Unum Group reported an increase of 19 percent in operating income for the first quarter, although net income was down due to an accounting charge on investment losses.

The company, which is headquartered in Chattanooga, Tenn., and has about 3,500 employees in Portland, said operating income for the quarter was $207.8 million, or 59 cents a share, compared to $174.6 million, or 50 cents a share, during the same period a year ago.

Net income, including the charge related to changes in the value of derivatives, was $163.1 million, or 46 cents a share, for the three months ending March 31, compared with 2007 results of $178.3 million, or 51 cents a share.

Unum also said it is increasing its earnings guidance to $2.37 and $2.42 a share for 2008, based in part on a continued improvement in benefit ratios.