When a person consumes carbohydrates, the nutrient is broken down into a simple sugar called glucose, which is absorbed into the bloodstream. Glucose is the body’s primary energy source.

Insulin is a hormone that helps move glucose from the bloodstream into the cells of the body. Insulin is produced by specialized beta cells in a part of the pancreas called the islets of Langerhans. When the body cannot produce enough insulin or fails to respond properly to it, the condition is known as diabetes.

The pancreas also produces a hormone called glucagon that acts contrary to insulin by raising levels of glucose in the bloodstream as needed.

Insulin levels can become too high or too low. In type 1 diabetes, the pancreas produces virtually no usable insulin. People with this condition depend on insulin injections to live. In people with type 2 diabetes, the cells are insulin-resistant, meaning they have difficulty absorbing insulin and, consequently, glucose.

In both cases, elevated levels of glucose in the blood causes symptoms of diabetes (e.g., excessive thirst, hunger, fatigue) and may lead to serious complications, such as nephropathy (kidney disease), retinopathy (eye disease) and cardiovascular disease.

About 12 percent of American diabetic patients (1.7 million) take insulin and antidiabetic agents, and 16 percent (2.1 million) take insulin only, according to the Centers for Disease Control and Prevention. The proportion of those taking only insulin has declined in recent years, and the number of those taking antidiabetic agents only or insulin and antidiabetic agents has risen.

Insulin treatments maintain glucose levels that are normal and that will not trigger symptoms. Though patients can obtain most forms of insulin without a prescription, a physician should always be consulted when developing a dosage level and treatment regimen. Insulin can be delivered via several different methods, including:

• Subcutaneously (under the skin)
• Intramuscularly (into muscle)
• Intravenously (into a vein)
• Orally (inhalation through the mouth to the lungs)

Insulin is not swallowed because stomach acid destroys it, though researchers are trying to create insulin pills that overcome this obstacle.

Optimal places to inject insulin include the abdomen, upper arms, thighs, hips and calves. Different locations on the body absorb insulin at different rates. The preferred site is the abdomen because the insulin is absorbed most consistently. The optimal sites after the abdomen are the arms, thighs and hips.

Each injection site should be about a half-inch from the location of the previous injection to prevent the erosion of fat beneath the skin (lipodystrophy). Rotating the injection site within the same site location will ensure that insulin is absorbed at a more constant rate. The same injection site should be used no more than once a month.

Insulin can be delivered via needle-and-syringe injections, insulin pen, jet injector or insulin pump. The U.S. Food and Drug Administration (FDA) and European regulators approved the first form of inhaled insulin 2006. Other methods are being developed.

The amount of insulin a patient requires depends upon factors such as diet, exercise and weight. Methods include:

• Needle and syringe, or cartridge or prefilled pen injection. Insulin is injected into the fat just beneath the skin. Insulin pens use cartridges filled with insulin that are inserted into a device that resembles a pen. The insulin pen is convenient for travel and for use at school or work.
  
  

  

• Insulin jet injectors. These devices use a high-pressure air mechanism to push a fine stream of insulin into the skin. Many who use this method say it is less painful than needle-and-syringe injections.
  
  
• Insulin pumps. These small, computerized delivery devices are usually worn on a belt or inside a pocket. About the size of a pager, insulin pumps have a small, flexible tube attached to a thin needle. The needle is inserted into the abdomen and taped into location. The needle requires cleaning and reinsertion every few days. Pumps deliver a continuous flow of rapid-acting insulin. Surgically implanted insulin pumps are less readily available

• Inhaled insulin. Powdered insulin is inhaled through the mouth with a special inhaler. The medication travels to the lungs and is absorbed into the bloodstream. Some people using inhaled insulin, especially those with type 1 diabetes, must still inject long-acting insulin.

It is crucial that patients properly store insulin and use it only if it is still good. Patients are advised to consult with their pharmacist or physician for specific instructions on insulin storage. Generally, insulin should be kept in the refrigerator and should not be frozen. Insulin that is frozen, heated or outdated should be discarded. Depending on the type of insulin, an appearance that is cloudy, clumped or crystallized may also be a reason to get rid of the medication. However, intermediate-acting and long-acting insulins are normally cloudy.

If refrigeration is not available, insulin should be kept in a dry place at room temperature and out of sunlight. Once it is opened, manufacturers generally recommend that insulin should be used within 28 days whether it is refrigerated or not. Insulin should not be kept in hot places such as the trunk or glove compartment of a car, or very cold places such as the freezer.

When traveling, be sure to keep bottles protected (such as wrapping them in clothing) and accessible (such as keeping them in carry-on baggage during air travel). The following rules are recommended to ensure safety:

• Do not use regular insulin or Humalog if it becomes cloudy in appearance.
  
  
• Do not use NPH or Lente insulin if it becomes clumped or crystalized or if the bottle becomes frosty.
  
  
• When combining insulin, be sure to inject the insulin within five minutes of mixing.