Dr. Donald F. Steiner, a researcher whose discoveries transformed scientists’ understanding of insulin and other hormones and led to major improvements in the treatment of diabetes, died on Nov. 11 at his home in Chicago. He was 84.

A cousin, Steven Roess, confirmed the death. Until recent hip surgery, Dr. Steiner had continued to conduct diabetes research at the University of Chicago.

Dr. Steiner spent most of his career studying insulin, a hormone made by the pancreas that enables cells to take in sugar to use as fuel or to store. People who lack insulin, or cannot use it properly, develop diabetes, in which sugar builds up in the bloodstream and can cause an array of complications, including heart disease, strokes, kidney failure, blindness and amputations.

About 29 million Americans have diabetes, according to the Centers for Disease Control and Prevention.