The Joslin Book of Diabetes

Chapter 1

What Is Diabetes?

Anytime you want to learn about a medical problem, it's best to approach it in two steps. First, learn how the body functions normally. Then focus on what happens when something goes wrong. This is the best way to learn about diabetes, too. First, you need to understand how the body normally produces energy. You should then focus on how a breakdown in this process leads to the two major types of diabetes -- either your body can't make any or enough insulin, or it can't properly use the insulin it produces.

How the Body Normally Produces Energy

Quite simply, you can't live without food. The body needs food to nourish itself and sustain life. Food is both "fuel" and "building material." It produces energy, builds and repairs body tissue, and regulates body functions. But before food is used by the cells, it's put through some biological paces. First, your body must break down the food you eat into its basic ingredients, or nutrients: These nutrients fall into three major categories -- carbohydrates, proteins, and fats.

Carbohydrates are found in most foods. Often called "starches" and "sugars," they are found in bread, pasta, fruits, and vegetables. Proteins are found in meats, milk, and fish. Fats are found in such foods as vegetable oils, meat, cheese, and other dairy products. All these nutrients are digested, or broken down, in the stomach and intestines. Carbohydrates are broken down into a simple sugar called glucose, which passes through the wall of the intestines into your bloodstream. This is the form of sugar that is often called "blood glucose" or, more simply, just "blood sugar." Diabetes is a disorder in the way the body uses blood sugar, or glucose.

The Role of Insulin

Once glucose gets into your bloodstream, it circulates to the body's cells to provide them energy. But glucose can't simply flow into the cells. All cells are enclosed by a thin wall called a membrane, and something has to tell your cells that glucose is waiting outside. That something is insulin. It attaches on the outside of the cells to special sites called insulin receptors -- much like a key that fits into a lock. Insulin is the "key" that unlocks the cells, allowing glucose to enter. Once inside, the glucose is metabolized, or "burned," by the cells for energy.

Exactly what kind of substance is insulin? It is a hormone -- a chemical messenger made in one part of the body to transmit "information" through your bloodstream to cells in another part of the body. Your body produces many types of hormones. Insulin is a specific kind of hormone made in the organ called the pancreas.

The Pancreas

The pancreas is a small gland situated below and behind the stomach. In an adult, it weighs less than half a pound. The pancreas is shaped like a long cone lying on its side, with the end tapering off into a "tail." Within this tail are tiny bits of tissue called islets of Langerhans.

A normal pancreas has about 100,000 islets of Langerhans. But these islets are actually clusters of various types of cells. The most important are the beta cells -- the tiny "factories" that make insulin. The beta cells also serve as "warehouses," storing insulin until it's needed by the body.

In addition to producing insulin, the pancreas has other important duties. Some cells produce hormones that are quite different from insulin, such as glucagon. This hormone actually raises the blood sugar -- just the opposite function of insulin. The balancing act between insulin and glucagon helps keep blood sugar in the normal range, approximately 60-140 milligrams (mg) of sugar per deciliter (dl) of blood. Other cells in the pancreas produce substances called enzymes, which help in digestion by splitting foodstuffs into simpler substances, which can then be absorbed through the intestine into the bloodstream.

How Insulin Works

During normal digestion, enzymes in the stomach and intestines act upon the nutrients (carbohydrates, proteins, and fats), splitting them into simple substances, which enter the bloodstream in the following forms:

* Carbohydrates are converted into glucose, which is metabolized, or "burned," for energy.

* Proteins are converted into amino acids, which provide the basic building blocks for bone, muscle, and other tissues. Proteins also can be burned for energy.

* Fats become fatty acids, which are burned for energy or stored as body fat for later use. However, fat is burned differently from glucose, producing substances called ketones.

Insulin plays a role in the burning and storage of all these nutrients. In diabetes, however, its main role relates to the action of glucose, the simplified form of carbohydrates. The whole process works like a dietary drama. The key actors are the beta cells, which make and store insulin. When they sense the level of glucose rising in the blood, they respond by releasing just the right amount of insulin into the bloodstream.

