People living in states that expanded Medicaid under the Affordable Care Act (ACA) are less likely to be uninsured or struggling with the strain of unpaid medical bills, a new study finds.

The study is the latest to examine the impact of expanding Medicaid, the public health insurance program for low-income Americans.

To date, 31 states plus the District of Columbia have expanded Medicaid under the ACA, also known as Obamacare. States were allowed to decide whether to implement that provision of the health law after a 2012 U.S. Supreme Court ruling made it optional.

"Low-income adults in expansion states do appear to be better off after the Medicaid expansion," said study co-author Laura Wherry, an assistant professor of medicine at the University of California, Los Angeles David Geffen School of Medicine.

By the second year of expansion, fewer low-income adults said they could not afford medical care, compared with their counterparts in non-expansion states, according to the analysis.

Year 2 of the expansion was associated with other improvements, too, the study found. People were less likely to report not being able to afford follow-up care, including seeing a specialist. They were also less likely to skip needed medications or take less medicine to save money.

The study findings appear in the March 9 issue of The New England Journal of Medicine.

Dr. Benjamin Sommers is an associate professor of health policy and economics at the Harvard T.H. Chan School of Public Health in Boston. He, too, has studied the effects of expanding Medicaid.

"This is part of a growing body of research that shows people benefit from expanded health insurance, and that repealing the ACA -- in particular the Medicaid expansion -- would likely lead to millions of low-income adults losing insurance and experiencing worse access to health care," Sommers said.

But Medicaid expansion wasn't perfect, Wherry said.

Compared with non-expansion states, people in states that expanded Medicaid were more likely to delay obtaining care because no appointment was available, or because wait times for appointments were too long.

This suggests a need to address low provider reimbursement rates, she said.

And, contrary to other studies, this new study found no evidence that people's health improved post-expansion. It could be too early to detect such changes, Wherry suggested.

Also, the study relied on patients' self-reported health status, which may not be as informative as objective measures of health gathered from clinical and administrative data, she explained.

Sommers said he wouldn't read too much into that finding. He said there's evidence from at least four other studies "that expanding Medicaid improves patients' perceived health status."

Wherry and her colleagues based their findings on data from four years prior to the state Medicaid expansions and two years afterward. The researchers included states that implemented the Obamacare Medicaid provision during 2014 or 2015. They excluded five states that had already provided Medicaid or similar coverage to low-income adults from 2010 to 2013.

The researchers used data from a nationally representative annual survey conducted by the federal government to assess the effects of the expansion. The sample included more than 60,000 adults, 19 to 64 years old, with family incomes below 138 percent of the federal poverty level.

In year 2 of the expansion, rates of people without insurance were roughly 8 points lower in expansion states compared to non-expansion states. Likewise, rates of Medicaid coverage rose by nearly 16 points, the study found.

And worries about medical bills dropped by nearly 8 points.

"They're less likely to report forgoing care, and they seem better off financially," Wherry said. "It's something to keep in mind as we talk about the future of the [Medicaid] expansion," she said.

Those discussions are already underway.

On Monday, Republicans in the House of Representatives unveiled their long-awaited plan to "repeal and replace" Obamacare.

Among key provisions of the plan: Medicaid would be converted to a state-based block-grant program, with federal funding capped per enrollee and based on how much each state spent on Medicaid in fiscal year 2016.

The 31 states that chose to expand Medicaid would continue to get additional federal funding until 2020. However, funding would be reduced for anyone who tries to enter the program after 2020, or those who leave the program and then come back.

The GOP proposal has been criticized on multiple fronts. On Wednesday, the American Medical Association said the proposal "would result in millions of Americans losing coverage and benefits."