WASHINGTON – Poor Americans in states that have expanded Medicaid through the Affordable Care Act are going to the doctor more often and having less trouble paying for it, new research finds.

At the same time, two years of experience with the expansion offer additional indications that the improved access to care will ultimately improve patients' health, a key goal of 2010 law.

"The effects of expanding coverage will be an unfolding story over time," said Dr. Benjamin Sommers, lead author of the study, published in the journal JAMA Internal Medicine. "But we are starting to see the kind of broad-based improvements that we would expect with better access."

Sommers and other researchers at Harvard University have been tracking the impact of Medicaid expansion by surveying poor residents in Arkansas and Kentucky, both of which expanded Medicaid eligibility, and in Texas, which has rejected the expansion.

Since 2014, the health law has made hundreds of billions of dollars of federal aid available to states to extend Medicaid coverage to poor adults, a population that had been largely excluded from the government safety net program.

Medicaid eligibility historically was limited to certain vulnerable populations, including low-income children, pregnant women, people with disabilities and the elderly. Thirty-one states have opted for the expansion.

But Republican politicians in many red states continue to oppose expansion, arguing that Medicaid is unaffordable and ineffective. GOP presidential nominee Donald Trump has pledged to repeal the law.

The divide between states that have expanded and those that have not is profound, the new research suggested.

In Arkansas and Kentucky, for example, the share of poor adults without health insurance plummeted between 2013 and 2015, from more than 40 percent in both states to 14 percent in Arkansas and less than 9 percent in Kentucky.

In Texas, by contrast, the uninsured rated dropped only from 39 percent to 32 percent.

The new coverage in Arkansas and Kentucky, in turn, dramatically improved poor patients' access to care and relieved financial strains, the surveys showed.

The share of patients in the two states who had trouble paying medical bills fell more than 11 percentage points between 2013 and 2015, while in Texas, more patients reported medical bill problems in 2015 than in 2013.

Survey data from 2014 showed those improvements after just one year of the Medicaid expansion in Arkansas and Kentucky. But with another year of data, researchers noted more evidence that the improved access is also allowing more poor patients to seek recommended medical care.

In 2015, for example, nearly 55 percent of low-income Arkansas residents reported having a checkup in the past year, up from 45 percent in 2013.

In Kentucky, the percentage surged even more, from 46 percent to nearly 60 percent.

There were similar improvements among chronically ill patients who reported getting regular care, with the share in Arkansas jumping from 62 percent to 74 percent and in Kentucky from 69 percent to 79 percent.

By contrast, fewer low-income Texans reported getting a checkup or getting regular care for a chronic condition in 2015, compared with 2013. The authors cautioned that the increased use of recommended care does not guarantee these patients will get healthier in the future.

But Sommers called the findings "encouraging," noting that improved measures of health — such as lower cholesterol or blood pressure — may be a few years off.

Nonetheless, the study's authors say, the results from Arkansas and Kentucky should help inform debate in other states. "Our study suggests that coverage expansion can produce substantial benefits for low-income populations," they concluded.

The researchers surveyed approximately 9,000 low-income adults in Arkansas, Kentucky and Texas.