At first, the beta cells release the insulin held in storage. But what if the body needs even more? This often happens right after a meal, and as the blood glucose levels increase, a second stage begins. The "control centers" of the beta cells trigger them to make more insulin. When functioning normally, the beta cells release just enough insulin to maintain the level of glucose in the blood within the normal range of 60-140 mg/dl, and once in the bloodstream, the insulin enables the glucose to enter your body's cells for energy.

Another process also occurs. Generally when you eat, you don't need to use all the glucose from your food immediately. The body takes some of the glucose and stores it for future needs. With insulin's help, the extra glucose is taken up by the liver cells and changed to a storage form called glycogen. Glycogen comes in handy when your body needs extra energy in a hurry, for instance, during exercise. At those times, your body rises to the occasion by quickly changing the stored glycogen back into glucose. In addition, this stored glucose takes care of your energy needs overnight, a time when you normally aren't eating. Insulin also helps convert some of the extra glucose into fat, which is stored in the body's fat cells.

What Goes Wrong in Diabetes?

Diabetes is caused by a breakdown in the normal processes described above. A breakdown can occur in one of two ways: (1) the body produces little or no insulin; or (2) the insulin that the body produces can't link up with the body's cells. Type I diabetes is the result of the first defect; Type II is the result of the second. It is important to note, however, that there are many similarities between Type I and Type II diabetes, and that some people display characteristics of both types.

Type I: Insulin-Dependent Diabetes

Of all people with diabetes, about 5-10 percent have Type I, which develops most often in children and young adults. That's why it was once called "juvenile-onset" diabetes. However, this type of diabetes can occur in people of any age.

The Problem. Type I diabetes occurs when the pancreas produces very little, if any, insulin. In short, the beta cells do not function. People with this type of diabetes are insulin-dependent. They must have daily doses of insulin from an outside source to function and survive. Insulin must be provided by injection with a syringe ("a shot"). It cannot be taken by mouth because the stomach acids make insulin ineffective.

The Symptoms. By understanding what happens when the body lacks insulin, you can understand the various symptoms of diabetes -- the outward signs that something is wrong.

* Lack of energy. This symptom occurs because your body has no insulin to enable your cells to change blood sugar into energy. Without energy, you feel tired.

* Constant hunger. When you are unable to get energy from the sugar in your blood, your body sends out hunger signals for more food. Of course, a lack of sugar isn't the real problem. The problem is that your body can't use the sugar already there.

* Weight loss. This symptom often occurs because the body, unable to use sugar in the blood as a source of energy, turns to its reserve fat supplies for energy. As fat is used up, you lose weight.

* Frequent urination and excessive thirst. These symptoms are caused by a condition called hyperglycemia, or high blood sugar. In all people, whether they have diabetes or not, the blood circulates through the kidneys. These organs remove waste materials from the blood which are then expelled in urine. The kidneys also act like a "dam" to retain and recycle important nutrients such as sugar, sending them back into the blood. In diabetes, blood sugar rises to excessively high levels, which overwhelms the kidneys. They can't send all the sugar back into circulation, and it spills over the "dam" into the urine. Something else goes with it -- water, which results in large volumes of urine. And as you lose fluids, you get extra thirsty, your body's signal to take in more fluids.

* Blurred vision. If you have high blood pressure, sugar can build up in the fluids of your eyes. The excess sugar draws water with it, causing the eye's outer lens to swell, which distorts your vision. However, once you begin your diabetes treatment and your blood sugar gets back to more normal levels, your vision will clear.

* Other symptoms. Perhaps you had other symptoms of diabetes before your problem was identified. You may have experienced nausea, vomiting, abdominal pain, weakness, or rapid shallow breathing. It's even possible you experienced a diabetic coma prior to getting medical assistance. All of these symptoms can occur when your body uses stored fat instead of glucose as an alternative source of energy.

Whenever a person goes for long periods without food, it's natural for the body to use stored fat for energy. As the body uses the fat, acid substances called ketones are formed and accumulate in the blood. Under normal circumstances, the level of ketones is low and harmless.

