UnitedHealthcare's program to invest in affordable housing projects has surpassed the $400 million mark, the health insurer said Tuesday, as projects newly announced this year put the company's multiyear effort on track to create more than 4,500 homes across 18 states.

The Minnetonka-based company is part of a national trend where insurers and health care providers are trying to address the lack of affordable housing and other "social determinants of health" in hopes of helping control medical costs.

Most of UnitedHealthcare's investments have come by way of low income housing tax credit programs, where banks, insurers and other large investors see tax benefits that generate what housing advocates call a "modest" financial return.

In a few cases, UnitedHealthcare has more directly financed projects that provide housing for people who previously were homeless, and now require fewer trips to the hospital or emergency room.

"I think everyone in health care is realizing that housing is health care," said Dr. Jeffrey Brenner, a senior vice president with UnitedHealthcare. "When patients are faced with a whole set of social challenges, and behavior health and addiction challenges, their medical issues can't improve."

UnitedHealthcare, which is the nation's largest health insurer, is a division of UnitedHealth Group, the state's largest company.

Last year, California-based Kaiser Permanente, which sells health insurance while running hospitals and clinics, rolled out a $200 million program to address housing stability, homelessness and other community issues. Indiana-based Anthem, which is the nation's second-largest health insurer behind United, said it has committed more than $380 million to develop affordable housing over the past decade.

Blue Cross and Blue Shield of Minnesota, HealthPartners and UCare said they are supporting smaller projects to help homeless people and promote affordable housing.

"More health care groups, whether they are providers or health insurance organizations, are taking a very keen interest in housing — affordable housing in particular — because housing is, in many cases, the key to improving the health outcomes and reducing health care costs," said Warren Hanson, president of the Greater Minnesota Housing Fund, a nonprofit that has worked with UnitedHealthcare on affordable housing projects in Minnesota.

The UnitedHealthcare initiative began in 2011. This year, the effort has expanded to include four new projects including a $12 million investment in Los Angeles that was commemorated Tuesday with a ribbon-cutting ceremony.

The insurer said it has now invested in 80 affordable housing communities across the country.

United is one of the nation's largest managed care organizations for people in the state-federal Medicaid program, which provides coverage to many groups including those in poverty. The company said its Medicaid data show that when people who are homeless get into stable housing, they can better manage their health.

During an investor conference in 2017, Brenner told the story of a UnitedHealthcare enrollee in Phoenix called T.J., who was homeless and unemployed.

As UnitedHealthcare workers grew to know T.J., they learned that since 2015 he had made 254 trips to the emergency room and had 32 hospital admissions, accumulating more than $294,000 in health care costs.

Four months after UnitedHealthcare connected him with housing, T.J.'s health was improving, he was staying out of the emergency room and starting to set goals, Brenner told investors.

During an interview last year, Brenner said T.J. was still doing well and staying off the streets.

On Tuesday, Brenner described a $22 million loan that United made a few years ago for an affordable housing project in Phoenix that renovated a 400-unit apartment building. The development includes 100 units reserved for people in the insurer's Medicaid HMO, and much of the housing has gone to people who previously were homeless.

"In Phoenix, our homeless members use the emergency room nine times more than the average," Brenner said. "We're seeing something between a 10 and 20 percent reduction in inpatient and ER utilization from the program."

Brenner cited research that looks at the ratio of health care spending to social service spending in different countries. The U.S. is an outlier in terms of spending a disproportionately large amount on health care, he said, and a relatively small amount on social services.

"If you overspend on one part of the system, and underspend on another part of the system, you'll end up medicalizing social problems," Brenner said. "Hospital beds have become the most expensive homeless shelter in the country."

Twitter: @chrissnowbeck