Tristan Berger, 47, who was born with spina bifida, has had 16 reconstructive operations on his feet since age 13. A decade ago, he found himself too disabled to continue working, after a series of falls. His wife has health insurance through her job at Walmart, and he has some income from the Social Security disability program, but nearly all of it goes to his medical bills.

Mr. Berger, who lives in Tucson, said he spent $12,000 last year on care not covered by his health insurance. When we spoke recently, he had already spent a similar amount this year, after his latest orthopedic operation.

“You sit there every month trying to figure out what bill to pay: Do you pay the hospital bill or do you pay the utility bill?” he said. “There’s no savings. We’re part of that percentage of America that are one paycheck from being destitute.”

Sarah Miller, an assistant professor at the University of Michigan Ross School of Business, has studied how health insurance protects Americans from financial risk. The evidence is strong that coverage, particularly Medicaid, makes a difference. But she said it could still prove insufficient for people with complex needs.

“You’re kind of at a disadvantage as a consumer going against these big complicated systems that don’t always have your best interest at heart,” she said. “And I think that’s why there’s so much financial burden, even among people with private insurance.”

Health insurance, of course, provides little help for people who have to cut back on work because of their own illness or that of a family member. Mr. Berger had a steady income and good benefits when he worked as the housekeeping director for a retirement community. But once he became too ill to keep working, his income fell. Fifty-three percent of people in the survey said their work had been interrupted by illness, causing financial difficulties and compounding the burden of medical bills.

Research suggests that such work interruptions can have long-term consequences for people who become ill or are injured. A recent paper in the American Economic Review found that, for middle-aged Americans, going to the hospital could mean an average income reduction of 20 percent that persists for six years or more.