Insulin is an essential hormone produced by specialized cells in the pancreas. It plays a crucial role in the metabolism of fats and carbohydrates in the body, and is released into the circulation after eating. As food is broken down through digestive processes into simple components, such as fatty acids, proteins, and glucose, these nutrients pass into the bloodstream. Insulin works to “escort” glucose into the body’s muscle, liver, and fat cells, where glucose is burned for immediate energy, or stored for future use as a substance called glycogen. While our bodies need adequate blood glucose levels to function properly, too much sugar in the blood can also be harmful.
Type 2 diabetes begins with a condition called insulin resistance, in which the cells no longer respond efficiently to the presence of insulin. At first the body reacts by producing more insulin. In this phase it’s still possible to reverse the course of the disease by following an improved diet (more fiber and plant foods; fewer calories and fats), and committing to regular exercise. Patients with insulin resistance may also be prescribed medications that can help boost their cells’ responsiveness to insulin. In the absence of weight loss and improved fitness, which help control blood sugar levels, the beta cells (insulin producing cells) of the pancreas eventually “burn out.” If this occurs, the patient will need “man-made” insulin to survive: He or she becomes an insulin-dependent diabetic.
At this stage, without supplemental insulin administered on a regular basis, the patient’s blood sugar levels will skyrocket after eating. Untreated, the condition can be fatal. Fortunately, doctors can prescribe supplemental insulin, which may be administered through a variety of routes. The most common is injectable insulin. More than 40 percent of people with type 2 diabetes will eventually require insulin to control their disease.
Insulin is a peptide hormone, constructed from 51 amino acids. Although this vital hormone is found throughout the animal kingdom, its structure varies slightly among species. Insulin from pigs is closest in structure to that of humans, differing by just one amino acid—which is why pig insulin is often used as a replacement for human insulin.
Ordinarily, blood insulin levels rise and fall gently in response to glucose and other nutrients entering the bloodstream. They oscillate, rising and falling in a rhythm that evidently helps maintain muscle and liver cells’ responsiveness to insulin. This natural oscillation should be emulated as much as possible when administering supplemental insulin.
Types of Insulin
Four different types of insulin are on the market, categorized according to how quickly they take effect (onset of action) and how long they remain active in the body (duration). Categories include rapid-, short-, intermediate- and long-acting insulin. Some injectable insulin types (so-called biphasic insulin) feature a mixture of two types, such as 70 percent intermediate-acting and 30 percent rapid-acting. Injectable insulin comes in small rubber-stoppered glass bottles that contain multiple doses, which must be carefully measured with each injection.
This type is administered beneath the skin (subcutaneous injection) with a disposable needle. Another option is the insulin “pen,” a convenient device that uses single disposable cartridges of insulin to deliver a metered dose beneath the skin. Still other options include the jet injector, which sprays the hormone into the skin, and the insulin pump, which patients wear continuously. Attempts by drug manufacturers to develop insulin that is inhaled have largely failed, either in the clinical trial phase, or due to rejection by the marketplace. Future goals include the perfection of islet cell transplantation, which, if effective, would help patients may regain the ability to produce insulin “naturally.”
Side Effects of Insulin Therapy
Potential side effects of insulin therapy include a condition called insulin shock, or severe hypoglycemia (low blood sugar), in which glucose levels drop below 70 mg/dl. In such cases, it’s important to consume some replacement sugar immediately, in the form of glucose tablets, honey, fruit juice, etc.
Rapid-onset insulin can cause a blood-sugar drop in as few as ten minutes. Symptoms may include:
- rapid heartbeat
- blurred vision
In extreme cases, (insulin shock) severe hypoglycemia may cause fainting, a seizure, or even coma. Factors such as failing to eat before taking insulin, drinking alcohol, exercising more vigorously (or at a different time) than usual, or administering an injection at the wrong time may all play a role in bringing about such a hypoglycemic episode.