Investors with high hopes for high profits nipped UnitedHealth Group on Thursday after the company said its third-quarter earnings rose only a little.

While the performance was on par with projections, the Minnetonka-based insurance giant declined to raise its profit outlook for the year and offered a somewhat cloudy forecast for its Medicare business in 2014, which helped fuel the slip.

Several analysts dismissed Wall Street's skittish response as nothing more than an attitude adjustment, as the company has consistently outpaced expectations in recent years despite the uncertainty of health care reform.

"Walking into the quarter, the investment community expected them to beat and raise," said David Heupel, senior health care analyst at Thrivent. "We've now probably gotten into a model that's more realistic."

Shares of UnitedHealth ended the day down about 5 percent, at $71.37. Before Thursday, its shares had risen 39 percent this year to be one of the strongest performers in the Dow Jones industrial average.

Analyst Sheryl Skolnick of CRT Capital Research Group said despite investors' response, the quarterly performance was a far cry from being "a disaster." UnitedHealth slightly missed her revenue estimate but beat her profit forecast. "For our part, we see this as an extremely strong report with no fundamental problems in the business," she said.

Profits rose less than 1 percent to $1.57 billion, or $1.53 per share, compared to $1.56 billion a year ago. That matched the average of 18 analysts' estimates polled by Bloomberg.

Enrollment grew 24 percent from a year ago to 45.3 million people, which helped boost revenue by 12 percent to $30.62 billion. Analysts had predicted revenue to be higher at around $30.9 billion.

UnitedHealth is the first of the national insurance companies to release earnings and is seen as an indicator of how the sector is performing as the federal health law rolls out.

It has already adjusted to some of the early challenges of the law, known also as Obamacare, including a provision that forces all insurers to spend at least 80 cents on every dollar on direct medical spending. UnitedHealth is participating in about a dozen state-run public exchanges that launched Oct. 1, preferring to take a go-slow approach until the markets and premium pricing level out.

But CEO Stephen Hemsley signaled more headwinds ahead.

The company has seen rising enrollment in recent years mainly through government-backed programs of Medicare, which covers seniors and those with disabilities, and Medicaid, which covers low-income citizens. But swelling membership in its Medicare Advantage plans came as the government cut reimbursements, which cut into profits. The pressure on its insurance business is neither new nor unexpected, Hemsley said. "The significant and continued level of underfunding cannot be fully offset in 2014 from the positive performance we expect from the balance of our health benefits markets," he said.

For the year, the company projected earnings at $5.40 to $5.50 per share, raising the lower end from the $5.35 projection given in July.

"This result may disappoint investors looking for a larger beat and more of a raise this year given the continued low utilization environment," Thomas Carroll, analyst at Stifel Financial Corp., wrote in a research note. Carroll added that he believes "the case for continued outperformance exceeds that of disappointment — but just barely."

UnitedHealth's medical services division, Optum, is outpacing the company's expectations. It now contributes 30 percent of overall income, ahead of what Hemsley said was a "15 by 15" pace. Profit at Optum grew 54 percent during the quarter and now comprises about a quarter of operating earnings.

Thrivent's Heupel said Optum continues to provide a strong counterbalance to the highly regulated and volatile insurance side of the firm, something that sets it apart from its competitors. "Optum is on fire, continuing to outperform on the top and bottom line," he said.