many of them gained coverage earlier this spring, meaning the law was there for young people as they graduated from college or high school and began their careers,” she said.

Administration officials said there are a couple of reasons for the better-than-expected result.

First, there is more data available now than earlier this year. Secondly, analysts are slicing the numbers more precisely than the government usually does.

The health care law’s main push to cover the uninsured doesn’t come until 2014. But the young adults’ provision took effect last fall, and most workplace health plans started carrying it out Jan. 1. Since then, families have flocked to sign up adult children making the transition to work in a challenging environment.

The overall fate of Obama’s law remains uncertain, with the Supreme Court scheduled to hear a constitutional challenge next year, and Republican presidential candidates vowing to repeal it. But this provision seems to have gotten a seal of approval from consumers.

“The increase in coverage among 19- to 25-year-olds can be directly attributed to the Affordable Care Act’s new dependent coverage provision,” said the HHS analysis.

Using unpublished quarterly statistics from the government’s ongoing National Health Interview Survey, analysts in Sebelius’ policy office determined that nearly 36 percent of those age 19-25 were uninsured in the third calendar quarter of 2010, before the law’s provision took effect.

That translates to more than 10.5 million people.

By the second calendar quarter of 2011, the proportion of uninsured young adults had dropped to a little over 27 percent, or about 8 million people.

The difference — nearly 2.5 million getting coverage — can only be the result of the health care law, administration officials said, because the number covered by public programs like Medicaid went down slightly.

Overall, nearly 30 million Americans are ages 19 to 25.

“From September 2010 to June 2011, coverage rose only among those adults affect by the policy,” said the HHS report.

The National Center for Health Statistics has documented a broadly similar trend in its official publications, only it’s not nearly as dramatic.

Administration officials said those statistics did not focus on the change from calendar quarter to calendar quarter, as does the new HHS report. Instead, they pool data over longer time periods, and that has the effect of diluting the perceived impact of the law, officials said.

Traditionally, young adults have been more likely to be uninsured than any other age group.

Some are making the switch from school to work. Others are holding down low-wage jobs that don’t usually come with health care. And some — termed the “invincibles” — pass up job-based health insurance because they don’t think they’ll use it and would rather get extra money in their paychecks.

Other early coverage expansions in the health care law have not worked as well, including a special program for people with health problems turned away by private insurers. Many applicants found the premiums unaffordable.

Young adults are less expensive to cover than people who are middle-aged, and many companies have spread the extra premiums among their workers. Benefits consultant Delloite LLP has projected additional health plan costs in the range of 1 percent to 2 percent for covering young adults.

Before the health care overhaul, families with adult children faced a hodgepodge of policies. Some health plans only covered older children while they were full-time students. Others applied an age cutoff.

Copyright 2011 The Associated Press.