In any discussion of diabetes, the word insulin is almost certain to come up. That’s because a lack of insulin or trouble responding to insulin (a condition called insulin resistance) or both is what is responsible for the high blood glucose levels that characterize diabetes.
Thanks to years of medical research, however, endogenous insulin (that produced by the pancreas) can be replaced or supplemented by exogenous insulin (insulin produced in a laboratory). For people with Type 1 diabetes, injecting insulin (or infusing it with an insulin pump) is necessary for survival: Before the discovery of insulin in 1921, the life expectancy for a person diagnosed with what was then known as juvenile diabetes was less than a year. For some people with Type 2 diabetes, using insulin may be the best — or only — way to keep blood glucose levels in the recommended range, and maintaining blood glucose control is one of the most important things you can do to lower your risk of developing potentially devastating complications.
But even if you never have to take insulin to control your diabetes, it is important to understand what insulin is and what it does in the body. That’s because your lifestyle choices affect the health of your insulin-producing beta cells. Making an effort to lose excess weight, eat healthfully, exercise regularly, and take any prescribed drugs as instructed can prolong the life of your beta cells, so they continue to make the insulin you need.
The role of insulin
Insulin is a hormone that is released by the beta cells of the pancreas, a glandular organ located in the abdomen, in response to a rise in the level of glucose in the blood. Blood glucose levels rise when a person consumes carbohydrate-containing food or drinks, as well as during periods of physical and sometimes mental stress. Insulin prevents a further increase in the blood glucose level and causes it to fall gradually by enabling the glucose to enter the body’s cells, where it is burned for energy or stored as glycogen or fat for later use. While many hormones raise blood glucose levels, only insulin lowers them.
The body needs a small amount of insulin at all times to keep blood glucose levels controlled between meals and overnight. In a person who does not have diabetes (or who does have diabetes but whose pancreas still produces insulin), the pancreas constantly secretes this small amount of so-called background, or basal, insulin. A person whose pancreas does not produce insulin (or does not produce enough) can compensate by injecting an intermediate- or long-acting insulin or by using an insulin pump that is programmed to continuously deliver small pulses of short- or rapid-acting insulin.
At mealtimes, blood glucose levels rise as carbohydrates are broken down to glucose and other simple sugars and enter the bloodstream. A healthy pancreas responds by releasing a burst of insulin in two phases, the first occurring almost as soon as food is eaten and lasting about 15 minutes, and the second occurring more gradually over the next 1 1/2–3 hours. In a person who doesn’t have diabetes, the amount of insulin released matches the rise in blood glucose. In people with Type 2 diabetes, a diminished first-phase insulin response is often the first sign of pancreatic insufficiency.
People who use insulin can match the pancreas’s action by injecting a dose of short- or rapid-acting insulin before the meal or by taking a bolus dose with an insulin pump. Since the goal is to match the premeal insulin dose to the expected rise in blood glucose following the meal, and since the amount of carbohydrate in the meal predicts the rise in blood glucose, the current practice is to match the premeal insulin dose to the amount of carbohydrate in the meal. This requires knowing your insulin-to-carbohydrate ratio — or how much insulin you need to “cover” a certain number of grams of carbohydrate. Your diabetes care team can help you determine your insulin-to-carbohydrate ratio by looking at your food records and your blood glucose monitoring records for before-meal and after-meal blood glucose levels. They will also take your overall insulin requirements into consideration.