There are two distinct types of diabetes: juvenile (type 1) diabetes and adult-onset (type 2) diabetes.  Because the causes and treatments of each is different, you need to know which one you have.

Both types of diabetes result in high blood sugar but for different reasons. In juvenile diabetes an autoimmune reaction to a viral infection damages the insulin producing cells—the “beta cells” of the pancreas–so that they make less than normal amounts of insulin. In adult onset diabetes, you produce plenty of insulin but your muscles stop responding to it—“insulin resistance.” As a result your beta cells have to produce more than normal amounts of insulin to keep your blood sugar levels down. Years of overwork eventually wears out those cells, your blood sugar rises and you develop diabetes. Your beta cells still make plenty of insulin but not enough to overcome the insulin resistance.

Generally, if your diabetes came on before age 30, you probably have juvenile diabetes. If it came on after age 40, most likely have type 2 diabetes, the usual adult onset kind. However, there are exceptions. Most notably, approximately 10 percent of patients whose diabetes comes on in later life have the juvenile type. It’s important to recognize this because it is treated differently than type 2 the usual adult-onset kind. 

Ideally, the best way to tell which kind of diabetes you have would be to measure the amount of insulin you produce. Juvenile diabetics make less than normal; adult-onset diabetics make more than normal. The problem is that insulin disappears from the bloodstream so fast it’s difficult to tell how much you produce with a blood test. Scientists have ways do it, but they’re too complicated for general use.

There is an easier way to determine which type of diabetes you have: measure your belly. Because the fat cells in your abdomen are more sensitive to insulin than those in other parts of your body, excess insulin—hyperinsulinemia–brings on belly fat. Using computerized scanners to correlate the amount of abdominal fat with the risk of adult-onset diabetes scientists found that you can estimate your risk almost as accurately as you can with a scanner by simply measuring the circumference of your abdomen with a tape measure. If your girth at the level of your navel is more than half your height, you probably have type 2, the usual adult-onset kind.

Other signs of hyperinsulinemia include high blood levels of a type of fat called triglyceride and low levels of HDL, “good cholesterol.” You can probably get the results of these tests with a call to your doctor’s office. If you have none of these signs and you don’t have much belly fat, you should consider the possibility that you have type 1, the juvenile kind, even if your diabetes came on after age 40.