(Adds CEO comments from conference call, closing share price, details)

By Lynne Olver

TORONTO, July 31 (Reuters) - Profit at Sun Life Financial (SLF.TO: Quote, Profile, Research) fell 12 percent in the second quarter after a slew of unfavorable factors, from stock market performance to credit-related losses, hurt results in the United States, particularly the U.S. annuities business.

The results were worse than analysts had expected, and hammered Sun Life's shares, which fell 6.1 percent on the Toronto Stock Exchange to close at C$39.80 on Thursday.

"Notwithstanding volatile markets, these are disappointing results," Chief Executive Don Stewart said on a conference call.

Sun Life's board felt it was "prudent" to keep the dividend where it was, in light of current economic uncertainty, Stewart added.

"In our view, it's very possible that economic difficulties will intensify over the remainder of 2008 and extend into 2009," Stewart said.

Other executives also remained cautious on the earnings outlook.

"We do not anticipate that macroeconomic conditions will improve in the near term, and credit could be a drag on U.S. earnings for the remainder of 2008," Chief Financial Officer Rick McKenney said on the call.