In 1922, the Canadian physiologists Fred Banting and Charles Best announced to the world that they had discovered Insulin and successfully used it to treat diabetes in a human patient. Until then, diabetics would struggle to grow and there was no successful treatment. They would become walking skeletons and die prematurely due to severe weight loss.

Diabetes mellitus had been known since ancient times. Egyptian writings from as early as 1500BC described a wasting disease in which the sufferer produced sweet-tasting urine. From the 1850's onwards, autopsies of people who had died from diabetes suggested that the problem was caused when the pancreas did not function properly. Many physicians speculated that specialised cells, called the islets of Langerhans, produced a chemical that allowed the body to regulate its blood sugar level. Diabetes was caused when this chemical was not produced.

Banting and Best worked in the University of Toronto. They removed the pancreas from dogs which then developed diabetes. Their experiments may seem cruel today but without them, insulin would never have been found as the treatment for diabetes.

New methods of testing blood sugar levels allowed Banting and Best to accurately determine the effects of their treatments. They struggled to purify the chemical hormone produced by the pancreas and extracted many compounds from the islets of Langerhans. These were injected into the diabetic dogs to try and find the hormone that would reverse their diabetes.

Initially the injections were very impure and often had fatal side-effects. A team of researchers were recruited and eventually they were able to make an extract from the islets of Langerhans that was pure enough to try on a human patient. In May 1922, fourteen-year-old Leonard Thompson was successfully treated in Toronto Hospital with the extract that they called insulin. In 1928, Oskar Wintersteiner proved that insulin was a protein.

We now know that insulin allows the cells of the body to take in sugar from a digested meal. The liver is especially important in the process of regulating the body's blood sugar level. Insulin enables the liver to take in sugar (glucose) after a meal and store it as glycogen. This is used later to return glucose to the blood when blood sugar levels begin to fall.

You can find out more about insulin in Hormones and There Effects.

News of Banting and Best's success spread quickly and soon their laboratory was unable to meet the demand for the new wonder drug.

Commercial preparation of insulin began by extracting it from the pancreas of slaughtered cows and pigs. This is still an important source of insulin for medical use. Chemical modifications tailor the insulin to mimic the human hormone and also give it properties that make it convenient to administer. Early insulins were injected three or four times a day, just before each meal. More long-acting insulins have been developed so that the need to inject so often has been reduced.

In 1955 the Nobel Prize-winner Frederick Sanger found the amino acid sequence of human insulin. This allowed a human insulin gene to be made which was then used to genetically engineer bacteria that could produce large amounts of highly pure human insulin. Currently there are 1.4 million people in the UK who successfully control their diabetes by using injections of insulin and much of it is made by genetically-engineered bacteria.