Fitch Ratings downgraded disability insurance provider Aflac Inc. one notch Monday and took the insurer off its Negative Watch.

The ratings service downgraded Fitch's IDR to A from A+. Both are investment-grade ratings. Fitch also downgraded several of Aflac's outstanding notes to A- from A.

The change "reflects Fitch's belief that Aflac's current profile has weakened given its increased leverage, overall financial sector investment concentration, and large single-name, financial securities," the ratings service said in a statement.

Fitch pointed to $1.1 billion in asset impairments and other losses that have not yet shown up in Aflac's financial statements.

Fitch set the Rating Outlook to "Negative." Such an outlook reflects the possibility for further downgrade if Fitch's investments fall in value enough to cut deeply into Aflac's earnings.

However, Fitch said it believes Aflac will generate strong earnings in 2010, and that the insurer has enough resources to weather some losses.

It affirmed ratings for Aflac subsidiaries American Family Life Assurance Co. of Columbus, American Family Life Assurance Co. of New York and Aflac Japan.