UnitedHealth (UNH) reported a stronger-than-expected 6% increase in second-quarter profit on better expense management and enrollment among older customers and lifted its full-year earnings and sales forecasts.

UnitedHealth, which is the first major health insurer to report earnings after the U.S. Supreme Court upheld President Barack Obama’s healthcare law last month, boosted its outlook for 2012 revenues to $110 billion, which matches Wall Street views.

The biggest U.S. health insurer lifted its earnings guidance to the range of $4.90 to $5 a share. Analysts on average are looking for at least $4.99 a share.

The benefits manager reported net earnings of $1.34 billion, or $1.27 a share, compared with a year-earlier $1.27 billion, or $1.16. Analysts in a Thomson Reuters poll were expecting just $1.19 a share.

Revenue for the three-month period climbed 8% year-over-year to $27.3 billion, matching the Street’s view. The gain was fueled by a 305,000 increase in new customers during the second quarter, led by retired customers.

Sales in the health benefit provider’s Medicare and retirement group climbed 12% to $10.1 billion with Medicare enrollment growing by 18% as baby boomers continued to retire.  

“We remain focused on balanced growth, ever-improving service and execution, and practical innovation to better engage health care resources to serve more Americans, more affordably,” UnitedHealth CEO Stephen Hemsley said in a statement.

The improved revenues were padded by a 20-point year-over-year decrease in operating cost ratio to 15%. UnitedHealth attributed the decline to faster growth in revenues from services, products and fee-based benefits, as well as investments in the pharmacy-management services business. The insurer’s tax rate was also lower.

Shares of the Minnetonka, Minn.-based company, which is seen as a bellwether for the broader health benefits market, ticked more than 1% higher to $57 on Thursday following the announcement.

Follow Jennifer Booton on Twitter at @Jbooton