U.S. health insurance premiums have climbed faster than wages and inflation this year, and look poised to accelerate in 2013.

A study released Tuesday showed that premiums for employer-sponsored health plans, which cover about 149 million Americans, grew a modest 4 percent to $15,745 in 2012. It was a substantially slower rate of growth than in past years, including 2011, when premiums jumped 9 percent.

But the study's authors, at the nonpartisan Kaiser Family Foundation and the Health Research and Educational Trust, said higher costs still took a bigger bite from the income of middle-class employees, whose wages advanced only 1.7 percent, as employers shifted more health care costs to their workers.

This year's 4 percent increase eclipsed a general inflation rate of 2.3 percent. Some employers told researchers that insurers plan to push premiums up another 7 percent in 2013, the study said.

Rising costs could present a challenge for both President Barack Obama and Republican Mitt Romney in their battle for the White House.

They also pose a dilemma for employers, which shoulder most of the cost and face the choice of absorbing ever-higher charges or making their workers pay more.

Polling data show that soaring health care costs rank alongside the government's Medicare program for the elderly as a top campaign issue for voters.

Premiums for employer health plans have doubled over the past decade, with worker contributions surging, on average, to $4,316 from $2,137 in 2002, according to the study's January-to-May survey of 2,100 public- and private-sector employers.

Employer contributions hit an average $11,429 this year, up from $5,866 in 2002.

About 61 percent of companies offer health benefits to their workers. But researchers found that workers at lower-wage companies pay $1,000 a year more for family coverage than workers at higher-wage companies.

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Data also showed a 26-percent jump in the number of young adults receiving health care benefits on parental plans under health care reform, which extends childhood coverage to age 26. There are now 2.9 million young adults on their parents' plans, up from 2.3 million in 2011, the study said.