Fitch Ratings said Thursday it downgraded its rating on Sterling Bancshares Inc. because of concerns about the Texas bank holding company's exposure to commercial real estate.

Fitch said 62 percent of Sterling's loan portfolio consisted of commercial real estate loans as of Dec. 31, an amount higher than its peers. It downgraded its rating to 'C' from 'B/C' and revised its ratings outlook to negative from stable.

Fitch affirmed Sterling's long- and short-term issuer default ratings at 'BBB'-, the lowest investment-grade rating. The agency said that partly reflects the company's ability to increase capital through its recent offering of $80 million common shares.

Sterling shares declined 16 cents, or 3.2 percent, to $4.77 in afternoon trading.