KHN and NPR embarked on a project to understand how widespread medical debt is in America. Here are the most important takeaways of that yearlong investigation:

• The problem is large. Very large. More than 100 million people, including 41% of adults, are saddled with debt from medical or dental bills, according to a KFF poll conducted for the project. Much of that debt is hidden on credit card balances, in payment plans to hospitals and other medical providers, and through loans patients take out from friends and family. Hospitals, some of them nonprofit or public university systems, often fuel the problem, shuttling patients into loans or selling debt to collection companies.
• The debt is upending millions of lives. About half of adults with health care debt say they have had to make difficult sacrifices. The most common is cutting spending on food, clothing, and other basic household items. But millions of Americans are also taking on extra work, draining retirement accounts, moving out of their homes, or delaying education for themselves or their children. The debt is deepening racial disparities and preventing patients from getting care.
• Health care debt is hard to pay off. One in 8 people with health care debt owe $10,000 or more, the KFF poll found. And although most people with debt expect to repay it, 18% say they don’t believe they’ll ever pay it all off.
• Debt and illness are linked. Debt is more common among low-income and uninsured Americans, but the strongest predictor of whether a community will have high medical debt is how sick its residents are. That’s according to the Urban Institute, which analyzed county-level debt data for this project: In the 100 U.S. counties with the highest levels of chronic disease, nearly a quarter of adults have medical debt on their credit records, compared with fewer than 1 in 10 in the healthiest counties.
• Patient debt is pervasive for a reason. The KHN-NPR investigation finds that despite more people having health insurance — as a result of the Affordable Care Act — medical debt is pervasive. There is a reason: Over the past two decades, health insurers have shifted costs onto patients through higher deductibles at the same time that the medical industry has steadily raised the prices of drugs, procedures, and treatments. The 2010 health care law didn’t curb that.