In diabetes, when there is not enough insulin to allow glucose to be used for energy, the body must rely exclusively on fat for its energy needs. As a result, high levels of both glucose and ketones accumulate in the blood and spill into the urine. This process is called ketosis and can lead to a serious problem called diabetic ketoacidosis, in which the acid in the blood is excessively high. Ketoacidosis can cause all of the symptoms described above and may even lead to diabetic coma, a life-threatening condition.

The Cause. Type I diabetes results from the destruction of the beta cells of the pancreas. Why does this occur? Research during the past decade has brought us closer to an answer. As yet, scientists don't know for sure, but they believe that most cases of Type I diabetes are caused when something has gone wrong in the body's immune system. The main job of your immune system is to fight diseases by producing antibodies, substances that eliminate foreign invaders, such as bacteria and viruses. In certain cases, however, the immune system goes haywire and destroys the body's own cells. Researchers believe that this is what happens in most cases of Type I diabetes. By mistake, the body destroys the beta cells of the pancreas, the very cells it needs to produce insulin.

Again, scientists don't know why this happens. But heredity probably plays a role. In other words, there is a tendency for the problem to occur more frequently in certain families. Studies show that if one parent has Type I diabetes, a child has a 5 to 10 percent chance of developing the same condition. The risk rises to 20 percent when both parents have Type I diabetes.

New tests now make it possible to detect faulty immune antibodies in the blood -- years before a person shows any of the common symptoms of diabetes. In adults, the destructive antibodies may be in the blood five or more years before symptoms appear. This suggests that the destruction of beta cells doesn't occur abruptly. Instead, it is a gradual process, taking place during what is called the "prediabetic stage." Nationwide research studies are now being undertaken to look for ways to halt the destruction of the beta cells during this stage. For this reason, people with an immediate relative with Type I diabetes are being encouraged to be tested for the presence of faulty antibodies that may lead to diabetes. If they are detected, perhaps these people can be given a treatment that would prevent further destruction of the beta cells. Insulin, itself, is one possible treatment being studied to prevent diabetes. You can contact Joslin Diabetes Center for the latest information on these prevention studies, and for information on how to be screened.

Type II: Non-Insulin-Dependent Diabetes

Type II diabetes is the most common kind of diabetes, accounting for about 90 percent of all cases. Until recently, Type II diabetes was referred to as "maturity-onset" diabetes because it occurs most often in mature adults, age 40 or older.

The Problem. If you have Type II diabetes, your beta cells can still produce insulin. But unfortunately, there isn't enough to meet the present needs of your body. Compounding the problem, your body's cells can't respond properly to the available insulin to let glucose inside. People with Type II diabetes usually do not depend on insulin injections to survive. That's why it is now often called non-insulin-dependent diabetes. However, it's important to note that some people with this type of diabetes may still need daily injections of insulin to maintain good health.

The Symptoms. A number of symptoms are associated with Type II diabetes, which, in many ways, are similar to those found with Type I diabetes.

* Lack of energy. When sugar can't enter your body's cells, they can't use it for energy, and this can lead to fatigue. In short, you're plumb out of energy.

* Increased hunger. Unable to use the available sugar for energy, the body signals for more food -- what you perceive as hunger pangs.

* Weight loss. Unable to use the sugar in the bloodstream, the body gets its energy from stored fat. As these fat stores are used up, you lose weight.
* Hyperglycemia. If the body is unable to use the glucose in the bloodstream, it starts to "back up." When it accumulates to a certain point, it creates the condition called hyperglycemia, or high blood sugar.

* Blurred vision. High blood sugar can lead to a buildup of sugar in the eye fluids. The excess sugar draws in water, causing the eye's outer lens to change shape, which distorts your vision.

* Frequent urination and excessive thirst. The circulating blood travels through the kidneys, where normally the unused sugar is recycled for later use or for storage. However, when the levels of blood sugar are unduly high, the kidneys are unable to recycle it all and the excess sugar spills into the urine, drawing additional water with it and resulting in large volumes of urine. This accounts for frequent urination, and depleted of its normal amount of fluids, your body sends out thirst signals, telling you to drink more fluids.

* Irritation and damage to the nerves. Also caused by high blood sugar, an early sign o...