Diabetes Mellitus, disease in which the pancreas produces little or no insulin, a hormone that helps the body’s tissues absorb glucose (sugar) so it can be used as a source of energy. The condition may also develop if muscle, fat, and liver cells respond poorly to insulin. In people with diabetes, glucose levels build up in the blood and urine, causing excessive urination, thirst, hunger, and problems with fat and protein metabolism. Diabetes mellitus differs from the less common diabetes insipidus, which is caused by lack of the hormone vasopressin that controls the amount of urine secreted.
Diabetes is most common in adults over 45 years of age; in people who are overweight or physically inactive; in individuals who have an immediate family member with diabetes; and in people of African, Hispanic, and Native American descent. The highest rate of diabetes in the world occurs in Native Americans. More women than men have been diagnosed with the disease.
In diabetes mellitus low insulin levels prevent cells from absorbing glucose. As a result, glucose builds up in the blood. When glucose-laden blood passes through the kidneys, the organs that remove blood impurities, the kidneys cannot absorb all of the excess glucose. This excess glucose spills into the urine, accompanied by water and electrolytes—ions required by cells to regulate the electric charge and flow of water molecules across the cell membrane. This causes frequent urination to get rid of the additional water drawn into the urine; excessive thirst to trigger replacement of lost water; and hunger to replace the glucose lost in urination. Additional symptoms may include blurred vision, dramatic weight loss, irritability, weakness and fatigue, and nausea and vomiting.
Diabetes is classified into two types. In Type 1 diabetes, formerly called insulin-dependent diabetes mellitus (IDDM) and juvenile-onset diabetes, the body does not produce insulin or produces it only in very small quantities. Symptoms usually appear suddenly, typically in individuals under 20 years of age. Most cases occur around puberty—around age 10 to 12 in girls and age 12 to 14 in boys.
Type 1 diabetes is considered an autoimmune disease because the immune system (system of organs, tissues, and cells that rid the body of disease-causing organisms or substances) attacks and destroys insulin-producing cells, known as beta cells, in the pancreas. Scientists believe that a combination of genetic and environmental factors may somehow trigger the immune system to destroy these cells. Untreated Type 1 diabetes affects the metabolism of fat. Because the body cannot convert glucose into energy, it begins to break down stored fat for fuel. This produces increasing amounts of acidic compounds in the blood called ketone bodies, which interfere with cellular respiration, the energy-producing process in cells
In Type 2 diabetes, formerly known as non-insulin-dependent diabetes mellitus (NIDDM) and adult-onset diabetes, the body’s delicate balance between insulin production and the ability of cells to use insulin goes awry. Symptoms characteristic of Type 2 diabetes include those found in Type 1 diabetes, as well as repeated infections or skin sores that heal slowly or not at all, generalized tiredness, and tingling or numbness in the hands or feet. The onset of Type 2 diabetes usually occurs after the age of 45, although the incidence of the disease in younger people is growing rapidly. Because symptoms develop slowly, individuals with the disease may not immediately recognize that they are sick. A number of genes work together to cause Type 2 diabetes. In addition, scientists believe that there is a strong relationship between obesity and Type 2 diabetes. About 80 percent of diabetics with this form of the disease are significantly overweight.
Type 1 diabetes can result in diabetic coma (a state of unconsciousness caused by extremely high levels of glucose in the blood) or death. In both Type 1 and Type 2 diabetes, complications may include blindness, kidney failure, and heart disease. Diabetes can cause tiny blood vessels to become blocked; when this occurs in blood vessels of the eye, it can result in retinopathy (the breakdown of the lining at the back of the eye), causing blindness. Diabetes mellitus is the leading cause of new cases of blindness in people aged 20 to 74. When diabetes affects the kidney it is called nephropathy (the inability of the kidney to properly filter body toxins). About 40 percent of new cases of end-stage renal disease (kidney failure) are caused by diabetes mellitus. Blockages of large blood vessels in diabetics can lead to many cardiovascular problems, including high blood pressure, heart attack, and stroke. Although these conditions also occur in nondiabetic individuals, people with diabetes are two to four times more likely to develop cardiovascular disorders.
Diabetes mellitus may also cause loss of feeling, particularly in the lower legs. This numbness may prevent a person from feeling the pain or irritation of a break in the skin or of foot infection until after complications have developed, possibly necessitating amputation of the foot or leg. Burning pain, sensitivity to touch, and coldness of the foot, conditions collectively known as neuropathy, can also occur. Other complications include higher-risk pregnancies in diabetic women and a greater occurrence of dental disease.
Diagnosis and Treatment
Diabetes is detected by measuring the amount of glucose in the blood after an individual has fasted (abstained from food) for about eight hours. In some cases, physicians diagnose diabetes by administering an oral glucose tolerance test, which measures glucose levels before and after a specific amount of sugar has been ingested. Another test being developed for Type 1 diabetes looks for specific antibodies (proteins of the immune system that attack foreign substances) present only in persons with diabetes. This test may detect Type 1 diabetes at an early stage, reducing the risk of complications from the disease.
Once diabetes is diagnosed, treatment consists of controlling the amount of glucose in the blood and preventing complications. Depending on the type of diabetes, this can be accomplished through regular physical exercise, a carefully controlled diet, and medication.
Individuals with Type 1 diabetes require insulin injections, often two to four times a day, to provide the body with the insulin it does not produce. The amount of insulin needed varies from person to person and may be influenced by factors such as a person’s level of physical activity, diet, and the presence of other health disorders. Typically, individuals with Type 1 diabetes use a meter several times a day to measure the level of glucose in a drop of their blood obtained by pricking a fingertip. They can then adjust the amount of insulin injected, physical exercise, or food intake to maintain the blood sugar at a normal level. People with Type 1 diabetes must carefully control their diets by distributing meals and snacks throughout the day so as not to overwhelm the ability of the insulin supply to help cells absorb glucose. They also need to eat foods that contain complex sugars, which break down slowly and cause a slower rise in blood sugar levels.
For persons with Type 2 diabetes, treatment begins with diet control, exercise, and weight reduction, although over time this treatment may not be adequate. People with Type 2 diabetes typically work with nutritionists to formulate a diet plan that regulates blood sugar levels so that they do not rise too swiftly after a meal. A recommended meal is usually low in fat (30 percent or less of total calories), provides moderate protein (10 to 20 percent of total calories), and contains a variety of carbohydrates, such as beans, vegetables, and grains. Regular exercise helps body cells absorb glucose—even ten minutes of exercise a day can be effective. Diet control and exercise may also play a role in weight reduction, which appears to partially reverse the body’s inability to use insulin.
For some people with Type 2 diabetes, diet, exercise, and weight reduction alone may work initially, but eventually this regimen does not help control high blood sugar levels. In these cases, oral medication may be prescribed. If oral medications are ineffective, a person with Type 2 diabetes may need insulin injections or a combination of oral medication and insulin injections. About 49 percent of individuals with Type 2 diabetes require oral medications, 40 percent require insulin injections or a combination of insulin injections and oral medications, and 10 percent use diet and exercise alone.
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