Under the Patient Protection and Affordable Care Act, signed into law in March 2009, 2.5 million more young adults have gained health insurance coverage, according to new figures released Dec. 14 by the U.S. Department of Health and Human Services.

A provision in the federal healthcare reform law allows adult children to stay on their parents’ health insurance plan through age 26. The new policy took effect in September 2010. Data from the National Health Interview Survey shows that from September 2010 to June 2011, the percentage of young adults aged 19 to 25 covered by a private health insurance plan increased significantly – from 64 percent to 73 percent, translating to 2.5 million young Americans.

"Moms and dads around the country can breathe a little easier knowing their children are covered,” HHS Secretary Kathleen Sebelius said in a statement.

Data from the first three months of 2011 showed that nearly one million more young adults had insurance coverage compared to a year ago. Among adults aged 19 to 25, the percentage of uninsured individuals decreased from 33.9 percent – or 10 million – in 2010 to 30.4 percent – or 9.1 million – in the first three months of 2011.

Traditionally, young adults have been less likely than older adults to purchase a health insurance plan or opt into one through their employer due to cost reasons and because young adults typically use far fewer healthcare services than older adults.

For Americans under age 24, the unemployment is around 16.7 percent, more than twice the rate for workers 25 and older. This means many young adults do not even have the option of opting into an employer-sponsored healthcare plan.

Especially for young adults with chronic or other complex diseases, the Affordable Care Act measure has prevented them from being dropped from their parents’ coverage. Once young adults turn 26, the Affordable Care Act also makes it illegal for a health insurance plan operating in the United States to deny coverage to anyone, regardless of a pre-existing condition.

The data from the June 2011 National Health Interview Survey released Dec. 14 include the first official comparisons of trends between adults ages 19 to 25 and slightly older adults, ages 26 to 35.

The percent of adults aged 26 to 35 with insurance coverage was stable, at 72 percent, from September 2010 to June 2011, and coverage rose only among those adults affected by the policy. This comparison makes it clear that the increase in coverage among 19- to 25 year-olds can be directly attributed to the Affordable Care Act’s new dependent-coverage provision. Additionally, the coverage gain for young adults was entirely due to an increase in private coverage, with no change in Medicaid coverage during this period.

The trends in the NHIS data are consistent with estimates from other earlier surveys that have shown an increase in the number and percentage of young adults 19 to 25 with health insurance coverage. Specifically, the Census Bureau and the Gallup-Healthways Well-Being Index Survey, as well as the NHIS release of data through March 2011, reported similar trends through early 2011.