An article in the WSJ reports that stocks are supported by record levels of borrowing (known as margin debt). Per the author, margin lending growth has proven to be a decent indicator of overvalued markets.
“Rising margin lending from Swiss and U.S. wealth managers can make a downturn far more painful. … In the U.S., margin debt is more than three-times the level ahead of the 2008 crisis and is greater even than its peak in 2000 before the dot-com crash, according to the B.I.S.”