NEW YORK — The stock market isn’t the only place that’s been signaling jitters among investors. The $2.3 trillion market for risky U.S. corporate debt has also been under pressure.

A five-year rally in junk bonds abruptly stalled last month. As with other higher-risk investments, investors have pulled back mainly because they worry about the end of the Federal Reserve’s policy of near-zero interest rates. Investors expect the central bank to raise rates sometime next year, and that means the value of bonds currently held in portfolios will fall.

Junk, or high-yield, bonds are sold by companies with relatively high debt in comparison to their income. If yields on safer bonds like Treasurys were to climb, they would draw more investor interest. Companies selling junk bonds would then have to increase their yields to compensate investors for the higher risk. Doing so would diminish the value of junk bonds in circulation.

In July, those concerns hit the market, leaving junk bond investors with a 1.3 percent loss for the month. It was the worst monthly performance since June 2013.

Junk-bond yields have fallen so far that many investors now feel the risks outweigh the potential return. Five years ago, the average junk bond yielded 11.5 percent. By June, the yield had dropped to a record low of 4.83 percent, according to data from the investment bank Barclays.

As a result, investment advisers have become less enthusiastic about recommending junk bonds to clients.

There is often some role for high-yield bonds in investors’ portfolios, but “there’s a time to dial it up, and a time to dial it down,” says Darrell Cronk of Wells Fargo Wealth Management. “Now is a time to dial it down.”

Cronk says junk bonds may continue to slump as the economy improves and investors push up Treasury yields in anticipation of the Fed nearing its first interest rate increase since May 2006.

“The risk-reward trade-off is not that attractive anymore,” says Collin Martin of the Schwab Center for Financial Research.

The market for risky bonds has become more mainstream since the 1980s, when trading was dominated by Michael Milken, the junk-bond financier, and his now-defunct firm Drexel Burnham Lambert. In those days, the market made headlines for helping fund takeovers of companies such as RJR Nabisco. Milken’s reign as the king of junk bonds ended in 1989, when he pleaded guilty to securities fraud and defrauding a mutual fund.

Investors plowed $55.01 billion into junk bond mutual funds last year, more than double the $22.1 billion total for 2009, according to data from the Investment Company Institute. Signs now suggest that investors have started pulling back. As the high-yield market started to wobble in June, investors withdrew $4.9 billion, according to the most recent data from ICI.

The recent outflows came as Fed Chair Janet Yellen said that she was concerned that investors were becoming complacent about the risks of investing in high-yield bonds.

Yellen told reporters in June that the market was showing evidence of “reach-for-yield” behavior, when investors focus on return irrespective of risk. One sign of this behavior is the fact that investors have been demanding less of a premium to hold high-yield debt compared to high-quality government debt.

At the start of 2012, investors received a yield premium of 6.99 percent over Treasury notes, which are widely considered to be risk-free. By June, that cushion had fallen to 3.23 percent.

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