Standard & Poor's and Moody's Investors Service are cutting corporate debt ratings at the fastest pace since 2009 as a global economic slowdown and record borrowing erode credit quality.

The ratio of ratings downgrades to upgrades worldwide climbed to 1.85 this year from 1.23 in 2011, according to S&P data. PSA Peugeot Citroen, Europe's second-largest carmaker, was cut three times by Moody's since March to speculative grade. Fort Worth, Texas-based RadioShack Corp. was lowered four steps this year by S&P to seven levels below investment grade. Defaults rose to 80 issuers from 52 in 2011, according to S&P.

Europe's second recession in four years and slowing global economic growth are helping to push a measure of corporate debt to earnings to a three-year high, Barclays Plc data show. Companies from the neediest to the most creditworthy sold unprecedented amounts of debt at record-low yields in 2012 as the Federal Reserve held interest rates at almost zero for a fourth year in an effort to boost the U.S. economy.