The first full year of the Affordable Care Act brought historic increases in coverage for low-wage workers and others who have long been left out of the health care system, a New York Times analysis has found. Immigrants of all backgrounds — including more than a million legal residents who are not citizens — had the sharpest rise in coverage rates.

Hispanics, a coveted group of voters this election year, accounted for nearly a third of the increase in adults with insurance. That wasthe single largest share of any racial or ethnic group, far greater than their 17 percent share of the population. Low-wage workers, who did not have enough clout in the labor market to demand insurance, saw sharp increases. Coverage rates jumped for cooks, dishwashers, waiters, as well as for hairdressers and cashiers. Minorities, who disproportionately worked in low-wage jobs, had largegains.

The health care law was one of the most bitterly contested pieces of legislation in the country’s history. It remains controversial because of its costs to both taxpayers and insurance customers. The high premiums and high deductibles of many plans still make coverage a crushing financial burden for some families.

And the law is not close to achieving the goal of universal coverage, in part because 19 states have declined to expand their Medicaid programs for the poor, an option the Supreme Court granted them in a landmark 2012 case. Nevertheless, the Times’s analysis shows that by the end of that first full year, 2014, so many low-income people gained coverage that it halted the decades-long expansion of the gap between the haves and the have-nots in the American health insurance system, a striking change at a time when disparities between rich and poor are growing in many areas.

«The law has clearly reduced broad measures of inequality,» said David Cutler, an economics professor at Harvard, who served in theClinton administration and advised the 2008 Obama campaign on health issues. «These are people who blend into the background ofthe economy. They are cleaning your hotel room, making your sandwich. The law has helped this population enormously.»

Until now, the impact of the law has been measured mostly in broad numbers of newly insured people — about 20 million by theadministration’s most recent account . But the Times’s analysis of census data from 2014, the first year the heart of the law was in full effect, provides a finely detailed look at who the newly insured actually are — by race, education, occupation, immigration status, and family structure.

The analysis shows how the law lifted some of the most vulnerable citizens. Part-time workers gained insurance at a higher rate than full-time workers, and people with high school degrees gained it at double the rate of college graduates. Adults living in households headed by relatives, such as siblings or cousins — often a marker of economic distress — gained insurance at double the rate of those in traditional households.

The law’s passage, without a single Republican vote, capped decades of efforts to enact a broader health insurance system. Medicaid and Medicare passed in the 1960s, but did little to help workers who did not receive insurance through their jobs. Presidents Nixon, Carter and Clinton all tried and failed to win approval for expanded coverage, and the number of uninsured Americans grew to nearly a fifth of adults under the age of 65 by 2010 , the year the Affordable Care Act passed.

The findings from the census data could inform the national dialogue, especially in this election year. Hispanics are a powerful voting force and the law is viewed favorably in Hispanic neighborhoods. But whether the sharp increase in coverage rates for Hispanics will translate into votes for Democrats who supported the law, or whether some Republicans might temper their vows to repeal it, is not clear. And the fact that so many who benefited under the law were not citizens (or voters) — 1.2 million out of the total 8.7 million who got health insurance in 2014 — could set off a new round of debate in a year when immigration has become a deeply polarizing issue.

About 60 percent of those noncitizens were Hispanic, mostly natives of Mexico and Central America who had been living in the United States for decades. Another third were Asian, mostly newer arrivals living in states like California, New York and Texas. Illegalimmigrants are not eligible for insurance under the law, but legal immigrants who have been in the country for more than five years are.

The vast majority of the country’s 11 million illegal immigrants, about 70 percent of whom are Hispanic, still lack coverage, said Mark Hugo Lopez, director of Hispanic research at the Pew Research Center.

Though the law has withstood two Supreme Court rulings that would have undermined its central elements, it continues to face challenges.

It requires most Americans to have health insurance and gives subsidies to those who cannot afford it. Even so, many still cannot afford policies. While it expanded Medicaid to cover more of the country’s poor, the Supreme Court allowed states to opt out and 19 have , leaving millions of people still uncovered.

But in low-income neighborhoods like this one in South Los Angeles, a historically poor patch of the city dotted with palm trees, small ranch houses and home to a growing Hispanic population, the law is having a big effect.

«From the vantage point of the poor and working poor, Obamacare has been profound,» said Jim Mangia, president of the St. John’s Well Child and Family Center, a federally funded health clinic in South Los Angeles that has enrolled 18,000 new patients under thelaw, nearly all of them Hispanic or black and the vast majority in Medicaid. The clinic reported a 44 percent increase in cervical cancer screenings, a 25 percent increase in tobacco cessation therapy, and a 22 percent increase in the share of patients with controlled hypertension since 2014, the result, he said, of more patients having insurance.

One new patient, Angela Cruz, 60, is a typical example of a winner under the law. A legal immigrant who is not a citizen, she came to this country from El Salvador in 1990. She had never had health insurance in her 25 years of working in the United States, most recently as a nanny. She stitched together medical care through emergency rooms, free clinics and home remedies. When she needed to pay for medicine for a painful bout of kidney stones , she stopped buying meat.

Then she got coverage under the health law’s expansion of Medicaid in California.

Now, she said, «I don’t have the stress of wondering — can I pay this — when sometimes I didn’t have anything to pay it with.»

Hispanics remain the least insured Americans, with only 67 percent having coverage in 2014, in part because so many illegalimmigrants are uninsured.

Gains for blacks were muted because they disproportionately live in states that chose not to expand Medicaid. About 60 percent ofpoor blacks live in states that did not expand Medicaid. While the share of poor blacks covered by Medicaid did rise by two percentage points in those states, the rate rose by six points in states that expanded the program.

In all, minorities gained more than whites, making up two-thirds of the increase in insured adults across the country, and 70 percent of the increase in private insurance. Minority men who work as groundskeepers and janitors saw substantial gains, rising to 59 percent insured, up from 51 percent in 2013. Hispanic male construction workers rose to 43 percent insured, from 36 percent in 2013.

One such worker, Sergio Ortega, 51, a legal immigrant from Mexico who had never been insured before getting covered by Medicaid in 2014, said making a doctor’s appointment seemed unthinkable without insurance, so he often simply ignored his health problems.

Several years ago, he started feeling tired, a condition that eventually drove him to quit his job demolishing buildings and start selling fruit from a street cart. By the time he sought treatment through his new coverage and discovered he had diabetes , his lower leg had to be amputated.

«I realized it was getting really bad because my foot started turning purple,» said Mr. Ortega, who is a patient at St. John’s.

Perhaps the biggest unmet promise of the law is that many it was supposed to help still cannot afford insurance. Alberto Torres, 50, a driver for a garment company in Los Angeles who could not afford insurance before the law, had signed up for a plan in 2014 for $41 a month. But this year his monthly premium jumped to $106 — too much, he said, for his meager salary.

«I’m feeling not so good,» he said recently, waiting in line for help to look for a less expensive plan.

High deductibles are another big obstacle. «If you are living paycheck to paycheck and have nothing in the bank, insurance with a $3,000 deductible might feel like no insurance at all ,» said Larry Levitt, a senior vice president of the Kaiser Family Foundation.

Having insurance does not necessarily mean better health, but experts hope it could start to ease some of the worst disparities that have kept the United States close to the bottom of health rankings of rich countries.

Mr. Ortega has been fitted for a prosthetic leg. He is still learning how to use it.

«Now I don’t worry,» he said. «It’s a security, a comfort that I feel.»

Immigrants, the Poor and Minorities Gain Sharply Under Health Act