That health-care costs in the country are expensive—often, prohibitively so—is well known. As Vox’s Sarah Kliff notes, the first reason why is the exorbitantly high cost of care, which doesn’t always correspond with measurable increases in quality or demand. Even for routine procedures or precautionary visits, hospital bills can run over $400, an expense that almost half of American households can’t meet without dipping into credit. Additionally, billing is famously opaque, incoherent, and fragmented, creating major barriers to informed care decisions and often resulting in bills going into collections.

Health insurance is supposed to mitigate those cost and information barriers. A 2016 Kaiser Family Foundation analysis found that while significant numbers of Americans have trouble paying medical bills, only 20 percent of insured people had difficulty versus half of all uninsured people. Most of that difficulty for both groups comes from sudden medical events or accidents, or sudden life events like the loss of a job. Medical debt is also a major contributor to bankruptcy in the United States. One of the major arguments for the Affordable Care Act was in its name: a promise to help shield people from the worst financial effects of medical catastrophe or chronic illness.

New avenues of subsidized or free health insurance that sprang from Obamacare—including private insurance offered on the exchanges and expanded Medicaid rolls in many states—have been able to do some shielding. The ACA helped reduce total bankruptcies by as many as 1.5 million between 2010 and 2017. The Centers for Disease Control and Prevention reports that, between 2011 and 2016, the percentage of Americans with trouble paying medical bills dropped precipitously. And a 2017 study by the Urban Institute’s Kyle Caswell and Timothy Waidmann found “improved credit scores, reduced balances past due as a percent of total debt, reduced probability of a medical collection balance of $1,000 or more, … and a reduction in the probability of a new bankruptcy filing” for people in Medicaid-expansion states.

But the new AJPH study complicates some of that rosy analysis. The researchers didn’t split the survey population up based on insurance status; they instead measured income inequality across the population, both before medical expenses were taken into account and after. They found that income inequality in 2014 actually increased by 1.5 points after medical expenses were subtracted from income. Put another way, poor people spent much more of their income on health care than the richest people did, and as a result around 1.5 percent of all relative income shifted toward the higher earners.

The researchers also found that medical spending sent millions of people effectively into poverty or into deeper rungs of poverty. Seven million Americans making more than 150 percent of the federal poverty line—$31,000 for a family of three—dropped below that line if medical expenses were subtracted from their income. That meant that these families spent something like a third or more of all their income on health care. Of the 7 million, 4 million found their post-health-care income reduced below 50 percent of the poverty line, meaning they spent about two-thirds of their total income on health care. The study also found that the ACA decreased the amount of inequality caused by health-care expenses, but only slightly.