Central banks need to reconsider whether bond purchases are the best way to stimulate growth when interest rates are low, especially after recent asset purchases left them nursing heavy losses, a senior European monetary policymaker has said.

Isabel Schnabel, who oversees bond-buying at the European Central Bank, said in a speech on Tuesday that central banks “need to carefully assess whether the benefits of asset purchases outweigh the costs”.

Schnabel said central banks’ asset purchases — also known as quantitative easing — had “played an important role in stabilising markets at times of stress”. But she added their effectiveness in stimulating demand depends on the economic conditions at the time of the purchases and “can come with costs that might be higher than those of other policy instruments”.