DETROIT — Poor people in Michigan with asthma and diabetes were admitted to the hospital less often after they joined Medicaid under the Affordable Care Act.
More than 25,000 Ohio smokers got help through the state's Medicaid expansion that led them to quit.
And around the country, patients with advanced kidney disease who went on dialysis were more likely to be alive a year later if they lived in a Medicaid-expansion state.
Such findings are part of an emerging mosaic of evidence that, nearly a decade after it became one of the most polarizing health care laws in U.S. history, the ACA is making some Americans healthier — and less likely to die.
The evidence is accumulating just as the ACA's future is, once again, in doubt. The most immediate threat arises from a federal lawsuit, brought by a group of Republican state attorneys general, that challenges the law's constitutionality. A trial court judge in Texas ruled late last year that the entire law is invalid, and an opinion on the case is expected at any time from the U.S. Court of Appeals for the 5th Circuit. The case could well put the ACA before the Supreme Court for a third time.
President Donald Trump has dismantled as much of the law as his administration can, by expanding the availability of skimpy, inexpensive health plans that skirt ACA rules, for example, and slashing federal aid to help people sign up for coverage through ACA insurance marketplaces.
And some 2020 Democratic presidential candidates contend that the country needs further-reaching health reforms than the ACA, calling for a government-financed system they call Medicare for All.
When the sprawling 2010 law was new, a central question was whether it would help more people gain affordable health coverage, as intended.
With about 20 million Americans now covered through private health plans under the ACA's insurance marketplaces or Medicaid expansions, researchers have been focusing on a question that was not an explicit goal of the law: whether anyone is healthier as a result.
It is difficult to prove that the law has made a difference in people's health, but some strong evidence has emerged in the past few years. Compared with similar people who have stable coverage through their jobs, previously uninsured people who bought ACA health plans with federal subsidies had a big jump in detection of high blood pressure and in the number of prescriptions they had filled, according to a 2018 study in the journal Health Affairs.
And after the law allowed young adults to stay longer on their parents' insurance policies, fewer 19to 25-year-olds with asthma failed to see a doctor because it cost too much, according to an analysis of survey results published earlier this year by researchers at the U.S. Centers for Disease Control and Prevention.
Most of the emerging evidence concentrates on the health effects of joining Medicaid under the law's expansion of the safety-net program. Medicaid is an appealing research focus because a 2012 Supreme Court decision gave each state the option to widen eligibility to people who are somewhat less poor, allowing comparisons between the three dozen states that have expanded and the rest that have not. In addition, low-income people without insurance are most likely to have built-up medical problems that get treated once they get covered.
Michigan has emerged as a hub for understanding the ACA's effects on health because University of Michigan researchers have been rigorously evaluating the Healthy Michigan Plan, as the state calls its Medicaid expansion covering about 650,000 people.
One 2017 study compared heart surgery patients in Michigan and Virginia, which had not yet expanded Medicaid at the time. It found that those who had cardiac bypasses or valve operations in Michigan had fewer complications afterward than similar people in Virginia, where more were uninsured.
One in three Michigan women said that, after joining Medicaid, they could more easily get birth control. And four in 10 people in Healthy Michigan with a chronic health condition — such as high blood pressure, a mood disorder or chronic lung disease — learned of it only after getting the coverage, according to survey results published this month.
Understanding the ways the ACA has affected Americans' health is a work in progress. In the law's first years, results were mixed, but signs of improvements have accelerated lately, as people uninsured before now have more years of coverage, giving researchers better data to study.
It is too soon to know whether the patterns might reverse with new U.S. Census Bureau data showing that the uninsured rate rose significantly last year for the first time since the ACA took effect.
The findings that exist are not perfect.
One National Bureau of Economic Research paper in July, looking at deaths from all causes among adults from their mid-50s to mid-60s, found that dying in a given year has been significantly less common in the states that expanded Medicaid. The paper said that perhaps 15,600 deaths could have been avoided if the expansion had been nationwide, though the paper said that is a rough estimate.
Similarly, a study last year found that infant deaths — especially among African American babies — were dropping more rapidly in parts of the county that had expanded Medicaid. But the study did not distinguish families who got coverage through the ACA expansions.
The University of Michigan work, including on trends in hospital stays for four main chronic diseases, was able to focus specifically on people who had joined Healthy Michigan. It found that from the first year in the program to the second, hospital stays for asthma plummeted by half and also fell for diabetes complications. But hospital stays for heart failure became more common.
The researchers have not yet looked at the patterns for additional years.
Still, John Ayanian, director of the University of Michigan's Institute for Healthcare Policy and Innovation, said, "the weight of evidence is on the positive side."