The market for loans to below-investment grade companies is off to its slowest start in five years as regulators step up efforts to curb risky underwriting and investors put their money elsewhere.

About $63 billion of leveraged loans have been sold to money managers this year, down 69 percent from 2014 and the least since $53 billion was issued during the same period in 2010, according to data compiled by Bloomberg. Investors have pulled a net $5.5 billion this year from funds that buy the debt, adding to last year's record $23.9 billion in withdrawals and further denting demand for debt that's backing acquisitions of companies from PetSmart Inc. to Office Depot Inc.

The loan market is mired in a slump that started a year ago as regulators led by the Federal Reserve increased scrutiny on what they deemed excessive risk-taking by Wall Street's biggest lenders. That's prompted some banks to shun deals that don't meet the Fed's underwriting guidelines, at the same time that fund outflows have helped push up borrowing costs, slowing refinancing activity.