Aviva Aron-Dine is the vice president for health policy at the Center on Budget and Policy Priorities.Visit Business Insider's homepage for more stories.A landmark new study shows the life-saving benefits of the Affordable Care Act's expansion of Medicaid to more low-income adults, adding to the evidence on the program's importance to low-income Americans.According to the new study by economists Sarah Miller, Sean Altekruse, Norman Johnson, and Laura Wherry, Medicaid expansion saved at least 19,200 lives in the states that expanded. Conversely, 15,600 lives were lost in states that failed to expand Medicaid.The study shows the benefits of Medicaid expansion and gives fuel to the fight to expand the program in states where it meets resistance.The fight to expand Medicaid continuesThe new findings come at an important time. The ACA's Medicaid expansion made adults with incomes below 138% of the poverty line (about $35,500 for a family of four) eligible for the program, opening the door for millions of low-income Americans to get health insurance. Before the ACA, the typical state covered only parents with incomes below about two-thirds of the poverty line, and Medicaid generally did not cover adults without children at all.Expansion has been adopted by 33 states and the District of Columbia, covering 13 million newly eligible people. That includes 13 states that voted for Donald Trump, and every state where voters have weighed in directly through a ballot initiative.The battle to expand the lifesaving program continues in other states. In Missouri and Oklahoma, voters will likely have the opportunity to pass Medicaid expansion at the ballot box in November 2020. And there are debates about expansion in Kansas, North Carolina, Wisconsin, and elsewhere.On the other hand, expansion efforts continue to face fierce opposition. Georgia's governor recently proposed an alternative to expansion under which the state would, by its own estimates, spend as much or more to cover 400,000 fewer people.And at the urging of the Trump administration, some expansion states, such as Arkansas and Idaho, have adopted harmful policies sharply restricting eligibility for their programs, though a number of states are now reconsidering these policies.A huge life-saving benefitIt can be hard to put into context the number of lives saved and lost, so consider two comparisons.First, if all states had expanded Medicaid, the 13,330 lives saved just among older adults in 2017 would roughly equal the total number of total lives saved by seatbelts that year. In other words, expansion's life-saving potential ranks with other major public-health interventions.Second, the aggregate reduction in premature deaths translates into a sizable drop in annual mortality rates for the low-income older adults who gained coverageas much as 64%. That's almost as large as the gap in mortality rates between poor and middle-income older people, strongly suggesting that expanding Medicaid could sharply reduce health disparities.The authors of the study reached these conclusions by putting together a new and very large data set that let them closely examine deaths among low-income people in their 50s and early 60s in expansion and nonexpansion states.They found that mortality trends for low-income older people were about the same across the two groups of states before expansion took effect but then sharply diverged with mortality rates dropping in states where the expansion was adopted. And the authors offer strong evidence that these lives were saved because of expansion.For example, mortality trends didn't improve in Medicaid expansion states for people age 65 and older who were already eligible for Medicare or for people at higher income levels who weren't eligible for Medicaid.And the drop in premature deaths wasn't driven by causes like car accidents, but instead by causes like heart disease and diabetes. Other studies have already shown that expansion leads to a large increase in low-income people getting medications to control diabetes, high blood pressure or cholesterol, and other chronic conditions, as well as improvements in diabetes and hypertension control.This is just one of many recent findings as researchers continue to delve into the experience of expansion versus nonexpansion states. Other studies find Medicaid expansion sharply reduces housing evictions; leads to earlier detection of lung, skin, and breast cancers; and increased the number of people getting medication-assisted treatment, the gold standard treatment for opioid use disorder, by about 50%.To defend their stance, opponents of expansion have often argued that the coverage Medicaid offers isn't high quality.President Trump's Council of Economic Advisers, for example, claimed in 2018 that the jury was still out on whether Medicaid improves health at all. That claim already flew in the face of the evidence, but the latest research should put it to rest once and for all.There is no way to deny that, by refusing to expand, state policymakers are denying lifesaving care to thousands of their residents.Join the conversation about this storyNOW WATCH: A 45-year-long study discovered trends in successful hyper-intelligent children Click here to read full news..