Type 2 Diabetes
About 90% of diabetic Americans have type 2 diabetes. The prevalence of type 2 diabetes is higher in African Americans, Native Americans, Hispanics, and Pacific Islanders than it is in Caucasians. Most type 2 diabetes patients are overweight, and most are diagnosed as adults. The genetic influence in type 2 diabetes is greater than that seen with type 1. While concordance rates between monozygous twins for type 1 diabetes are about 30 to 50%, the rate is approximately 90% for type 2 diabetes. Although the genetic predisposition to type 2 diabetes is strong, no single genetic defect has been found. In addition to genetic influences, acquired risk factors for type 2 diabetes include obesity, advancing age, and an inactive lifestyle.
The underlying pathophysiologic defect in type 2 diabetes does not involve autoimmune beta-cell destruction. Rather, type 2 diabetes is characterized by the following three disorders: (1) peripheral resistance to insulin, especially in muscle cells; (2) increased production of glucose by the liver; and, (3) altered pancreatic insulin secretion. Increased tissue resistance to insulin generally occurs first and is eventually followed by impaired insulin secretion. The pancreas produces insulin, yet insulin resistance prevents its proper use at the cellular level. Glucose cannot enter target cells and accumulates in the bloodstream, resulting in hyperglycemia. The high blood glucose levels often stimulate an increase in insulin production by the pancreas; thus, type 2 diabetic individuals often have excessive insulin production (hyperinsulinemia). Over the years, pancreatic insulin production usually decreases to below normal levels. In addition to hyperglycemia, type 2 diabetic patients often have a group of disorders that has been called "insulin resistance syndrome" or syndrome X.
Obesity contributes greatly to insulin resistance, even in the absence of diabetes. In fact, weight loss is a cornerstone of therapy for obese type 2 diabetic patients. Insulin resistance generally decreases with weight loss. Obesity also may explain the dramatic increase in the incidence of type 2 diabetes among young individuals in the United States in the past 10 to 20 years. Once considered a disease of adults, type 2 diabetes has increased among America's youth in direct