Insulin, a hormone that regulates sugar levels in the body, was first discovered in 1889 by German physiologist Oskar Minkowski (1858–1931) and German physician Joseph von Mering (1849–1908). They observed that the removal of the pancreas caused diabetes in dogs. Researchers set about isolating the substance but it was not until 1922 that insulin was used to treat diabetic patients. The first genetically engineered human insulin was produced by American scientists in 1978.