Diabetes Mellitus: Overview and Risk Factors

Diabetes mellitus (DM) includes a group of metabolic diseases characterized by hyperglycemia, which is attributable to insulin deficiency and/or insulin resistance. It leads to a wide range of complications and, when poorly controlled, can contribute to significant morbidity and mortality (see Diabetes Complications chapter). Three main types of diabetes are recognized:

Type 1 diabetes, accounting for approximately 5% to 10% of total cases, occurs after destruction of the insulin-producing beta-islet cells of the pancreas (usually through an autoimmune process). Most cases present in childhood with polyuria and polydipsia, unexplained weight loss, fatigue, and blurred vision. The condition can also be diagnosed in adults. Type 1 diabetes requires insulin treatment.

Type 2 diabetes, which accounts for more than 80% of diabetes cases, usually presents in adults after a long, asymptomatic course. About 85% of patients are centrally obese, and insulin resistance is typically present. Diabetes manifests when insulin production fails to keep pace with the body's increased need. Prevalence in children is climbing rapidly, due to increasing obesity. Type 2 diabetes is often accompanied by hypertension and lipid abnormalities and is part of the metabolic syndrome. Although symptoms upon initial presentation tend to be much milder in type 2 than in type 1 diabetes, complications are frequent and increase in prevalence over time if metabolic control is poor.

Gestational diabetes mellitus (GDM) accounts for about 2% of diabetes cases. As its name suggests, GDM first appears during pregnancy. Hormones secreted by the placenta--estrogen, progesterone, growth hormone, corticotrophin-releasing hormone, and prolactin--oppose insulin's function, and the pancreas struggles to produce enough insulin to compensate for the greater caloric intake during pregnancy. Treatment with dietary modification and/or drugs (usually insulin) is essential to prevent fetal complications. Although blood glucose levels usually normalize postpartum, many women with GDM 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% to15%. Many possible genes are under investigation.
• Exposure to bovine milk proteins. Consumption of cow's milk in early childhood has been under investigation as a contributing factor, although it has not yet been definitively established.
• Fetal or childhood Coxsackie virus and enteroviral infections
• Birth weight greater than 4,500 grams.
• Preeclampsia.¹
• Maternal age greater than 25 years.¹
• ABO incompatibility-induced jaundice.¹

Risk factors for type 2 diabetes include:

• Family history of type 2 diabetes in first- or second-degree relatives.
• Older age.¹
• Abdominal obesity.²
• History of gestational diabetes.
• The presence of hypertension and dyslipidemia.
• Ethnic background: African Americans, Latinos, American Indian/Alaska Natives, and Asians and Pacific Islanders have a greater prevalence.

Risk factors for GDM are listed below. In addition, individuals of Asian, African, Native American, and Hispanic ancestry have greater prevalence of GDM than non-Hispanic whites.³ The risk factors for GDM overlap with type 2 diabetes.

• Family history of type 2 diabetes in a first-degree relative.
• A previous abnormal oral glucose tolerance test.
• Glucocorticoid use during pregnancy.
• Polycystic ovarian syndrome.
• Age greater than 25 years.
• A prepregnancy weight at least 10% above ideal body weight.
• Early postpubescent weight gain.
• Previous child with birth weight greater than 9 pounds.
• Previous idiopathic perinatal death or birth defect
• Maternal birth weight greater than 9 pounds or less than 6 pounds.⁴