Most likely, you knew very little about diabetes before you learned that you had it. After your diagnosis, your next few doctor visits were probably a crash course in diabetes: learning how to check your blood glucose level, inject insulin or follow a schedule for taking pills, adjust your eating habits, etc. Your doctor may also have mentioned what diabetes is and what causes it in this blitz of information, but with so much to learn at once, you may not remember what he said — or remember him saying anything at all on these topics.
It can be difficult to take in so much new information at one time, especially when you are just learning diabetes terminology and adjusting to the idea of having diabetes; many people find they miss a lot of the background information about the underlying causes of their diabetes. However, understanding how and why diabetes develops can help you to be an active member of your diabetes-care team.
The two main types
Diabetes mellitus, usually referred to as just diabetes, is characterized by a high blood glucose level. There are several different types of diabetes, each with a unique underlying cause. The most common forms are Type 1 diabetes and Type 2 diabetes. Both are considered chronic diseases, meaning that once diagnosed, they don’t go away. Blood glucose levels that are higher than normal but not high enough to be diabetes are now called prediabetes. For descriptions of other types of diabetes and related conditions, see “Types of Diabetes.”
Type 1 diabetes used to be called juvenile or insulin-dependent diabetes, and Type 2 diabetes was called adult-onset or non-insulin-dependent diabetes. The American Diabetes Association now favors the terms Type 1 and Type 2 diabetes, which are defined based on the underlying cause of the diabetes, not on a person’s age at diagnosis or treatment method.
Type 1 diabetes
Type 1 diabetes occurs when the body’s immune system launches an attack against the insulin-producing beta cells in the pancreas. Why the immune system does this is not completely understood, but it is thought that both genetics and some sort of environmental trigger are involved.
Certain combinations of genes make some people more likely to develop Type 1 diabetes, but having a genetic tendency alone is not enough: Not everyone at increased risk for Type 1 develops it. For instance, in identical twins (who by definition have the exact same genetic makeup), when one twin has Type 1 diabetes, the other twin also develops it only 50% of the time. It is believed that for a genetic tendency toward Type 1 to be “expressed,” a person must be exposed to an environmental “trigger” that sets the autoimmune process in motion. Many potential triggers have been proposed, including viruses, bovine serum albumin (a protein in cow’s milk), hormones, and environmental toxins, but none have been definitively proven to lead to Type 1 diabetes.
Once the process is set in motion, the immune system produces antibodies to beta cells and to insulin and begins to destroy them. (Under normal circumstances, antibodies seek out and flag harmful foreign substances within the body, such as bacteria or viruses, for destruction.) This process starts many years before diabetes is diagnosed. In fact, it’s possible to identify people at risk of developing Type 1 diabetes by checking their blood for antibodies to beta cells and to insulin.
Over time, the quantity of insulin produced by the pancreas and the amount circulating in the bloodstream progressively decline. The resulting signs and symptoms of Type 1 diabetes, which include high blood glucose levels, weight loss, increased urination, hunger, and thirst, and large amounts of ketones in the blood and urine, generally occur only after a majority of the beta cells have been destroyed.