In a research note to clients, UBS Strategist Stephen Caprio argues that investor confidence — evidenced by high stock market valuations — may may be misplaced, given a recent slowdown in bank lending.

U.S. bank loan growth by domestic banks is falling in nearly almost category, most especially "commercial and industrial" loans. Caprio points out that this decline is not being made up by higher growth in corporate bond issuance, and is being driven mostly by a lack of demand for borrowing.

Why it matters: Companies are issuing less debt due to a mix of uncertainty regarding tax and spending policy, already high debt levels in the U.S. corporate sector, and the threat of higher interest rates. Investors are counting on stronger global growth to help U.S. companies overcome these headwinds, but they may be discounting the chances that some sort of shock — like the 2014 oil price collapse — constrains growth and triggers a stock market pullback or correction.