the invention of insulin

The invention of Insulin

Insulin was discovered by Sir Frederick G BantingCharles H Best and JJR Macleod at the University of Toronto in 1921 and it was subsequently purified by James B Collip.

Before 1921, it was exceptional for people with Type 1 diabetes to live more than a year or two. One of the twentieth century’s greatest medical discoveries, it remains the only effective treatment for people with Type 1 diabetes today.

On 11 January 1922, Leonard Thompson, a 14-year-old boy with diabetes, who lay dying at the Toronto General Hospital, was given the first injection of insulin. However, the extract was so impure that Thompson suffered a severe allergic reaction, and further injections were cancelled.

Over the next 12 days, James Collip worked day and night to improve the ox-pancreas extract, and a second dose was injected on the 23 January. This was completely successful, not only in having no obvious side-effects, but in completely eliminating the glycosuria sign of diabetes.

A dramatic moment

Children dying from diabetic ketoacidosis (DKA) were kept in large wards, often with 50 or more patients in a ward, mostly comatose. Grieving family members were often in attendance, awaiting the (until then, inevitable) death. 

In one of medicine's more dramatic moments Banting, Best, and Collip went from bed to bed, injecting an entire ward with the new purified extract. Before they had reached the last dying child, the first few were awakening from their coma, to the joyous exclamations of their families.

How it started - great minds came together

By 1920 scientists had already pinpointed clusters of cells in the pancreas, called islets, that produce insulin and worked out that it’s these cells that are destroyed in type 1 diabetes. Understanding the cause of type 1 diabetes meant researchers now had a chance of treating the condition. Attempts had been made to extract insulin from ground-up pancreas cells, but they’d all proved unsuccessful. The challenge was to find a way to extract insulin from the pancreas without it being destroyed in the process. 

In October 1920, Frederick Banting – a Canadian surgeon – read an article that suggested insulin-producing cells in the pancreas are slower to deteriorate than other pancreas tissue. Banting realised that this might allow for the removal of insulin by breaking down the pancreas in a way that would leave just the cells that produce insulin intact. But Banting wasn’t a scientist and knew he couldn’t test his theory alone. On 7 November 1920 he paid a visit to a top professor at the University of Toronto, John Macleod. They put their minds together and began to work on a plan.  


Macleod provided Banting with the labs needed to conduct their experiments and brought in a research student, called Charles Best, to help out. Best specialised in testing blood to check glucose levels. This would be the way they would know whether their insulin extracts were having any benefit.  

On 17 May 1921 Banting, Best and Macleod first got together to begin their research and set about figuring out how to remove insulin from a dog’s pancreas. Their method involved tying off the pancreatic duct to kill off other substances in the pancreas that would destroy insulin, but leave the islets intact. The remaining extract would then be given to other dogs who didn’t produce any of their own insulin because their pancreases had been removed to work out its effects on their blood sugar levels. Progress was initially slow and while many of their experiments failed, Banting and the team saw regular drops in blood sugar levels as a result of their extract, and were confident they were on to something big. By November, they’d successfully treated a dog with diabetes with their insulin extract for 70 days.  

James Collip joins 

In Dec 1912 James Collip, a biochemist, joined the group to work on purifying insulin so it would be safe enough to be tested in humans. With his help, a more concentrated and pure form of insulin was developed, this time from the pancreases of cattle. 

In January 1922, Leonard Thompson, a 14-year-old boy dying from type 1 diabetes, became the first person to receive an injection of insulin. Within 24 hours, Leonard’s dangerously high blood sugar levels dropped, but he developed an abscess at the site of the injection and still had high levels of ketones.  

Collip worked day and night on purifying the extract even further, and Leonard was given a second injection on 23 January 1922. This time it was a complete success and Leonard’s blood sugar levels become near-normal, with no obvious side effects. For the first time in history, type 1 diabetes was not a death sentence. 

And today we thank them, for Diabetes type 1 is definately not a death sentence. 

All of us at The Diabetes Kitchen say thank you - so very much.

(We thank Diabetes UK for much of this information).



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