Nancy Beigel, 55, of Beltsville, Md., will be getting health insurance for the first time in about a decade. (Katherine Frey/The Washington Post)

Adam Peterson’s life is about to change. For the first time in years, he is planning to do things he could not have imagined. He intends to have surgery to remove his gallbladder, an operation he needs to avoid another trip to the emergency room. And he’s looking forward to running a marathon in mid-January along the California coast without constant anxiety about what might happen if he gets injured.

These plans are possible, says Peterson, who turned 50 this year and co-manages a financial services firm in Champaign, Ill., because of a piece of plastic the size of a credit card that arrived in the mail the other day: a health insurance card.

Peterson is among the millions of uninsured Americans who are benefiting from the Affordable Care Act, the 2010 law that launched far-reaching changes to the U.S. health-care system and is President Obama’s premier domestic achievement.

These beneficiaries have not been oblivious to the problems of the new insurance exchanges, including a rollout so botched that Obama called it his biggest mistake of the year. Many, including Peterson, had firsthand encounters with the error-prone federal Web site,, that tested their patience and resolve. Some called help lines that couldn’t help them. Others drove long distances to meet with trained enrollment workers who couldn’t get them enrolled. Yet they persisted.

And as New Year’s Day approaches, and with it, health insurance, their frustration is trumped by gratitude. “I get these messages from acquaintances on Facebook saying, ‘Let me keep my doctor,’ ’’ Peterson said. “Well, what about those of us who didn’t have health insurance before? . . . I have been walking a tightrope and have had some twists and falls off of it. To not have to worry about this anymore is a tremendous relief.”

Getting Americans health insurance is at the heart of the health law, the most significant change in health-care policy since the 1965 creation of Medicare, the federal program for the elderly, and Medicaid, the federal-state program for the poor and disabled. Such a dramatic expansion in coverage had eluded presidents, including Republican Richard Nixon and Democrat Bill Clinton, for decades.

This core mission has sometimes been obscured by the political and legal disputes that have dogged and, in important ways, altered the law. Strong research links having health insurance and being healthy. Having a health plan does not guarantee that a good doctor is within reach when a patient needs one. But insurance matters.

Dan Munstock knows this. A 62-year-old retiree in Greenville, Tenn., he hasn’t had insurance since he left his job as a crisis counselor in Miami six years ago. He lives on Social Security income of less than $15,000 a year. Although he does not know of any major ailments, he would like a checkup because, he said, “you can seem fine until the day you drop over with something.”

Like thousands of other Americans, Munstock ran into technical problems with the federal Web site before managing to pick a health plan Dec. 1. He qualified for a federal subsidy to help him afford the insurance, so he has to pay just $87.57 a month toward his premium. After his welcome packet from Blue Cross Blue Shield of Tennessee arrived in the mail, Munstock was so eager to finish the process of enrolling and getting an insurance card that he picked up the phone to pay the first premium instead of using the mail.

“It felt really good,” he said. Paying toward his own insurance, he said, gives him “a certain dignity,” a feeling that he is not “one of the takers.” The next day, he called the doctor’s office. His appointment for a physical is Jan. 2.

“I’m feeling surprisingly moved by all of this,” Munstock said. “This finally seems real. And I’m thinking that maybe all the talk and the promises and the messy politics can actually lead to something good after all.”

‘Desperate’ for insurance

Various studies have found that children without insurance are less likely to get immunized or treated for a sore throat or even a ruptured appendix. Adults without coverage are less likely to get mammograms or prostate exams. If they have high blood pressure or diabetes, it is more likely to be out of control. If they have a stroke, it is more likely to leave lasting damage. The Institute of Medicine has said there’s “a chasm” between the health needs of uninsured people and their access to effective care — a gap that “results in needless illness, suffering and even death.”

In health-care economics, it is considered rational to provide coverage, so that people can readily get small medical problems taken care of before they become big, expensive, pent-up medical problems. But the gallbladder surgery Peterson is about to have and the unforeseen ailments that Munstock’s physical on Thursday could unearth also illustrate a risk for the health plans that have been signing up new patients under the law: Unless those plans also attract new customers who are young, healthy and inexpensive to insure, the rush of people like Peterson and Munstock is going to freight the new system with costs that are too heavy. Insurance rates could go up. Plans could drop out. Will it happen? No one knows.

