Updated July 25, 2006

Understanding Insulin

by Laura Hieronymus, M.S.Ed., A.P.R.N., B.C.-A.D.M., C.D.E., and Patti Geil, M.S., R.D., C.D.E.

Types of diabetes
In Type 1 diabetes, an autoimmune process destroys the insulin-producing beta cells of the pancreas, leaving it unable to make insulin. People with Type 1 diabetes must therefore inject or infuse insulin for survival. While some people appear to have a genetic predisposition to develop Type 1 diabetes, exactly what sets off the autoimmune destruction of the beta cells is unknown.

In Type 2 diabetes, some degree of insulin resistance is typically present. Initially, the pancreas may release more insulin than normal to compensate for the insulin resistance, but eventually, the pancreas is believed to “burn out” from overproduction, and blood glucose levels rise. However, treatments other than insulin therapy are usually tried first for Type 2 diabetes. In most cases, insulin resistance can be improved with moderate weight loss, so treatment recommendations generally include lifestyle adjustments such as changes in diet and increased physical activity. Oral blood-glucose-lowering medicines are also often used in the treatment of Type 2 diabetes. (These oral medicines are not insulin.) If dietary changes, increased physical activity, and oral medicines are unable to keep blood glucose levels adequately controlled, insulin therapy may be added to the diabetes treatment regimen or substituted for the oral drugs.

Diabetes and pregnancy
In any pregnancy, the need for insulin dramatically increases around the 16th week of gestation. From then on, more and more insulin is necessary to maintain normal blood glucose levels as the pregnancy progresses.

In women with Type 1 diabetes who are pregnant, careful blood glucose monitoring to adjust insulin doses is necessary over the course of the pregnancy. In women with Type 2 diabetes, insulin is usually the drug of choice to manage blood glucose levels during pregnancy and also requires adjustments, as needed, throughout the pregnancy. Women with Type 2 diabetes who are taking oral blood-glucose-lowering medicines prior to pregnancy are urged to plan their pregnancy and, typically, to begin using insulin prior to conception. While a few studies have examined the use of oral diabetes drugs during pregnancy, many health-care providers feel they do not yet know enough about the effect of these medicines on the fetus to advocate their use at this time.

A temporary type of diabetes that complicates about 7% of all pregnancies among women not diagnosed with either Type 1 or Type 2 diabetes is called gestational diabetes. The high blood glucose levels that occur in gestational diabetes are usually first recognized around the 24th to 28th week of pregnancy. They are due to increased insulin resistance, which is generally caused by the pregnancy hormones as well as the weight gain that normally occurs in pregnancy. About 75% of women with gestational diabetes can maintain normal blood glucose levels by making lifestyle changes, such as following a meal plan and getting regular physical activity. However, if blood glucose levels remain too high, insulin is currently the drug of choice for treatment for gestational diabetes.

Synthetic insulin
Insulin that is used in diabetes treatment is not and never was extracted from human pancreases (although earlier forms of insulin were, in fact, extracted from pig and cow pancreases). Human insulin is manufactured using recombinant DNA technology (often called genetic engineering) in a laboratory; it is identical in structure to what a human pancreas produces. Insulin analogs, which are structurally different from human insulin, are also manufactured in labs using similar processes.

Also in this article:
Treating Hypoglycemia

Patti Geil and Laura Hieronymus are certified diabetes educators and diabetes health consultants in Lexington, Kentucky. They are part of the education team at an American Diabetes Association–recognized education service at Drs. Borders & Associates, PSC. The authors would like to acknowledge the expertise and contribution of their colleague, Stacy Griffin, Pharm.D., R.Ph.

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