What Is Diabetes Mellitus?

In my last entry (May 4, 2007), I discussed the diagnosis of diabetes and prediabetes. I completely forgot to first explain what diabetes is. Diabetes mellitus, or “sugar” diabetes to distinguish it from another type diabetes, diabetes insipidus, is really a group of disorders that have 3 things in common. First, all types of diabetes have insulin deficiency. Insulin is a hormone protein produced by the beta cells of the pancreas. Insulin is an amazing hormone with many actions, but simply put, it helps control the blood glucose level. In fact, as far as I know, it is the only hormone that directly lowers the blood glucose level (sometime in the future, we will discuss the many hormones that raise the blood glucose level).

What causes insulin deficiency?

There are many causes of insulin deficiency. The easiest to understand is the type of insulin deficiency because the beta cells are decreased in number or totally missing from the pancreas as in type 1 diabetes (T1DM). Type 1 diabetes is the type of diabetes that is most often diagnosed in childhood- it used to be called juvenile-onset diabetes. In most instances T1DM is a genetic disorder caused by autoimmune destruction of the beta cells. About 10% of diabetes in the U.S. is classified as T1DM.

Another kind of insulin deficiency is what I would call “relative deficiency.” This means that the beta cells are producing insulin but the person is resistant to the insulin- it just doesn’t work well. This is typically present in people who have type 2 diabetes (T2DM), the most common form of diabetes in the U.S. This form of diabetes is also inherited but in most instances requires that the person be overweight (all overweight people are somewhat resistant to insulin). It is all a bit complicated, but in most instances of type 2 diabetes there are several factors involved including insulin resistance, impaired insulin release from the pancreas in response to high blood glucose levels, and some element of actual deficiency. Anyway, the end result is not enough insulin to prevent high blood glucose levels or hyperglycemia, the second feature in all forms of diabetes.


It is not enough to have insulin deficiency (either actual deficiency, resistance to insulin action, or both) to call it diabetes. The end result must be hyperglycemia, the hallmark of diabetes. In my last entry I discussed the specific blood glucose levels that define a diagnosis of diabetes.

The third feature

The last component of all types of diabetes is a tendency to develop serious complications. Most people know something about these problems- eye disease, called retinopathy, kidney disease, called nephropathy, and nerve disease, called neuropathy. Together these three “opathies” account for much of the misery associated with diabetes and are often called “microvascular” complications even though they do not all affect the microvasculature (don’t ask me to explain that). The microvascular complications are to be distinguished from the “macrovasular” complications of diabetes, peripheral vascular disease, stroke, and heart disease.

Diabetes mellitus as a syndrome

In summary, diabetes is a group of distinct disorders that share 3 things in common- insulin deficiency, hyperglycemia as a result, and high risks for developing medical complications. There are many different types of diabetes but probably 99% are either T1DM or T2DM. Maybe sometime in the future we will discuss the other 1%. We will definitely come back to further discussions about T1DM and T2DM.

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