A dozen German life insurance companies wouldn’t be sufficiently funded to face even a mild stress scenario in which German government bond yields decline further and stay super low, according to a paper released Monday by Germany’s central bank.

“The present analysis shows that a persistent low-interest-rate environment harbors a potential risk to the stability of the life insurance segment,” a pair of Bundesbank economists wrote in a study looking at year-end 2012 data from 85 German life insurers.