Diabetes is almost always a chronic condition of high blood glucose levels.^1,2 It is due to low or no levels of insulin, insulin resistance, or both.

There are 4 main types of diabetes:²

• Type 1
• Type 2
• Gestational – diabetes that develops during pregnancy
• Specific types due to other causes

Without treatment, people with diabetes have a much higher risk of diabetes-related complications such as:^1,3,4

• Hyperglycemic and hypoglycemic crises requiring emergency help or hospital treatment
• Cardiovascular disease (heart attack, stroke, ischemic heart disease)
• Kidney disease and failure
• Vision loss and blindness
• Neurological disease
• Sexual dysfunction
• Dental problems
• Foot ulcers and amputations

It is estimated that 34.2 million adult Americans (6.7 out of every 1000 people) have diabetes of which 90% to 95% of diagnosed cases are T2DM.³ Out of that 34 million, it is estimated that about 7.3 million adults are undiagnosed and likely have T2DM. About 1.4 million out of the 34 million have type 1 diabetes. About 1.5 million adults are newly diagnosed with diabetes every year with the majority being 45 years or older.

Type 1 diabetes is usually due to the autoimmune destruction of insulin-producing cells in the pancreas which causes complete insulin deficiency.^2,4,5 Markers of β-cell immune destruction include autoantibodies to insulin, GAD, and tyrosine phosphatases IA-2 and IA 2β and islet cell autoantibodies.⁵ Some people have idiopathic type 1 diabetes where no cause is found. Almost all people with type 1 diabetes are insulin-dependent.^2,4

Type 2 diabetes mellitus (T2DM) is a chronic disease of high blood glucose due to insulin resistance leading to insufficient insulin production.^2,6-8

Gestational diabetes develops during the second or third trimester of pregnancy in women who did not have diabetes prior to pregnancy. It usually goes away after giving birth, but it raises the woman’s risk of developing type 2 diabetes in the future. ^2,4 About 7.6% of pregnant women in the US develop gestational diabetes Diabetes is subsequently diagnosed in 19.7% of these women.

Other types of diabetes that are less common and have specific causes include:^5,10

• Damage to the pancreas from injury or diseases such as cystic fibrosis and pancreatitis
• Drug or chemicals such as HIV treatment drugs, glucocorticoid use
• Genetic defects of insulin-producing cells such as neonatal diabetes and maturity-onset diabetes of the young
• Hormonal diseases such as Cushing’s syndrome, acromegaly, and pheochromocytoma
• Organ transplant

^References

1. Vijan S. Type 2 diabetes. Ann Intern Med 2019; 171 (9): Itc65-itc80.
2. 2. Classification and diagnosis of diabetes: standards of medical care in diabetes—2021. Diabetes Care 2021; 44 (Supplement 1): S15-S33.
3. Centers for Disease Control and Prevention. National Diabetes Statistics Report. Atlanta, GA: Centers for Disease Control and Prevention, U.S. Dept of Health and Human Services; 2020.
4. National Institute of Diabetes and Digestive and Kidney Diseases. What is diabetes? 2016; https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes. Accessed January 16, 2020.
5. Diagnosis and classification of diabetes mellitus. Diabetes Care 2014; 37 Suppl 1: S81-90.
6. Beck-Nielsen H, Groop LC. Metabolic and genetic characterization of prediabetic states. Sequence of events leading to non-insulin-dependent diabetes mellitus. J Clin Invest 1994; 94 (5): 1714-1721.
7. Kahn CR. Banting Lecture. Insulin action, diabetogenes, and the cause of type II diabetes. Diabetes 1994; 43 (8): 1066-1084.
8. Robertson RP. Antagonist: diabetes and insulin resistance--philosophy, science, and the multiplier hypothesis. J Lab Clin Med 1995; 125 (5): 560-564; discussion 565.
9. Casagrande SS, Linder B, Cowie CC. Prevalence of gestational diabetes and subsequent Type 2 diabetes among U.S. women. Diabetes Res Clin Pract 2018; 141: 200-208.
10. Classification and diagnosis of diabetes: standards of medical care in diabetes-2020. Diabetes Care 2020; 43 (Suppl 1): S14-s31.