100 years of insulin

Diabetes was once an uncommon disease, but it became more common during the latter part of the 20th century. Now one in 10 Americans have developed this lifelong, progressive condition. Fortunately, a diagnosis doesn't always lead to morbidity and mortality like it used to, thanks to the discovery of insulin.

University of Michigan Health's Israel Hodish, M.D., Ph.D., professor of metabolism, endocrinology and diabetes with a focus on type 2 diabetes management, discusses how the drug works, its history and why it's so expensive.

What is insulin, and what does it do in your body?

Hodish: The endocrine system is like the FBI of the body. It watches everything and tries to keep everything in balance, or homeostasis.

Hormones like insulin typically serve many functions, not just one. Insulin is a protein secreted from the abdomen, the pancreas, and among its multiple functions it helps manage blood sugar. When our blood sugar is high from the foods we eat, we secrete more insulin to try and counteract those high levels. Sugar isn't bad – our cells need sugar.  In normal situations, we get sugar in similar parts from what we eat and what we make in our liver.

Insulin helps sugar in our blood get into many cells in the body. The main tissues that use insulin are liver, fat and muscle cells.

Most people can keep their blood sugar levels stable because the balance of sugar in our food, sugar made by our liver and the hormones that we secrete keep it stable. However, people with diabetes of any type, have difficulty keeping their blood sugar stable because an insufficient amount of insulin is secreted from their pancreas, causing sugar to stay in the blood instead of entering cells. When the sugar stays in the blood and blood sugar levels remain high over a period of time, this can cause serious health issues and increase a patient's risk of heart disease, kidney disease, eye disease, other organs' damage and importantly premature death.

What's the relationship between insulin and diabetes?

Hodish: Before insulin, diabetes was a fatal disease. It mostly affected children, and they would die a few months later. Physicians only knew how to diagnose it by tasting children's urine. If the urine was sweet, the child had diabetes. They didn't know how to treat it, though, until investigators in Toronto, Canada were able to extract material from an animal's pancreas and inject it into children. They called it insulin.

Later, it was found that the pancreas contained a limited number of cells called beta cells that are specialized for making insulin. We learned that the destruction of the cells by inflammation or the body demanding more insulin than the cells can produce, causes diabetes.

However, insulin isn't always as simple as you make enough, or you don't. Healthy people secrete different amounts of insulin based on their biology and the amounts changes over time. For example, pregnant women and adolescents require and secrete more insulin compared to other adults. In some areas of the world where there's less food, people survive by partial insensitivity to some of their insulin functions.

During the second half of the 20th century, the weight of the population gradually increased and with that, so did its insulin needs. Many people became resistant to some of the functionalities of the insulin hormone and thus need to secrete more insulin to maintain normal blood sugar levels. But in the Western world, about one in five people with this kind of selective insulin resistance cannot produce enough insulin to meet the body's needs and consequentially become insulin deficient. When there is not enough insulin, blood sugar goes up and type 2 diabetes starts.

Most people that are overweight don't have diabetes.  A person doesn't have to be obese to develop diabetes, but if they weigh a little more than their ancestors, like their parents, then they are more susceptible. In many cases, the pancreas can't keep up. We know lifestyle choices play into the development of diabetes, but so does genetics, age and weight. It's nobody's fault that this happens; diabetes isn't anyone's choice. It's not a punishment for being overweight.

How has the discovery of insulin changed the way someone can live with diabetes?

Hodish: Diabetes can affect many organs in the body and the main predictor of this organ damage is high blood sugar. High blood sugar is a key indicator of someone with diabetes having complications later on or dying prematurely, and insulin helps balance these levels. In fact, someone with diabetes who manages their blood sugar well on a regular basis can live as long as people without diabetes. If insulin therapy is needed, it can also be achieved if the right amount of insulin at the right times is taken.