The American consumer’s long-running love affair with debt appears to be on the rocks. But like a lot of soured romances, the reasons are open to debate.

What’s known is that the debt held by U.S. households shrank in the three months ended Sept. 30. That’s the first time that has happened since the government began keeping records more than 50 years ago, the Federal Reserve said Thursday.

Economists say consumers appear to be curbing their spending and displaying a healthy prudence about taking on new debt — something financial planners have been admonishing Americans to do for decades.

What economists don’t know is whether people are bringing down their debt voluntarily or whether it’s being imposed on them through foreclosures or the denial of credit.

Household debt declined 0.8% in the third quarter, mostly as a result of a 2.4% decline in mortgage debt, the Fed reported. Other consumer debt, which includes credit card debt, rose a modest 1.2%.

The Fed also noted that household net worth continued to decline in the same quarter, largely because of shrinking home equity. Homeowners’ equity as a percentage of the value of their homes has fallen to just 44.7%. Until this year, that percentage had not fallen below 50% since 1945.