A Quick Guide to Insulin, the Key to Glucose
Diabetes is, in a sense, all about insulin. The hormone is central to both the development of the disease and its treatment. Here is a primer on insulin: what it is, what it does, and how it's essential to health.
A Hormone's Work
Insulin's main task is to help turn carbohydrates from food into the energy that keeps the body running. After they are eaten, carbs are broken down into the sugar glucose, which then enters the bloodstream for distribution. Beta cells in the pancreas detect the rise in blood glucose and produce insulin in response. The hormone travels around the body in the blood, signaling to cells all over that soup's on and it's time to let glucose in. Insulin is the "key" that opens the cells to glucose.
As insulin does its work and cells gobble up glucose, blood glucose levels begin to fall. The beta cells detect this drop in blood glucose and taper off the flow of insulin. This ensures that the glucose in the blood will plateau at a healthy level and not go too low. The absence of insulin in the blood is also a signal that the body hasn't eaten for a while and should tap fat stores instead of glucose for its energy needs.
Though its job is being a hormone, insulin is also a protein, manufactured by the body using information written in the genes. The beta cells are the only cells in the body with the natural capacity to make insulin. This specialization means that the beta cells are the body's last and only hope for regulating blood glucose levels on its own.
Insulin in Diabetes
Diabetes develops when the beta cells fail to produce enough insulin to keep blood glucose levels in a healthy range. In type 1 diabetes, the beta cells are destroyed by the body's own immune system gone haywire. In type 2, cells are resistant to insulin, and the beta cells fail to produce enough of the hormone to compensate. The goal of diabetes treatment is to normalize blood glucose levels by either increasing levels of insulin in the body or sensitizing the body to insulin.
All people with type 1 and some with type 2 require treatment with insulin to control blood glucose. There are two basic kinds of insulin used to manage diabetes: mealtime and background (long-acting). Mealtime insulin works fast and, as the name suggests, is taken just before eating to deal with the subsequent surge in blood glucose as food is digested. Background insulin is usually taken once a day and keeps blood glucose down between meals. While both mealtime and background insulins are essentially the same protein, almost identical to the version made by the body, the medicines are formulated differently in the lab to speed or slow their absorption, respectively. Oral medications for type 2 diabetes work by either boosting the production of insulin by the beta cells or making the body less resistant to insulin.
Insulin can't be taken orally because, as a protein, it would be destroyed by digestive enzymes. Instead, it must be put into the body's tissues by syringe, pen, or pump. All of these approaches deliver insulin just under the skin. From there, it diffuses to the bloodstream, where it goes to work.
Researchers are developing better and easier ways to deliver insulin and more closely match the body's need for it. A so-called artificial pancreas (using software to link a continuous glucose monitor and an insulin pump) would automatically dose insulin based on blood glucose measurements. Scientists are developing injected insulins that work either faster or slower than existing versions to help people with diabetes more precisely control their blood glucose levels. Others are working on an oral form of insulin, the elusive insulin pill, as well as versions of the medication that can be inhaled.
In people who don't have diabetes, the beta cells do an essentially perfect job of doling out insulin and regulating blood glucose. When using insulin as a medication, it is extremely difficult to achieve this precision. In people with diabetes, the amount of insulin in the body is not always ideal, which means that blood glucose control isn't perfect either. A common problem is too much insulin for a given blood glucose level. That causes the cells to absorb too much glucose from the blood, leaving a person with low blood glucose (hypoglycemia).
Medical science has come a long way, though. Someday, science may catch up with biology, making insulin and blood glucose levels in people with diabetes perfect, too.