The introduction of insulin is one of the most impactful medical developments of the 20th century. Insulin is a hormone produced by the pancreas that allows the body to use sugar from carbohydrates for energy or to store for future use. For individuals with type 1 diabetes, whose bodies cannot produce insulin, its discovery meant the difference between life and death, catalyzing a century of innovation in diabetes care.
The Discovery of Insulin
Before 1922, a diagnosis of what is now known as type 1 diabetes was a death sentence. The primary method of management was a “starvation diet,” a severe restriction of carbohydrates designed to minimize blood sugar levels. While these diets, some prescribing as few as 450 calories a day, could extend a patient’s life by a few years, they often led to death from starvation itself. The lives of those diagnosed, often children, were short and marked by extreme thirst, hunger, and systematic wasting.
In 1921, a University of Toronto team including surgeon Frederick Banting, student Charles Best, and biochemist James Collip, worked under Professor J.J.R. Macleod to isolate the pancreatic secretion that regulates blood sugar. Their experiments involved tying off the pancreatic ducts of dogs, leaving the insulin-producing islet cells intact. They then extracted a substance from these islets.
The team tested this extract on diabetic dogs, observing a significant drop in their blood sugar. James Collip then led the effort to purify the extract to make it safe for humans, which was necessary to reduce side effects.
The first human trial took place in January 1922 on 14-year-old Leonard Thompson, who was near death from diabetes. An initial injection caused an allergic reaction, but after Collip further refined the extract, a second injection proved successful. Thompson’s blood sugar dropped to near-normal, and his health dramatically improved. Recognizing the global need, the researchers sold the patent to the University of Toronto for $1 each, ensuring companies like Eli Lilly could rapidly scale production.
Evolution of Insulin Formulations
The first commercially available insulins were derived from cow and pig pancreases. These animal-derived insulins were often impure, leading to allergic reactions, and were short-acting, requiring frequent daily injections to manage blood glucose.
A leap forward occurred in the late 1970s with recombinant DNA technology, which used bacteria to produce synthetic “human” insulin. First marketed in 1982 as Humulin, this biosynthetic insulin was structurally identical to the human hormone. Its higher purity reduced the allergic reactions associated with animal insulins.
The next advancement in the 1990s was the creation of insulin analogs, where genetic engineering was used to modify human insulin’s structure. This altered its absorption rate and duration of action. This led to rapid-acting analogs, such as insulin lispro (1996), to cover mealtime blood sugar spikes.
Conversely, long-acting analogs like insulin glargine (2000) were designed to provide a steady, peakless release of insulin over 24 hours. This mimicked the body’s basal insulin secretion. These analogs allowed for more flexible and precise diabetes management by better replicating natural insulin physiology.
Advancements in Insulin Delivery
Insulin administration has evolved significantly. Initially, patients used large, reusable glass syringes with needles that required boiling. Disposable plastic syringes, introduced in the mid-1950s, were a major improvement in convenience and safety.
The first insulin pen arrived in 1985, offering greater accuracy, portability, and discretion than vials and syringes. These devices contain an insulin cartridge and use a dial-up mechanism for dosing. Pre-filled, disposable pens later simplified the process even more.
Insulin pumps were developed to more closely mimic the body’s natural insulin release. The first commercial pumps became available in the late 1970s, offering continuous subcutaneous insulin infusion (CSII). This technology uses a computerized device to deliver a continuous trickle of rapid-acting insulin through a thin tube under the skin.
Modern pumps allow users to program different basal rates and deliver larger doses (boluses) for meals, providing more precise glucose management. The technology has continued to shrink in size, with some pumps now being small, tubing-free patches that adhere to the skin.
Living with Insulin Today
Modern insulin therapy integrates advanced technology to reduce the daily burden of diabetes management. A key development is pairing insulin pumps with Continuous Glucose Monitors (CGMs), small sensors that track glucose levels around the clock.
This pairing created hybrid closed-loop systems, or an “artificial pancreas.” An algorithm analyzes CGM data and automatically adjusts the pump’s basal insulin delivery. The system can suspend delivery to prevent low blood sugar or increase it to prevent high blood sugar.
While users still input carbohydrates for meals, these systems automate many adjustments, increasing time in the target glucose range. This reduces the frequency of severe high and low blood sugar events.
Despite a century of progress, challenges persist. The high cost and inconsistent accessibility of insulin remain significant issues, forcing some individuals to ration their supply—a dangerous practice. Daily management still requires meticulous carbohydrate counting and vigilance to prevent hypoglycemia (low blood sugar).