Glucose-sensitive cell protecting agent

Provided is a means for reducing adverse effects of a high glucose concentration on the living body. Provided are: a preparation for protecting glucose-sensitive cells from glucose toxicity caused by a high glucose concentration, the preparation containing N-acetyl-D-mannosamine; a pharmaceutical composition for protecting glucose-sensitive cells from glucose toxicity caused by a high glucose concentration, the pharmaceutical composition containing an effective amount of N-acetyl-D-mannosamine and a pharmaceutically acceptable carrier; a use of N-acetyl-D-mannosamine to prepare a drug for protecting glucose-sensitive cells from glucose toxicity caused by a high glucose concentration; and a method for protecting glucose-sensitive cells from glucose toxicity caused by a high glucose concentration, the method including a step for administering an effective amount of N-acetyl-D-mannosamine to a subject in need thereof. The glucose-sensitive cells are selected from the group consisting of nerve cells, renal cells, and vascular endothelial cells.