Diabetes mellitus is a common metabolic disorder resulting from defects in insulin action, insulin production, or both. Insulin, a hormone secreted by the pancreas, helps the body use and store glucose produced during the digestion of food. Characterized by hyperglycemia , symptoms of diabetes include frequent urination, increased thirst, dehydration , weight loss, blurred vision, fatigue , and, occasionally, coma. Uncontrolled hyperglycemia over time damages the eyes, nerves, blood vessels, kidneys, and heart, causing organ dysfunction and failure. A number of risk factors are attributed to the incidence of diabetes, including family history, age, ethnicity, and social group characteristics, as well as behavioral , lifestyle, psychological , and clinical factors.
The World Health Organization estimates that 150 million people had diabetes worldwide in 2002. This number is projected to double by the year 2025. Much of this increase will occur in developing countries and will be due to population growth, aging, unhealthful diets, obesity , and sedentary lifestyles. In the United States, diabetes is the sixth leading cause of death. While 6.2 percent of the population has diabetes, an estimated 5.9 million people are unaware they have the disease. In addition, about 19 percent of all deaths in the United States for those age twenty-five and older are due to diabetes-related complications.
The prevalence of diabetes varies by age, gender, race, and ethnicity. In the United States, about 0.19 percent of the population less than twenty years of age (151,000 people) have diabetes, versus 8.6 percent of the population twenty years of age and older. In addition, adults sixty-five and older account for 40 percent of those with diabetes, despite composing only 12 percent of the population. Considerable variations also exist in the prevalence of diabetes among various racial and ethnic groups. For example, 7.8 percent of non-Hispanic whites, 13 percent of non-Hispanic blacks, 10.2 percent of Hispanic/Latino Americans, and 15.1 percent of American Indians and Alaskan Natives have diabetes. Among Asian Americans and Pacific
Types of Diabetes
Diabetes mellitus is classified into four categories: type 1, type 2, gestational diabetes, and other. In type 1 diabetes, specialized cells in the pancreas are destroyed, leading to a deficiency in insulin production. Type 1 diabetes frequently develops over the course of a few days or weeks. Over 95 percent of people with type 1 diabetes are diagnosed before the age of twenty-five. Estimates show 5.3 million people worldwide live with type 1 diabetes. Although the diagnosis of type 1 diabetes occurs equally among men and women, an increased prevalence exists in the white population. Type 1 diabetes in Asian children is relatively rare.
Family history, diet , and environmental factors are risk factors for type 1 diabetes. Studies have found an increased risk in children whose parents have type 1 diabetes, and this risk increases with maternal age. Environmental factors such as viral infections, toxins , and exposure to cow's milk are being contested as causing or modifying the development of type 1 diabetes.
Type 2 diabetes is characterized by insulin resistance and/or decreased insulin secretion. It is the most common form of diabetes mellitus, accounting for 90 to 95 percent of all diabetes cases worldwide. Risk factors for type 2 diabetes include family history, increasing age, obesity, physical inactivity, ethnicity, and a history of gestational diabetes. Although type 2
Genetics and environmental factors are the main contributors to type 2 diabetes. Physical inactivity and adoption of a Western lifestyle (particularly choosing foods with more animal protein , animal fats, and processed carbohydrates ), especially in indigenous people in North American and within ethnic groups and migrants, have contributed to weight gain and obesity. In fact, obesity levels increased by 74 percent between 1991 and 2003. Increased body fat and abdominal obesity are associated with insulin resistance, a precursor to diabetes. Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) are two prediabetic conditions associated with insulin resistance. In these conditions, the blood glucose concentration is above the normal range, but below levels required to diagnose diabetes. Subjects with IGT and/or IFG are at substantially higher risk of developing diabetes and cardiovascular disease than those with normal glucose tolerance. The conversion of individuals with IGT to type 2 diabetes varies with ethnicity, anthropometric measures related to obesity, fasting blood glucose (a measurement of blood glucose values after not eating for 12 to 14 hours), and the two-hour post-glucose load level (a measurement of blood glucose taken exactly two hours after eating). In addition to IGT and IFG, higher than normal levels of fasting insulin, called hyperinsulinemia, are associated with an increased risk of developing type 2 diabetes. Insulin levels are higher in African Americans than in whites, particularly African-American women, indicating their greater predisposition for developing type 2 diabetes.
The complexity of inheritance and interaction with the environment makes identification of genes involved with type 2 diabetes difficult. Only a small percentage (2–5%) of diabetes cases can be explained by single gene defects and are usually atypical cases. However, a "thrifty gene," although not yet identified, is considered predictive of weight gain and the development of type 2 diabetes. Thrifty-gene theory suggests that indigenous people who experienced alternating periods of feast and famine gradually developed a way to store fat more efficiently during periods of plenty to better survive famines. Regardless of the thrifty gene, the contribution of genetic mutations in the development of type 2 diabetes has not been established, due to the number of genes that may be involved.
Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance with onset or first recognition during pregnancy. This definition applies regardless of whether insulin or diet modification is used for treatment, and whether or not the condition persists after pregnancy. GDM affects up to 14 percent of the pregnant population—approximately 135,000 women per year in United States. GDM complicates about 4 percent of all pregnancies in the U.S. Women at greatest risk for developing GDM are obese , older than twenty-five years of age, have a previous history of abnormal glucose control, have first-degree relatives with diabetes, or are members of ethnic groups with a high prevalence of diabetes. Infants of a woman with GDM are at a higher risk of developing obesity, impaired glucose tolerance, or diabetes at an early age. After a pregnancy with GDM, the mother has an increased risk of developing type 2 diabetes.
Other forms of diabetes are associated with genetic defects in the specialized cells of the pancreas, drug or chemical use, infections, or other diseases. The most notable of the genetically linked diabetes is maturity onset diabetes of the young (MODY). Characterized by the onset of hyperglycemia before the age of twenty-five, insulin secretion is impaired while minimal or no defects exist in insulin action. Drugs , infections, and diseases cause diabetes by damaging the pancreas and/or impairing insulin action or secretion.
People with diabetes are at increased risk for serious long-term complications. Hyperglycemia, as measured by fasting plasma glucose concentration or glycosylated hemoglobin (HbA1c), causes structural and functional changes in the retina, nerves, kidneys, and blood vessels. This damage can lead to blindness, numbness, reduced circulation, amputations, kidney disease, and cardiovascular disease. Type 1 diabetes is more likely to lead to kidney failure. About 40 percent of people with type 1 diabetes develop severe kidney disease and kidney failure by the age of fifty. Nevertheless, between 1993 and 1997, more than 100,000 people in the United States were treated for kidney failure caused by type 2 diabetes.
African Americans experience higher rates of diabetes-related complications such as eye disease, kidney failure, and amputations. They also experience greater disability from these complications. The frequency of diabetic retinopathy (disease of the small blood vessels in the retina causing deterioration of eyesight) is 40 to 50 percent higher in African Americans than in white Americans. In addition, the rate of diabetic retinopathy among Mexican Americans is more than twice that of non-Hispanic white Americans. Furthermore, African Americans with diabetes are much more likely to undergo a lower-extremity amputation than white or Hispanic Americans with diabetes. Little is known about these complications in Asian and Pacific Islander-Americans.
Diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemia state (HHS) are serious diabetic emergencies and the most frequent cause of mortality. Both DKA and HHS result from an insulin deficiency and an increase in counter-regulatory hormones (a.k.a. hyperglycemia). Hyperglycemia leads to glycosuria (glucose in the urine), increased urine output, and dehydration. Because the glucose is excreted in the urine, the body becomes starved for energy . At this point, the body either continues to excrete glucose in the urine making the hyperglycemia worse (HHS), or the body begins to break down triglycerides causing the release of ketones (by-products of fat breakdown) into the urine and bloodstream (DKA). The mortality rate of patients with DKA is less than 5 percent while the mortality rate of HHS patients is about 15 percent. Infection (urinary tract infections and pneumonia account for 30 to 50 percent of cases), omission of insulin, and increased amounts of counter-regulatory hormones contribute to DKA and HHS. Type 1 and type 2 diabetic patients may experience DKA and HHS. However, DKA is more common in type 1 diabetic patients, while HHS is more common in type 2 diabetic patients. Treatment of DKA and HHS involves correction of dehydration, hyperglycemia, ketoacidosis, and electrolyte deficits and imbalances.
Treatment for Diabetes
Treatment for diabetes involves following a regimen of diet, exercise, self-monitoring of blood glucose, and taking medication or insulin injections. Although type 1 diabetes is primarily managed with daily insulin injections, type 2 diabetes can be controlled with diet and exercise. However, when diet and exercise fail, medication is added to stimulate the production of insulin, reduce insulin resistance, decrease the liver's output of glucose, or slow absorption of carbohydrate from the gastrointestinal tract. When medication fails, insulin is required.
Following the diagnosis of diabetes, a diabetic patient undergoes medical nutrition therapy. In other words, a registered dietician performs a nutritional assessment to evaluate the diabetic patient's food intake, metabolic status, lifestyle, and readiness to make changes, along with providing dietary instruction and goal setting. The assessment is individualized and takes into account cultural, lifestyle, and financial considerations. The goals of medical nutrition therapy are to attain appropriate blood glucose, lipid, cholesterol , and triglyceride levels, which are critical to preventing the chronic complications associated with diabetes. For meal planning, the diabetic exchange system provides a quick method for estimating and maintaining the proper balance of carbohydrates, fats, proteins, and calories . In the exchange system, foods are categorized into groups, with each group having food with similar amounts of carbohydrate, protein, fat, and calories. Based on the individual's diabetes treatment plan and goals, any food on the list can be exchanged with another food within the same group.
