The trillion-dollar asset manager said in a report in October that BBB-rated bonds, the lowest bracket of the investment-grade debt, now accounts for more than 50% of the market compared to 17% in 2001.
As demand for investment-grade debt has grown, the creditworthiness of issuers has fallen. According to BlackRock, leverage levels are creeping toward the highest readings since 1992. The firm measured leverage using a ratio of debt minus cash and cash equivalents to twelve-month EBITDA.
"We believe the sharp increase in the proportion of BBB-rated constituents has made the investment-grade bond sector riskier than in recent years," BlackRock wrote. "BBB-rated bonds are typically the most vulnerable of all investment-grade debt in a recession."
If BBB-rated bonds are downgraded, they would then be considered high-yield debt, or "fallen angels." That could cause the value of the issues to fall, the firm added.