TUESDAY, June 17, 2014 (HealthDay News) -- A popular provision of the Affordable Care Act that allows young adults to stay on a parent's health insurance plan up to age 26 may be good for their health and financial security, a large study suggests.

Having that coverage is associated with a 6.2 percentage-point increase in the probability of young adults reporting excellent health and 4 percentage-point gain in mental health, compared with a group of somewhat older peers, the study authors said.

Being enrolled in a parent's health plan may also yield financial benefits. Young adults' annual out-of-pocket spending dropped 18 percent, compared with adults in their late 20s and early 30s.

The study shows that "insurance coverage makes a difference for many types of people, including relatively healthy young adults," said study lead author Dr. Kao-Ping Chua, a pediatrician at Boston Children's Hospital and a Harvard University doctoral candidate in health policy.

Chua, along with Dr. Benjamin Sommers of the Harvard School of Public Health, reported their study findings in the June 18 issue of the Journal of the American Medical Association.

The Affordable Care Act, or Obamacare, as some people call it, requires most health plans that cover children to allow young adults to enroll, too. Adult children may stay on a parent's health plan until age 26.

The "dependent coverage" provision was implemented back in September 2010, and remains one of the least controversial aspects of the very controversial Affordable Care Act. A Senate Republican proposal to repeal and replace Obamacare, introduced this January, retains that element of the law.

Previous studies have shown that allowing young adults to stay on their parents' health plans increases their insurance coverage and access to care. But not much is known about the impact of the Obamacare provision on health and medical spending.

The researchers behind the new study drew up a sample of more than 60,000 people participating in an annual U.S. households survey from 2002 to 2011. They tossed out data from 2010, the year the dependent coverage provision took effect.

That left one year of data from the post-Obamacare period.

The research team followed two groups: young people, ages 19 to 25, and a control group of adults, ages 26 to 34, before and after the coverage provision's implementation. This allowed researchers to filter out any changes affecting the entire health system and to isolate the effects of expanding coverage just to the younger group.

The study linked dependent coverage to a 7.2 percentage-point bump in insurance coverage among young adults, as well as self-reported increases in physical and mental health.

Dr. Robert Fortuna, assistant professor of medicine and pediatrics at the University of Rochester in Rochester, N.Y., said expanding access to health care likely contributed to the increases in health.

Often described as "young invincibles," young adults, in fact, "face many preventable health conditions, and relatively small changes in health care access may have a large impact on overall health," Fortuna explained.

While the study did not detect any statistically significant changes in the use of health services, such as doctor visits and hospitalizations, Chua said this wasn't surprising.

"I think you can make the argument that for a lot of these outcomes you wouldn't necessarily expect a change, because a lot of young adults are healthy at baseline," he said.

Also, the authors did not have access to 2012 data that could have revealed longer-term changes in young adults' use of health services.

In studies by The Commonwealth Fund, a New York City-based research and grant-making group, young adults who enroll in a parent's plan tend to have higher incomes than those who don't enroll.

"This is because young adults with lower incomes are less likely to have a parent with a health plan they can join," said Sara Collins, vice president for the Fund's health care coverage and access program.

Still, the Harvard study suggests that even those who weren't able to join a parent's plan "will realize similar benefits" by enrolling in private coverage through the new Obamacare marketplaces or through the law's Medicaid expansion, Collins said.

More information

The national advocacy group Young Invincibles has details on the dependent coverage provision.