How Insulin Changed the Course of Medicine

The human body is remarkably efficient when it comes to managing resources—and one of the key players in this system is insulin. This essential hormone plays a critical role in conserving energy by storing nutrients when food is abundant. Excess carbohydrates are turned into glycogen and stored in the liver and muscles, fats are packed away in adipose (fat) tissue, and proteins are built from amino acids. All of this ensures that the body has energy reserves when food isn’t readily available.

While our in-depth understanding of insulin is relatively new, the health condition it’s closely linked to—diabetes—has been documented since ancient times. Early references to symptoms of diabetes appear in Egyptian and Greek texts, proving just how long this condition has affected human health.

The islets of Langerhans (shown here in a high-power magnification), located in the pancreas, are responsible for the production of insulin.

The Road to Discovery: A History of Insulin

1869: The Islets of Langerhans

The modern story of insulin begins with Paul Langerhans, a German medical student who, in 1869, identified a cluster of previously unknown cells within the pancreas. These clusters would later be named the islets of Langerhans—the very place where insulin is produced.

1889: Linking the Pancreas to Diabetes

In 1889, German scientists Joseph von Mering and Oskar Minkowski took the next big step. Curious about the pancreas, they removed the organ from a dog. The result? The dog quickly developed severe diabetic symptoms, including high sugar levels in its urine—a key indicator of diabetes. This experiment made it clear that the pancreas played a central role in blood sugar regulation.

1921: The Breakthrough That Changed Everything

Fast forward to 1921. In Canada, a determined surgeon named Frederick Banting convinced John J.R. MacLeod, a professor at the University of Toronto, to let him use his lab during summer break. With the help of Charles Best, a young student, Banting repeated the pancreas removal experiment—but this time with a twist.

They injected one of the diabetic dogs with an extract from a healthy pancreas, and to their amazement, the dog’s diabetic symptoms improved. They had just uncovered the therapeutic power of what we now call insulin.

1922: First Human Treatment

In January 1922, the experiment reached a groundbreaking milestone. Leonard Thompson, a 14-year-old boy with type 1 diabetes, became the first human to receive insulin. The treatment worked—and it marked a turning point in medical history.

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Recognition, Controversy, and Commercialization

In 1923, the discovery of insulin earned Banting and MacLeod the Nobel Prize. However, the credit distribution sparked controversy. Banting believed Charles Best deserved equal recognition and shared his prize money with him. MacLeod did the same with James Collip, the biochemist who helped purify the insulin extract.

That same year, pharmaceutical company Eli Lilly began the mass production of insulin, making this life-saving hormone available to diabetic patients around the world.

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The Lifesaving Impact of Insulin

Before insulin, a diagnosis of type 1 diabetes was essentially a death sentence—most patients, especially children, lived only a few months after diagnosis. Today, thanks to insulin therapy, people with well-managed diabetes can live just as long and as full lives as those without the condition.

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Key Takeaways for Readers

• Insulin is a key hormone that stores excess energy and helps maintain stable blood sugar levels.
• Diabetes has been known for thousands of years, but its cause remained a mystery until the late 19th and early 20th centuries.
• The discovery of insulin in 1921 revolutionized diabetes treatment, transforming a fatal disease into a manageable one.
• Early pioneers like Banting, Best, and Collip played critical roles in making insulin therapy a global medical breakthrough.
• Today’s diabetes management tools—from insulin pumps to glucose monitors—are built on this incredible scientific foundation.

✳️ Did you know? The first insulin treatments were made using extracts from animal pancreases. Modern insulin, however, is produced using advanced biotechnology, making it purer and more effective than ever before.

💡 Worth thinking about: What other modern diseases could be drastically changed by a breakthrough as monumental as insulin?

Claude Bernard and the Discovery of Glucose Production in the Body

The foundations of modern physiology owe a great deal to the groundbreaking work of French scientist Claude Bernard. In the mid-19th century, his observations transformed how we understand glucose metabolism and the role of the liver in maintaining life.

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Early Observations: Glucose Formation During Digestion

In 1843, Bernard made an important observation while studying digestion. He found that when substances like sugar cane or starch were broken down in the body, they produced glucose—a simple sugar that could be easily absorbed into the bloodstream.

At the time, this seemed like a straightforward digestive process. However, Bernard chose not to pursue this finding immediately, setting the stage for a more profound discovery years later.

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An undated photograph of the great French physiologist Claude Bernard.

A Surprising Discovery in Blood

By 1848, Bernard returned to his earlier work with a new question in mind. He examined blood samples from animals that had been fasting for several days or were fed diets completely lacking carbohydrates.

Surprisingly, glucose was still present in their blood.

This raised a critical question:

If no carbohydrates were consumed, where was the glucose coming from?

Further investigation revealed that glucose levels were especially high in blood flowing from the liver through the hepatic vein. When Bernard analyzed liver tissues from various animals—including mammals, birds, reptiles, and fish—he consistently found glucose in the liver, but not in other organs.

This led him to a bold conclusion:

The liver plays a central role in producing glucose.

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Challenging Established Scientific Beliefs

Bernard’s findings were revolutionary—and controversial. At that time, several widely accepted ideas dominated biological science:

• Each organ was believed to have only one specific function
• The liver’s sole role was thought to be bile production
• Only plants were believed to create nutrients, not animals

Bernard’s work directly challenged all three assumptions. He proposed that the liver had multiple functions, including the ability to produce glucose internally.

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The Accidental Breakthrough in 1849

In 1849, a chance event led to a major breakthrough. Bernard analyzed a liver sample that had been left overnight from a previous experiment.

To his surprise, the glucose levels in this liver were even higher than before.

This observation provided strong evidence that the liver was not just storing glucose—it was actively producing it.

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The Discovery of Glycogen

To explain how the liver could produce glucose, Bernard proposed the existence of a storage substance made from glucose. He named this substance glycogen.

Although he initially struggled to isolate it, Bernard later identified a white, starch-like material in the liver in 1856. This substance turned out to be glycogen—the body’s stored form of glucose.

How Glycogen Works

• Glycogen is formed from glucose molecules
• It is stored mainly in the liver
• When the body needs energy, glycogen is broken down back into glucose
• This process helps maintain stable blood sugar levels

This discovery completed the understanding of a vital biological cycle:

the continuous production, storage, and release of glucose in the body.

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A New Understanding of Metabolism

Bernard’s work revealed a deeper truth about the human body:

• The body is not just a system that breaks down food
• It can also build complex substances from simpler ones
• The liver plays a central role in regulating energy balance

This marked a turning point in physiology, laying the foundation for modern research in metabolism, endocrinology, and medical science.

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Key Takeaways for Better Understanding

• The liver is not just a digestive organ—it actively produces glucose
• Glucose can be generated in the body even without food intake
• Glycogen acts as a storage form of glucose, helping maintain energy balance
• The body continuously switches between storing and releasing glucose
• Bernard’s discoveries challenged outdated scientific beliefs and reshaped biology
• Modern understanding of blood sugar regulation started with these findings
• The human body is both a builder and a user of nutrients, not just a consumer