Insulin is a hormone produced in the pancreas, a gland located behind the stomach. Insulin is necessary for metabolism, the process that converts food into the energy your body needs.

Without insulin, glucose -- a form of sugar produced when carbohydrates (starches and sugars) are digested -- cannot be used properly. Instead, glucose builds up in the bloodstream and spills into the urine showing as sugar in the urine. Without treatment, a person with diabetes will have excessively high levels of sugar in the blood and the urine, which, over time, can cause serious complications.

Types of Insulin

There are four basic types of insulin: rapid-acting,short-acting,intermediate-acting, and long-acting. Each type differs in three ways: onset (how long after injection it begins to work); peak (how long after injection it reaches maximum effectiveness); duration (how long it continues to lower glucose levels). In general, human insulins have quicker onset than animal-based insulins. The following times are given in ranges because insulin activity varies somewhat from person to person and even from day to day.

Rapid-Acting (Insulin Analog) should be taken within 15 minutes of a meal, peaks in 1/2-hour to 1-1/2 hours, and has a duration of action from 2 to 5 hours. At the present time, this type of insulin is available only by prescription.
Short-Acting (Regular Insulin) begins to work in 1/2-hour to 2 hours, peaks in 2 to 5 hours, and has a duration of action lasting up to 8 hours.
Intermediate-Action (NPH and Lente)
begins to work in 1-1/2 to 6 hours, peaks in 4 to 14 hours, and has a duration of action lasting up to 24 hours.
Long-Acting (Ultra Lente) begins to work in 6 to 14 hours and is usually effective up to 36 hours.

Many people use combinations of these insulins for better control, combining a short-acting insulin with intermediate- or long-acting insulin, either in separate injections or mixed in a syringe. Some use pre-mixed varieties, which are available in combinations of NPH and regular insulin. Insulin is also sold in cartridges for use in insulin pens. Your health care professional will advise you of different options and help you determine what is best for you.

Storing Insulin

Expiration date: All insulin bottles carry an expiration date. Outdated insulin should not be used.
Refrigeration: Insulin does not need to be refrigerated as long as it is kept at room temperature and protected from excessive heat or cold. Extra bottles should be stored in the refrigerator to keep themat a constant, cool temperature.
Travel Tips: Keep your insulin, syringes, and other diabetes supplies with you in a carry-on bag; don't put them in checked luggage that might be lost or subjected to extreme temperatures in transit. Bring a letter from your doctor explaining the syringes in case your luggage is examined.

A Problem to Watch For

Hypoglycemia (Low Blood Sugar, Insulin Reaction, Insulin Shock):
Hypoglycemia occurs when blood sugar levels fall below normal, and can happen when the injected insulin does not exactly match the body's needs. Any of a number of factors can cause blood sugar to drop -- a missed or delayed meal, too much physical activity, or too much injected insulin. An insulin reaction can happen slowly or very quickly and, if not treated, can result in loss of consciousness. If left untreated low blood sugars can be life threatening. Most people with diabetes experience warning signs when their blood sugars drop into this danger zone.

The symptoms of low blood sugar include: headache, sweating, pale and moist skin, a cold and clammy feeling, extreme hunger, dizziness, shakiness, weakness, fatigue, rapid pulse rate, blurred vision, shallow breathing, inability to concentrate, irritability, loss of coordination, mental confusion, seizure, and loss of consciousness.

Treatment consists of immediate intake of some form of sugar, such as two to four glucose tablets, six ounces of non-diet soda, or four to six ounces of fruit juice. People taking insulin should always carry a form of fast-acting sugar to treat insulin reactions. However, nothing can be given by mouth if the person is unconscious.

Other Possible Side Effects of Insulin

Insulin Site Allergies

Local irritation and itching at the injection site may occur when a person first starts taking insulin. Usually, these allergies disappear after a few weeks. Keep your physician advised if an allergic reaction occurs.

Allergy to Insulin

Occasionally, a person with diabetes will be allergic to insulin itself. This systemic allergy requires desensitization by injections of progressively increasing concentrations of insulin.

Insulin Resistance

Insulin resistance may occur in people with Type 1 diabetes who have produced a lot of antibodies to the insulin they are taking. The newer insulins may reduce this problem. Obesity is generally the cause of insulin resistance in people with Type 2 diabetes.

Atrophy & Hypertrophy