That is the macro view. The micro view, for people who have been waiting for insurance for years, is financial protection. Hospitals frequently charge uninsured people two to four times what health insurers and government programs pay for hospital services, according to a 2007 Health Affairs study.

In the years since Medicare and Medicaid were created, there have been smaller expansions in government health-care coverage — public insurance for children of the working class, the addition of drug benefits to Medicare.

Still, nearly 48 million Americans were uninsured as of 2012, according to the most recent official figures — 11 million more than at the turn of the century, or almost one in every six people. More than 6.5 million children are uninsured.

The law wasn’t designed to help everyone who is uninsured. But it is likely to cover a big chunk — 32 million people, according to estimates from the Congressional Budget Office about the time Obama signed the 2,000-page legislation into law.

How many people will take up the offer remains to be seen. The CBO has estimated that 7 million will sign up for private plans by the end of the first annual open enrollment period on March 31, while another 9 million will enroll in an expanded Medicaid program or in the Children’s Health Insurance Program.

But with insurers canceling health plans that fail to meet new benefit standards for millions of individuals, and many Americans finding it difficult this past fall to use, it will be hard to know if the ranks of the uninsured will go up or down right away, health experts say. Starting next year, the law requires that most Americans have health insurance or risk a fine.

The creators of the law envisioned that about half the people who gain insurance would enroll in private health plans, the other half in Medicaid. The Supreme Court sliced into the second goal, ruling that states could opt out of the expansion, something that has occurred in many states led by Republicans.

Maryland expanded Medicaid, which means that 55-year-old Nancy Beigel of Beltsville will be getting insurance for the first time in about a decade. With an income of $11,000 a year from her small cleaning service, she hasn’t been able to afford insurance but didn’t qualify until now for Medicaid.

An emergency appendectomy in 2009 ended up requiring two operations — the first one failed to properly remove the appendix. Beigel was left not only with $91,000 in medical debt but also a lump in her abdomen that she believes is a hernia. She hasn’t been to a doctor to get a diagnosis and, in the meantime, she avoids “really heavy lifting” because she’s worried that doing so could cause a potentially fatal complication.

Medicaid, she said, “is not exactly glamorous.” But she is glad to have coverage beginning in January. “I’m so desperate to have insurance,” she said. “For me, it’s fabulous.”

Amy Torregrossa is 27, lives in San Francisco and creates Web tools for political candidates. She has been without insurance only since July, when coverage through her boyfriend’s company ended because he changed jobs. In the months since then, Torregrossa has found that “it’s really scary to not be covered.” She has a congenital heart defect and a history of high blood pressure. She no longer runs, she said, because “if I twist my ankle or get hit by a car . . . any doctor visit is so expensive.”

When California’s insurance exchange opened Oct. 1, she was among the first to sign up, picking a $310 silver plan. She made sure her cardiologist was in the insurer’s network and plans to schedule a checkup for early next year.

As Torregrossa has been worrying about her heart, Emily Wright has been worrying about the mole on her back. The suspicious mole is on a mental list of “little things” that Wright, 28, of Johnson City, Tenn., said she wants to get checked out. Recurring joint pain in a foot and knee are also on the list. So are her frequently swollen glands.

Wright also needs surgery for endometriosis, a painful gynecological condition that has already required her to have two operations. Constant pain makes it difficult for her to work delivering pizzas and attend East Tennessee State University, where she hopes to get a history degree in May.

Enrolling through the federal exchange, she qualified for a federal subsidy and picked a top-tier plan that will cost her $125 a month. The soonest appointment she could get with an obstetrics-gynecology practice, the first step before surgery, is Jan. 17.

“I am excited. I am ready,” she said. “It feels like the light at the end of the long dark tunnel.”

‘A normal life’

For Adam Peterson, awaiting gallbladder surgery in Illinois, the dark tunnel without insurance began about six years ago, when he decided to forgo health coverage because he needed the cash to set up his financial services business. The cost of that decision hit home in March, when the emergency surgery to remove a gallstone cost him $27,000.

When he went to this fall, the online system at first balked at verifying his identity — an essential step. It took a few calls to a help line before anyone called back. But just before Thanksgiving, he managed to enroll in a top-tier plan with a monthly premium of $475.

“I do not feel that it gives me the freedom to do reckless things,” Peterson said, contemplating his insurance coverage, which begins on New Year’s Day. “More, it just allows me to live a normal life with one less worry.”