Excess global debt is a major concern for J.P. Morgan's international chairman.
Speaking at the World Economic Forum in Davos, Jacob Frenkel said: "My main concern is problems arise, always, when you are overly optimistic (and) when you take too much debt."
"This was the main lessons from all the previous crises," he added.
The International Monetary Fund (IMF) upwardly revised its global growth forecasts for 2018 and 2019 on Monday, saying the revision is partly down to the recently approved overhaul of the U.S. tax system under President Donald Trump.
Global growth forecasts for 2018 and 2019 have both been revised upward by 0.2 percentage points to 3.9 percent.
Frenkel said that an apparent air of optimism among global business and political leaders attending Davos this year was "justified" because the economic performance of each and every region of the world was better than the previous year.