The laws are meant to help those over 18, who typically outgrow their parents' plans but have trouble getting full-time jobs with health coverage after high school.

The authors say even though people between 19 and 29 years old make up 17 percent of adults under age 65, they account for almost 30 percent of the uninsured.

"Ultimately, these state laws, and the provision within the Affordable Care Act (ACA), help provide secure footing just when these young people are starting off on their own," said Dr. Alexander Blum, the study's lead author and a health policy researcher at Mount Sinai School of Medicine in New York.

In September 2010, the federal government enacted a provision that allows young adults to stay on their parents' private insurance plans through age 26.

For their analysis, Blum and his colleagues looked at 19- to 23-year-olds living in states that passed laws extending their parents' coverage in 2005 or 2006, but did not include Massachusetts because it mandated health insurance.

Blum's team used a national survey conducted by the Centers for Disease Control and Prevention (CDC) that asked about access to care.

In the years before the state laws' enactment -- 2002 to 2004 -- about 62 percent of the survey respondents could identify a primary doctor and about 77 percent had had a physical exam in the last two years.

A few years down the road - in 2008 to 2009 -- the researchers observed modest improvements in those numbers to about 66 percent and 81 percent, respectively.

In the states that extended coverage, about 20 percent of the young adults reported during the earlier study period that they went without care due to cost. That number decreased to about 18 percent between 2008 and 2009.

Overall, those were modest improvements over states that did not pass laws extending coverage. And the number of young adults with insurance coverage rose about half a percentage point regardless of whether the state enacted a law or not.

Writing in the journal Pediatrics, Blum and his colleagues suggest this can be explained by the laws encouraging young adults to move to their parents' plans from less comprehensive coverage.

The authors cannot say for certain whether the differences were caused by the new state laws because the CDC's survey did not ask whether the young adults were covered under their parents' plan.

Alan Monheit, a health policy researcher at the University of Medicine & Dentistry of New Jersey, told Reuters Health that despite limitations of the new study, he believes the insurance extension in the federal law will lead to visible benefits.

"I think that we will see an improvement in coverage with the ACA, and I think the reason is that the ACA now ropes in the self-insured plans," said Monheit.

Self-insured plans are funded by employers and make up a large part of the U.S. health insurance market. The plans were typically exempt from the state laws that extended coverage to adult children, but are included under the federal law.

The inclusion of self-insured plans is just one of the differences between the state and federal laws, Blum's team notes, and they are the reason the ACA's impact will be much greater than that of the state laws.

"Even in the states that had a similar provision, they were much narrower," agreed Sabrina Corlette, a health policy researcher at Georgetown University's Health Policy Institute who was not involved in the new study.

Corlette told Reuters Health that many of the state laws limited their insurance extensions based on whether the young adult was a student or married. The federal law expanded coverage in those categories.

In December 2011, the CDC reported that 2.5 million Americans between 19 and 25 years old were able to get health insurance thanks to the ACA.

The U.S. Department of Health and Human Services said the provision increased the number of insured young adults in that age group to 73 percent in June, from 64 percent.

SOURCE: bit.ly/xGkVy4 Pediatrics, online February 13, 2012.

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