Exercise and blood glucose monitoring are also critical components of a diabetic patient's self-management. Exercise improves blood glucose control, increases sensitivity to insulin, reduces cardiovascular risk factors, contributes to weight loss, and improves well-being. Exercise further contributes to a reduction in the risk factors for diabetes-related complications. Daily self-monitoring of blood glucose levels allows diabetic patients to evaluate and make adjustments in diet, exercise, and medications. Self-monitoring also assists in preventing hypoglycemic episodes.
Diabetes, Heart Disease, and Stroke
Many people with diabetes are not aware that they are at particularly high risk for heart disease and stroke, which can result from the poor blood flow that is a symptom of diabetes. In addition, people with type 2 diabetes have higher rates of hypertension and obesity, which are additional risk factors. Diabetics are two to four times more likely to have a heart attack than nondiabetics, and at least 65 percent of people with diabetes die from heart attack or stroke. While deaths from heart disease have been declining overall, deaths from heart disease among women with diabetes have increased, and deaths from heart disease among men with diabetes have not declined nearly as rapidly as they have among the general male population. The National Diabetes Education Program has launched a campaign to bring the problem to public attention. Patients are advised to work with medical personnel to control their glucose level, blood pressure, and cholesterol level and, of course, to avoid smoking.
Diabetes mellitus is a chronic and debilitating disease. Attributed to genetics, physical inactivity, obesity, ethnicity, and a number of environmental factors, diabetes requires lifestyle changes and medication adherence in order to control blood glucose levels. Due to the damage caused by hyperglycemia, diabetic patients also experience a number of complications related to the disease. With good self-management practices, however, individuals with diabetes can live a long and productive life.
American Diabetes Association (2003) "Gestational Diabetes Mellitus." Diabetes Care 26(1):S103–S105.
American Diabetes Association (2003) "Hyperglycemic Crises in Patients with Diabetes Mellitus." Diabetes Care 26(1):S109–S117.
American Diabetes Association (2003) "Physical Activity/Exercise and Diabetes Mellitus." Diabetes Care 26(1):S73–77.
American Diabetes Association (2003) "Standards of Medical Care for Patients with Diabetes Mellitus." Diabetes Care 26(1):S33–S50.
Atkinson, Mark A., and Eisenbarth, George S. (2001). "Type 1 Diabetes: New Perspectives on Disease Pathogenesis and Treatment." Lancet 358:221–229.
Black, Sandra A. (2002). "Diabetes, Diversity, and Disparity: What Do We Do with the Evidence?" American Journal of Public Health 92(4):543–548.
Chiasson, Jean-Louis; Aris-Jilwan, Nahla; Belanger, Raphael; Bertrand, Sylvie; Beauregard, Hugues; Ekoe, Jean-Marie; Fournier, Helene; and Havrankova, Jana (2003). "Diagnosis and Treatment of Diabetic Ketoacidosis and the Hyperglycemic Hyperosmolar State." Canadian Medical Association Journal 168(7):859–866.
Green, Anders (1996). "Prevention of IDDM: The Genetic Epidemiologic Perspective." Diabetes Research and Clinical Practice 34:S101–S1006.
Mandrup-Paulson, Thomas (1998). "Recent Advances: Diabetes." British Medical Journal 316(18):1221–1225.
Mokdad, Ali H.; Ford, Earl S.; Bowman, Barbara A.; Dietz, William, H.; Vinicor, Frank; Bales, Virginia, S.; and Marks, James S. (2003). "Prevalence of Obesity, Diabetes, and Obesity-Related Health Risk Factors, 2001." Journal of the American Medical Association 289(1):76–79.
Jovanovic, Lois, and Pettitt, David J. (2001). "Gestational Diabetes Mellitus." Journal of the American Medical Association 283(20):2516–2518.
Kitabchi, Abbas E.; Umpierrez, Guillermo E.; Murphy, Mary Beth; Barrett, Eugene J.; Kreisberg, Robert A.; Malone, John I.; and Wall, Barry M. (2001). "Management of Hyperglycemic Crises in Patients with Diabetes." Diabetes Care 24(1):131–153.
Simpson, R. W.; Shaw, J. E.; and Zimmet, P. Z. (2003). "The Prevention of Type 2 Diabetes—Lifestyle Change or Pharmacotherapy? A Challenge for the 21st Century." Diabetes Research and Clinical Practice 59:165–180.
Yki-Jarvinen, Hannele (1998). "Toxicity of Hyperglycemia in Type 2 Diabetes." Diabetes/Metabolism Reviews 14:S45–S50.
American Diabetes Association. "Basic Diabetes Information." Available from <http://www.diabetes.org>
Centers for Disease Control and Prevention. "Diabetes Public Health Resource." Available from <http://www.cdc.gov/diabetes>
National Diabetes Information Clearinghouse (NDIC). "Diabetes." Available from <http://diabetes.niddk.nih.gov>
World Health Organization. "Fact Sheets: Diabetes Mellitus." Available from <http://www.who.int>