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Diabetes Mellitus: Overview and Risk Factors

The term diabetes mellitus refers to a group of diseases that result in higher than normal amounts of sugar (glucose) in the bloodstream.

Diabetes occurs as a result of deficiency or insufficient action of insulin, a hormone that helps glucose to enter cells. In type 1 diabetes, the insulin–producing cells of the pancreas are destroyed, resulting in a complete absence of insulin. In type 2 diabetes, the pancreas is able to produce insulin, at least initially, but the cells of the body resist insulin’s action, causing the body to need to produce extra insulin in order to get glucose into cells. When the pancreas can no longer produce enough insulin to maintain normal blood glucose levels, diabetes is diagnosed.

Diabetes can result in many complications, including heart disease, eye problems, kidney failure, nerve symptoms, leg amputation, and others. See the Diabetes Complications chapter for more information on these.

There are three major types of diabetes mellitus:

  • Type 1 diabetes, accounting for approximately 5 to 10 percent of all cases, occurs as a result of destruction of the insulin–producing cells of the pancreas. Most cases begin in childhood with symptoms of unexplained weight loss, fatigue, excessive thirst and urination, and blurred vision. Less commonly, it can also be diagnosed in adults. Type 1 diabetes requires insulin treatment.
  • Type 2 diabetes, which accounts for roughly 90 percent of diabetes cases, is often associated with excess weight. Most cases occur in adults, but the occurrence is climbing rapidly in children, due to increasing rates of childhood obesity. Type 2 diabetes is often accompanied by hypertension and high cholesterol. Although some patients with type 2 diabetes require insulin injections, most are treated with oral medications. Symptoms tend to be much milder in type 2 than in type 1 when the disease first presents, but complications of type 2 diabetes are frequent and can be life–threatening.
  • Gestational diabetes mellitus accounts for about 2 percent of diabetes cases. As its name suggests, gestational diabetes first appears during pregnancy. Hormones secreted by the placenta–estrogen, progesterone, growth hormone, corticotrophin–releasing hormone, and prolactin–decrease the function of insulin, resulting in high blood sugar. Treatment with dietary changes and/or drugs (usually insulin) is essential to prevent fetal complications. Although blood sugar levels usually normalize after birth, many women with gestational diabetes eventually develop type 2 diabetes.

Risk Factors

Risk factors for type 1 diabetes include:

  • Family history: When a first–degree relative has diabetes, the risk of developing type 1 diabetes is about 10 to 15 percent. Many possible genes are under investigation.
  • Exposure to cow’s milk proteins: Consumption of cow’s milk in early childhood has been under investigation as a contributing factor.
  • Fetal or childhood viral infections
  • Birth weight greater than 9.9 pounds
  • Preeclampsia (high maternal blood pressure during mother’s pregnancy)
  • Being born to a mother older than 25

Risk factors for type 2 diabetes include:

  • Family history of type 2 diabetes in first– or second–degree relatives
  • Older age
  • Abdominal obesity
  • History of gestational diabetes
  • The presence of hypertension and high cholesterol
  • Race and Ethnicity: African–Americans, Latinos, American Indian/Alaska Natives, and Asians and Pacific Islanders have a greater risk.

Risk factors for gestational diabetes are listed below. In addition, individuals of Asian, African, Native–American, and Hispanic ancestry have greater risk for gestational diabetes than non–Hispanic whites. The risk factors for gestational diabetes overlap with type 2 diabetes.

  • Family history of type 2 diabetes in a first–degree relative
  • History of high blood sugar
  • Steroid use during pregnancy
  • Polycystic ovarian syndrome
  • Age greater than 25 years
  • A pre–pregnancy weight at least 10 percent above ideal body weight
  • Previous child with birth weight greater than 9 pounds
  • Maternal birth weight greater than 9 pounds or less than 6 pounds


Diabetes Mellitus: Diagnosis and Treatment >>