The leader of UnitedHealth Group, the nation's largest health insurer and Minnesota's largest company, said Tuesday that expanding Medicare to all Americans would destabilize the nation's health care system.

UnitedHealth favors universal coverage through the expansion of existing private and public programs, Chief Executive David Wichmann said. He criticized the prospect of a government-led single-payer system, sometimes called Medicare for All, that would effectively eliminate private health insurers like UnitedHealthcare.

"The wholesale disruption of American health care being discussed … would surely jeopardize the relationship people have with their doctors, destabilize the nation's health system and limit the ability of clinicians to practice medicine at their best," Wichmann said. "And the inherent cost burden would surely have a severe impact on the economy and jobs, all without fundamentally increasing access to care."

In addition to UnitedHealthcare, the Minnetonka-based company operates Optum, which runs clinics, manages pharmacy benefits and offers consulting on health care data.

UnitedHealth Group's shares fell 10% over several days last week after Vermont Sen. Bernie Sanders, a Democratic contender for president, renewed his proposed Medicare-for-All legislation and drew other leading Democrats to support it. President Donald Trump and other Republicans oppose the idea.

Wichmann made the comments to investment analysts as the company announced a 22% jump in profit for the first three months of the year, a performance that easily beat investors' expectations. Executives also raised their outlook for the rest of 2019. Even so, UnitedHealth Group shares on Tuesday tumbled 4% and were at their lowest price in nearly 14 months.

"Investors continue to trim their exposure to political headline risk," Charles Rhyee, an analyst with Cowen Equity Research, wrote in a note to investors.

"We believe the market is ascribing an inordinately high probability that some form of Medicare-for-All proposal could become reality," Rhyee wrote. "Support among centrist Democrats, particularly Democratic leadership, is noticeably absent."

Earlier this month, Sanders and 14 Democrats in the Senate introduced the "Medicare for All Act of 2019" with promises of "eliminating profit-driven health insurance corporations" and instead providing universal coverage though a government program. Such an approach, Sanders said, would address high per-capita costs for a system that leaves many without coverage and others with high medical bills.

Sanders also said the program would maintain doctor choices, lower the cost of prescription drugs and expand benefits covered by health insurance. Rather than pay private insurers to administer the health care system, Sanders said, his proposal would invest those sums in expanded primary care that would, in turn, reduce costly ER and hospital visits.

"Today, the traditional Medicare program only spends 2% of its cost on administration," according to background materials issued by Sanders last week. "That's less than one-sixth the administrative costs of private health insurance companies."

On Tuesday, Wichmann said proposals such as Sanders' contrast with the current system's "real progress," such as the push for digital infrastructure that helps doctors provide more efficient care.

Private health insurers are changing the payment system to promote better patient outcomes, Wichmann said, while encouraging people to take responsibility for behavioral choices that add costs. There's also action to address "social determinants of health," he said, such as the lack of affordable housing.

As of March 31, UnitedHealthcare covered 27.5 million Americans in private plans and 16 million people in Medicare and the state-federal Medicaid program.

"For 16 straight months, health care's relative economic burden on society has lessened," Wichmann said. "While recent year-over-year spending growth at just over 4 percent is still too high, it has lessened considerably due to better management of price inflation and earlier and more effective management of care in lower cost settings."

A Kaiser Family Foundation report in March found a modest increase over time in support for single-payer health care.

"There is robust support among Democrats, and even support among Republicans, for an expansion of the Medicare program through a Medicare buy-in or a Medicaid buy-in proposal," the report found. "Yet, it is unclear how much staying power this support has once people become aware of the details of any plan or hear arguments on either side."

The sell-off in UnitedHealth Group shares hasn't been driven solely by the talk about Medicare-for-All proposals.

Its Optum unit includes a pharmaceutical benefit manager (PBM) business, an industry under scrutiny for its role in the rising cost of prescription drugs.

Congress conducted hearings last week on the industry, and the Trump administration earlier this year proposed eliminating the rebates that PBMs negotiate with drug companies. Critics say those rebates made medicines less affordable as middlemen pocket more and more discounts.

Andrew Witty, chief executive of Optum, repeated to analysts Tuesday the industry's line that PBMs provide one of the few checks on drug prices by aggregating the demand of consumers. "If there is a situation where rebates or a mechanism to replace rebates was not in place, we could see significant drug price inflation over the next years," Witty said.

In the first three months of the year, UnitedHealth said Tuesday, it earned $3.47 billion.

Christopher Snowbeck • 612-673-4744 Twitter: @chrissnowbeck