The Short But Sweet Summary
- The United States Centers for Disease Control and Prevention (CDC) says that 56% of new onset, correctly diagnosed Type 1 diabetes is seen in adults (age >20 years), and the CDC says that figure does not include the unknown number of cases of slowly progressive Type 1 diabetes that are misdiagnosed as Type 2 diabetes.
- In numerous studies, with the first study published in The Lancet in 1977, based on autoantibody testing, about 10% of people diagnosed with “Type 2” diabetes are autoantibody positive, have been misdiagnosed, and in fact have Type 1 diabetes. That 10% represents the largest group of Type 1 autoimmune diabetes. Michael J. Haller MD, in Type 1 Diabetes Sourcebook (ADA/JDRF, 2013), says “Importantly, adults with [slowly progressive Type 1 diabetes] may represent an additional 10% of those adults incorrectly diagnosed with Type 2 diabetes.”
- A recent Medscape article that used genetic data found that half of all Type 1 diabetes develops after 30 years of age (note that the researchers did not include subjects over the age of 60, so more than half of Type 1 diabetes develops after age 30).
- NovoNordisk, in their pamphlet "What You Need to Know as an Adult Diagnosed with Type 1 Diabetes" (reviewed by The Endocrine Society), states that 95,000+ adult cases of Type 1 diabetes are diagnosed each year. The SEARCH for Diabetes in Youth found that ~15,000 children are diagnosed with Type 1 diabetes each year.
The Longer Tale
New-onset Type 1 diabetes in adulthood is far more prevalent than childhood-onset Type 1 diabetes, but the myth that Type 1 diabetes is a childhood disease combined with the rising epidemic of Type 2 diabetes often means that adults with new-onset Type 1 diabetes are incorrectly diagnosed as having Type 2 diabetes, an altogether different disease. The myth that Type 1 diabetes is a childhood disease is a dangerous myth; for adults, the misconception can lead to misdiagnosis and the potential for rapid onset of diabetic complications and, in the most extreme cases, death due to diabetic ketoacidosis (DKA).
- In about 100 C.E., Aretaeus of Cappadocia provided the first detailed description of diabetes. Aretaeus of Cappadocia clearly described what is now called Type 1 diabetes (polyuria, polydipsia, rapid weight loss and swift death), and his descriptions were of adults. In Principles of Diabetes Mellitus, 2nd Edition (Leonid Poretsky, MD, Editor), the authors in Chapter 1 write: “A medical condition producing excessive thirst, continuous urination, and severe weight loss has interested medical authors for over three millennia. Unfortunately, until the early part of the twentieth century the prognosis for a patient with this condition was no better than it was over 3000 years ago. Since the ancient physicians described almost exclusively cases of what is today known as Type 1 diabetes mellitus [emphasis mine], the outcome was invariably fatal.”
- In 1934, Dr. Elliott Joslin noted that the incidence of diabetes in lean individuals was relatively constant in each decade of life, but that diabetes in the obese was related to older age.
- A book published in 1958 (“How to Live with Diabetes” by Henry Dolger, M.D. and Bernard Seeman) states that “[Type 1] diabetes is almost three times more frequent among young adults than among youngsters.”
And as stated in the short but sweet summary above, the CDC documents that the majority of new onset Type 1 diabetes develops in adults; numerous studies since the first published in 1977 provide evidence that ~10% of cases of “Type 2” diabetes are in fact Type 1 diabetes, based on autoantibody testing (GAD, IA-2, IAA, and ZnT8); and researchers using genetic data have shown that the majority of new-onset Type 1 diabetes occurs in adults.
Well-known people who were diagnosed with Type 1 diabetes as adults include actress Mary Tyler Moore (diagnosed at age 33), former acting Surgeon General Dr. Kenneth Moritsugu (age 49), Olympic swimmer (10 Olympic medals) Gary Hall, Jr. (age 24), and United Kingdom Prime Minister Theresa May (56). UK Prime Minister Theresa May is the first world leader with Type 1 diabetes; she was diagnosed with diabetes when she was 56 years old, however, she was initially misdiagnosed as having Type 2 diabetes.
My personal mission is raise awareness of adult-onset Type 1 diabetes, both rapid onset (which I experienced) and slowly progressive, to make sure no one else is ever misdiagnosed because of a myth. Type 1 diabetes is diagnosed at all ages, it is not a childhood disease, and it is important that patients receive a correct diagnosis and treatment. The correct treatment for Type 1 diabetes, at whatever age it is diagnosed, is exogenous insulin as early as possible, to control glucose levels, prevent further destruction of residual beta cells, reduce the possibility of diabetic complications, and prevent death from DKA. Medical doctors already know how to effectively treat Type 1 diabetes in children and teenagers; that excellence in care should also be applied to adults with new-onset Type 1 diabetes. When a child is diagnosed with Type 1 diabetes, the medical community springs to action on the child’s behalf, because Type 1 diabetes is a serious, life-threatening disease. Kids who are diagnosed with Type 1 diabetes are shown great compassion, and the disease is acknowledged to be profoundly life-altering. Yet often it appears that adults are not shown the same respect. For patients with adult-onset Type 1 diabetes, the person should be correctly diagnosed, treated with exogenous insulin, acknowledged as having a life-threatening disease, and treated with compassion.
 The U.S. Centers for Disease Control and Prevention’s (CDC’s) most current information on the prevalence and incidence of Type 1 diabetes comes from Diabetes in America, Chapter 3, “Prevalence and Incidence of Insulin-Dependent Diabetes” (Diabetes in America, Second Edition, 1995). Although people who use that reference as a source of incidence statistics state that there are about 30,000 new cases of Type 1 diabetes each year and that half of those cases are children; in fact, that source states that children (<20 years of age) account for 13,171 cases and adults (>20 years of age) account for 16,542 cases, for a total of 29,713 new cases of Type 1 diabetes per year, 56% seen in adults. Furthermore, that source states that there is an unknown number of adults identified as having Type 2 diabetes who have slowly progressive Type 1 diabetes.
 Irvine WJ, McCallum CJ, Gray RS, Duncan LJP (1977) Clinical and pathogenic significance of pancreatic islet cell antibodies in diabetics treated with oral hypoglycaemic agents. Lancet 1: 1025–1027.
 Miriam E Tucker, “Half of All Type 1 Diabetes Develops after 30 Years of Age.” Medscape, September 20, 2016.
 Type 1 diabetes in adults can be acute-onset or slowly progressive. Slowly progressive Type 1 diabetes is sometimes called latent autoimmune diabetes in adults (LADA). More recently, diabetes researchers have discouraged the use of the term latent autoimmune diabetes in adults, because LADA is not a latent disease. All people with immune-mediated destruction of the beta cells of the pancreas have autoimmune diabetes, classified by the Expert Committee on the Diagnosis and Treatment of Diabetes Mellitus as Type 1 diabetes.