U.S. 30-year mortgage rates dropped to a record low in the past week, according to a survey released Thursday by Freddie Mac, as concerns mounted about the economic recovery.

Rates on 30-year fixed-rate mortgages, the most widely used loan, averaged 4.57 percent for the week ended July 8, down from the previous week’s 4.58 percent and 5.20 percent a year earlier, according to the survey, which started in April 1971.

“With mortgage rates falling to historic lows, refinance activity has been strong over the past three months,” Frank Nothaft, Freddie Mac vice president and chief economist, said in a statement.

Freddie Mac is the second-largest U.S. mortgage finance company.

While low rates and high affordability have helped the housing market gain ground, it has struggled in recent months given stubbornly high unemployment and mounting foreclosures.

Freddie Mac said the 15-year fixed-rate mortgage averaged 4.07 percent, up from 4.04 percent last week.

Mortgage rates are linked to yields on Treasuries and yields on mortgage-backed securities.